virago running on one cylinder

[aaronchad]

 I have been trying to fix my bike for weeks now.. I cleaned the carbs and now my front cylinder in not running... Back one runs strong.. I can take spark plug off the back one and focuss on front one only and can get it to start but have to give it mid throttle just for it to stay running. I have tryed to set the idle control thing up under the bowls of the carb but it is not responding.. I can close it all the way or I can open it 6 turns and no change... still runs the same... Any ideas anyone?? 84 virago 700

new battery
carbs just cleaned
new plugs ( I am getting spark)
Fresh gas ( Iput some seafoam in it too)

[Geoffrey Gogan]

Hi.
I've found a few helpful members on this forum       http://viragotech.com/

I have an 81 750.  Had similar problems, and there are many others who have experienced this issue with the front cylinder.  One of the best reads had to do with vapor lock.  I personally have experienced this after a ride, when I park on the side stand, which leans the bike to the left.  There is a breather tube from each carb which I understand runs under the tank and through the frame.  It can become clogged causing something called "Vapor  Lock"   One guy said he uses a bicycle cable to run through the tube making sure it is clean of any little bugs or whatever.  This seems to have helped a lot of riders.   I'm going to try it.

I've always wondered if the tilt of the bike had something to do with the front cylinder problem.  
I'm pretty sure it has also happened more after a rain when the bike was left out.  I wondered if water was  finding  a low spot such as the plug hole, or possibly the wire connection to the coil.  It seems one of the two coils tends to rust much more than the other.    Certain weather conditions could be encouraging condensation too either clogging the tube at a low spot, or some other location where it can gather.  

I'm also looking at all the electrical connections such as up inside at each end of the plug wires as there can be corrosion that cuts down the amperage or voltage reaching the plugs.   The Virago has a weak spark to begin with.  One guy explained that as the starter is running it's even weaker.  The right plugs are really important on these bikes.  It seems the non-resisting type are needed.

I pulled my carbs off, but haven't reinstalled them.  I dipped them - soaked, thinking that might be the problem.   While I was at it, I ordered new bladders for the petcocks on ebay and installed them.  

Another weak spot with these bikes seems to be the vacuum system.  They are prone to leaks.  Leaks can happen anywhere along the system from the petcock, which requires vacuum, along all the hoses and connections.  Also at the carb inlet, where I noticed my O ring was broken when I took it off.  I still believe the left side - front cylinder side tends to be more prone to these types of issues related to condensation or moisture finding  a low spot.  

Another guy mentioned that some of the gas additives such as ethanol are deteriorating the rubber orings or fuel valve seats not allowing it to close properly.  My parts supplier said he got a spike of orders and thought it might be the fuel.   Those are the valves that close when the float rises .  if it doesn't close, fuel keeps flowing and will overflow.  You will see a little leak.
Many forum writers talk of how important it is to set the float level properly.  I don't know how they would get out of place, but there is a little sheetmetal tab that has to be bent so it touches the valve properly when it rises and pushes it closed.  I suppose it can, over time be bent by a sticky valve, or just from wear and tear.  repetitive movements pushing against it.    But the more common problem seems to be the opposite of a float that isn't high enough.  You can put a clear plastic tube over the drain, let fuel in, and turn the tube up to see where the gas level is in the carb.  They have to be level.  The correct level is 1 mm above the bottom edge of the top section of the carb where the bowl attaches to it.  The only way to get it right is to use trial and error, which requires removing the bowl.  Many make special short screw drivers, or replace the screws with allen screws and use a short allen wrench to make removal easier.  I plan to do this on the bench before reinstalling the carbs.  
Good luck.  I'll check back to see how its going.  I'm not a mechanic, so I'm just learning too.
[e-mail]  

[Chrysteria]

I have the exact problem with my virago, it will only run on one cylinder usually the back one.  I have tried to turn up the throttle under the carb and no response either.  

[bstig60]

If you are getting spark, does it miss at higher RPM also or just at idle? What does the plug look like that isn't firing after you run it for a while? Is it black and sooty or wet? If it fires above about 3000 RPM but misses below that or at idle, the most likely candidate is the TCI unit. There are two other possibilities, one is the float settings, the other is the pilot screw settings. Try checking the pilot screws first. Leave the rear carb alone, but turn the pilot screw in on the front carb until you get  a "soft seat". That means that you are starting to feel resistance. Don't screw it in hard or you might damage the seat and needle. Turn it back out (counter clockwise) to 2 1/2 turns and start the bike and see if you still have the miss at idle. You can adjust it one way or the other to get the best idle. Let us know................

[Chrysteria]

Just found out that I am for whatever reason not getting fuel to the front cylinder.  Runs on one cylinder throughout the whole rpm range.  Carb must be gummed up or something stuck in it, had this problem ever since I got the bike but it usually would eventually start to run on both pistons but not now.  I pulled the plug wire off of the one that it was running on and just put a spark plug in it and left the one in the cylinder to.  Then I pulled the plug from the front cylinder and poured about an ounce of fuel in the spark plug hole into the cylinder and put the plug back in and tried to start it to see if it would run on the front cylinder, and yes indeed it ran till the fuel got burnt up and then it died.  So the front cylinder is not getting fuel, the front spark plug looked kinda wet but obviously it was not getting any fuel.  The plugs are good and both have good spark, I could switch the plugs from one to another and it always would just run on the one cylinder.  Had the carbs cleaned at a shop about 4 or 5 yrs ago cause I was having the same problem, and now its back again, so something is sticking in there.  

[bstig60]

Very likely that both the pilot jet and the main jet are plugged. Below is a procedure for cleaning Hitachi carbs. It is for XJ's but applies equally well to XV's carbs. Check it out.


Remove the four Cross-head (Or Phillips) screws holding the Fuel Bowl to the Carb Body.
Set the four screws for Number - 1 in the bottom of your lined-up Muffin tin.
Go ahead, take-off the Float Bowl.

Spray some cleaner in the Float Bowl letting it accumulate half-way ... set the bowl down -- level --and let the Carb Cleaner work on the Fuel Bowl's metering ports at the bottom.

There's the business-end of your Carb exposed. The float is hinged. In the middle of the hinged part you'll see the "Float Needle Attaching Tab." There will be a tiny wire across the tab. That's a spring that is attached to the Float Needle Valve. Hold the Carbs up and get a close look at how the Needle Valve attaches to that tab.

Between the two float sections are the two numbered Jets, and hidden from view by the large Main Jet is a long, multi-ported, internal emulsion tube.
***(Emulsion tube will be referred to as NOZZLE in this article.) ***
 
Below the Float Needle Tab is the Float Needle and the Float Valve Assembly.

Slide the hinge pin out; drop it in the Float Bowl and let it soak in cleaner.
Carefully lift off the Float ... bringing the Float Needle straight up and out.
Take the Float Needle and the Float itself and place them in the next empty bin.

Being mindful that it is BRASS ... use the appropriate socket or boxed-end wrench and remove the Float Valve Assembly. Slight impact on the wrench will loosen the Valve Body allowing it to be turned out.

Do NOT allow a Float Hinge Pillar to become damaged during cleaning processes.
Depending on Year and Model the Float Valve may be:
1) Threaded.
2) O-ringed and just pushed-in … or,
3) Attached by a little forked holder bracket and a screw.

Upon removing the Float Valve; examine the end that was inside the Carb. On most Factory Valves, there is a little, tiny, "Beanie-looking" filter screen. The filter screen does snap off for removal. Only take it off if it's rusted-out or you plan to lose it!
Otherwise ... just shoot cleaner through the body to blow out the whole thing. Keep a close eye on the filter screen when you shoot the cleaner through it!

Put this Valve Body in the bin with the Float and Needle ... store these parts together and don't let them get mixed-up with other Float parts as you clean the other Carbs.

On the high post is the Main Jet.

Wipe off the bottom of the large Main Jet. Read the engraved numbers on the bottom of the Main Jet and write down what that number is in your Note Book.
There is a copper washer that the Main Jet holds in place.
Remove the copper washer and store it with the Main Jet, in the next bin up. If the storage bins on the muffin tin are fluid tight; spray Carb cleaner in it and let the Jets soak in Carb cleaner.

The Lower Post:
Smaller Jet than Main Jet.
Wipe-off and record the number.
Pull this Jet and let it soak, over in the same bin, with his buddies!

Near the frame rail -- you'll see a very small diameter brass tube sticking-up from the Carb Body.
That's the Siphon Tube. This tube supplies fuel up to the Cold Start Enrichment Circuit. The tube has a very small fuel metering port at it’s open, bottom end.
That tube extends into the special well designed for it in the wall of the Float Bowl.

The Siphon Tube, having such a small metering port, and extended into the Float Bowl well -- supplies fuel to the top end. It's size and the relatively small volume of fuel within its supply well allows fuel to be drawn-up the Siphon Tube with the relatively low vacuum drawn on it when starting-up the engine.

Probe the opening on the tube and insure that the metering ports supplying fuel to the special well the tube extends into, on the Float Bowl, are clean and allow fuel to fill the Fuel Bowl’s well. The fuel drawn-up through this narrow tube from the small well is the needed supply for cold starting. This is the Cold Start Enrichment Circuit’s vital fuel supply.

Well ... you cracked the Bottom-end and removed those parts ... Not bad. Everything needs to be cleaned, now. If you’re lucky ... there isn’t much to do. On the other hand, if it looks like a Highway Crew passed through that Fuel Bowl and Bottom-end and did a nice job with putting-down tar or varnish ... its all got to go! Clean everything until all surfaces are 100% Clean and look Brand New.
++++++++++++

"Overhauling Everything Topside"

Before we even touch a screw to begin the work on the top-side; let’s get the notebook and make a sketch. Believe me ... you WANT this sketch.
(Or do a non-Old School trick and take a nice close-up picture of the 4-Hats, clips and hold-downs -- AND -- Especially, how all the linkage to the four ENRICHMENT VALVES is oriented.

(Tech Note: Enrichment Linkage -- Right to Left -- as viewed from the TOP of the Carbs with the Enrichment Circuit linkages UP -- Carbs oriented 1,2,3,4 as you look at them on the bench.)

The 4 Enrichment Circuit Pivot Arms TOP.
ROD extending through the four PIVOTS with 4 - FORKED, Valve-opening "fingers" BELOW the ROD ... and attached to the ROD with SET SCREWS, which fit into DETENTS drilled to keep the SET SCREWS from slipping.

Orientation of Parts:

Right - to - Left

#-4 Fork with set screw <> Small Nylon Bushing <> Pivot Arm <> Large Nylon Bushing <> Cable Pull Bracket <> #-3 Fork with set screw <> Pivot Arm <> #-2 Fork with set screw <> Pivot Arm <> #-1 Fork with set screw <> Pivot Arm.

This mechanism is what is inaccurately called "CHOKE" by YAMAHA. But, since convention dictated that "Choking" was necessary to start a cold engine ... and, because CHOKE was easier for everybody to understand ... it’s called the CHOKE.

You can now call it what it really is: The COLD-START ENRICHMENT VALVE CIRCUIT.

Mark for Identification:

Center Punch a dot at the RIGHT end of the ROD ... right in the middle of the flat spot at the very end. The center-punched "Dot" ... is to identify the RIGHT side of the ROD. The 20-seconds it takes to Punch the dot on the end will save you a lot of time trying to figure-out which end is what ... when we put everything back together. This is Old School Technique ... tape and marks from marking pens will be long-gone after the ROD is cleaned and overhauled. Your center-punched dot will be right there ... no mistakes ... next time; too!

Remove the 4 - SET SCREWS attaching the FORKS to the ROD.
Note the way that the CABLE PULL ARM attaches to the ROD. ("Reversed letter J")
Draw or photograph how this is attached for accurate reference.
Remove the SCREW attaching the CABLE PULL ARM to the ROD.

Slide ROD to the LEFT.
Collect and save, in order, all the parts, which are attached to the rod.

(Editors note: Those setscrews can be replaced with aftermarket standard hardware. I prefer small ALLEN CAP SCREWS -- most well-stocked hardware stores have them.
Pimped: Black. Bling-bling: Stainless)

Next time: The Enrichment Valves come OUT!

"Your life is about to be enriched"

REMOVING THE ENRICHMENT VALVES and DIAPRAGM ASSEMBLIES.

With the linkage for the Enrichment Valves removed. The four Enrichment Valves are exposed, along with access to the Pilot Screws ... just to the left of the Enrichment Valves.

There will a Chapter devoted to the Pilot Screws, later. Right now, lets get on to the Enrichment Valves and continue the Carb Cleaning process.

The Enrichment Valve each have a rubber dust boot covering them.
Remove the rubber dust boots, which are best cleaned with dish detergent, rinsed -- dried, and soaked inside and out with Armoral.

After removing the dust boots ... Remove the Enrichment Valves in order.
These parts are Brass and may be very difficult to "Get started" out.
Hold some torque on the wrench and whack the wrench with a hammer handle to supply impact to get these fittings moving out.

The Brass housing comes out.
Sometimes the complete Valve assembly will come out.

Orientation:
The Enrichment Valve is a Brass cylinder with a tapered seat and a Pin-like protrusion on its business end.
The upper section has a spring around the shaft of the valve stem, which pushes closed the valve when the valve is closed by the relaxing of the cable controlling the linkage.
The stem has a "T" shaped top that is channeled to allow the forks to open and close the valve.
The valve should move very smoothly within its cylinder.
The Top Hat -- "T" -- should be square at the top of the shaft and not deformed or bent. If it is deformed or bent ... great care must be exercised to straighten it. Roll the shaft on a flat surface and lightly tap in the "High side" to get the Top Hat squared-up atop the shaft.

With the Enrichment Valves removed we move on to the Carb Top Covers.
The Carb Top Covers are often called: Hats. They can be shining chrome ... or, ugly looking, pitted old chrome. The ugly ones can be refinished and painted to look nice, again.

Remove the four screws attaching the Hat to the Carb Body.
If the screws are frozen ... DO NOT try to muscle them out. The top of the screw will break-off and you'll need to do drilling and tapping to get the chunk out and cut new threads for a new fastener.
Use a Hand impact tool if this is the case. Use Vice Grips on screws with ruined slots.

When the four screws are withdrawn ... the Hat comes free and a long spring like a "Slinky" toy pops out like "Jack in the box."

The spring is the Diaphragm Assembly return spring.
Remove the spring and place it in your organizer tray.
Exposed is the Diaphragm Assembly.

Lift-out the edge of the rubber diaphragm from around the circumference of the Carb body ... noting that there is a locating channel for the edge of the rubber diaphragm machined in the top of the body ... AND a locating TAB for the diaphragm to be correctly placed back in the cylinder upon reassembly.

Carefully extract the diaphragm assembly taking GREAT CARE -- NOT -- to bend or otherwise damage the long, NEEDLE VALVE at the bottom of the cylinder.

With the diaphragm assembly's removed and safely stored ... the Brass NOZZLE -- into which the MAIN JET was attached at the bottom can be removed by inverting the rack and gently tapping the Nozzle -- UP -- through the TOP of the Carb body.

Nozzles:
Solid brass cylinders. Multiple tiny AIR metering ports. Some NOZZLES are "Slotted and Keyed" ... Others are simply "Press fitted" ... some are loose enough to fall out the top without even touching them.

The NOZZLE is the POWER VALVE. Notice that there are 16 - 24 tiny metering ports drilled along the sides ... directly opposite from the ones on the other side. Hold the NOZZLE up to light. You must be able to see light through the ports near you coming through the ports on the opposite side. These very tiny metering ports can be clogged with dried-out gas that forms a hard varnish-like substance.
SOAK the NOZZLES for 30-minutes, completely submerged in Carb cleaner before beginning to clean them with the correct fitting tool from the Welding Tip Cleaner set.

Coming up next:

Pilot Screw Removal ... Do's, Don'ts and "Don't even think about its!"

PILOT SCREW REMOVAL / CLEANING

Preface:

There are three scenarios.
1) Factory Anti-tamper Plugs still in place
2) No Plugs. Screw slots visible and good.
3) No Plugs. Screw slots visible and looking pretty shaky.

As to #-1 above. There are pro's I know who will not disturb the plugs. They say: "They we're put there for a good reason. They get set right at the Factory and never need adjustment again." This is bullshit. All they want is the money from the next job without tweaking the one they should have.

If you still have the infamous "Anti-tamper Plugs" in place ... remove them! Your bike cannot be fine-tuned with those plugs preventing you from making a precision mixture adjustment of the Pilot Screw.

How do you remove them?

I chuck a very small Number Drill into my Dremel Tool and go at that plug like a Dentist. The plug is about the width of a Dime or less! I touch the drill bit to the center of the plug very, very lightly. Once the tip of the drill penetrates through that thin plug ... you need to be able to STOP further penetration. The danger is doing harm to the Pilot Screw top beneath the plug.

The slot of the soft, solid brass, Pilot Screw is right beneath that plug. Don't mess it up by touching the slotted top with the drill bit. Soft brass gets chewed-up by the drill bit really quickly. Faster than you can say, "Oops!"

To get the plugs out; screw a sheet metal screw, or a dry wall screw into the hole and continue your Practice of Dentistry and extract it by pulling on the inserted screw with pliers, vice grips or a small "Slugging Handle." Wiggle and pull. The plug comes out and the Screw is visible.


When you get the four plugs out ... oil the four holes with WD-40, or some other very light machine oil.
-------------------------
SCREW TOP IS VISIBLE AND LOOKS GOOD.
Don't start throwing the confetti around just yet.

SCREW TOP'S VISIBLE AND LOOKS PRETTY HACKED-UP
Sound "General Quarter's" and get ready to do battle.
[align=center][color=red][color=red][b]<><><><><><><><><><><><><><><><><><><><><><><><>
The absolute, Number One Rule, for performing work on Pilot Screws is: "Use the right tool."
If you have to run-out and buy a brand-new screwdriver, bring it home, and step right over to the grinder, to fabricate the necessary tool needed for Pilot Screw work ... so be it!

You NEED a screwdriver that fits the slot at the top of that Pilot Screw with absolute precision. Make one. Grind, file, sand, shape ... do whatever you need to do to make the blade of the screwdriver fit the slot on the Pilot Screw with ZERO free-play. None.

The wings on the top of the slotted screw are very soft brass. Unless the tool fits with such precision as to apply turning force to the entire mass of the screw, the WINGS will move without the main body of the screw moving along with them. An ill-fitting tool will allow the wings to move "toward un-occupied space" without the body of the screw moving with them. They will bend. Any attempt to unbend them will break them right off the top. Bad news!
<><><><><><><><><><><><><><><><><><><><><><><><>[/b][/color]
[/color][/align]Game time:

Bottom line!
One way or another, the Pilot Screws need to come out.
They may be:
a) Simply withdrawn.
b) Removed with some dexterity and effort.
c) Extricated; using all available resources ... maybe even the "Jaws of Life."

If you are one of the lucky ones who had these screws protected by plugs; this might go as smooth as silk.

Dab-out the puddle of WD-40 with a Q-Tip leaving a trace in there to help the process. Using the proper tool ... and, with a Watchmaker's gentle touch ... turn the screw IN. Yes; IN. In and down until the Pilot Screw "Bottoms-Out." As you do so ... count the revolutions needed for the screw to be turned IN until it bottoms. (Generally, this will be approximately two and one half [2-1/2] turns. If the adjustment is more or less – write-down the measurement for using as your preliminary adjustment OUT when the screw is replaced after Carb Cleaning. Do the same for all four.




If you are less fortunate and find the plugs removed; but the Pilot Screw slots are in good condition. Clean out the area above the top of the screw. Get the space meticulously clean. Use a generous amount of Carb Cleaner, and the point of a jumbo safety pin, that has had its tip heated and bent-over to be used as a surgical instrument. The entire space above the top of the screw needs to be meticulously cleaned -- with special attention to carefully scraping clean, the ULTRA-fine-threads above the screw.

Once cleaned-out; flush out with Carb Cleaner ... re-oil and attempt to turn the screw IN and DOWN as stated above. Using great care, attempt to get the screw to move. If it does move, attempt to bottom-out the screw as previously mentioned.

(If it does NOT move ... it is possible that someone could have left the screw already bottomed-out and not adjusted properly. If you are cleaning the set because the bike sat un-used for some time, runs like crap, stalls a great deal, was hard to start or would not idle ... it is possible that the screw IS bottomed-out and is the source of all that difficulty. If you suspect this is the case by comparing the height of the screw top to the others ... then, attempt to bring the screw OUT.)

If that screw doesn't move either way under gentle pressure ... STOP!
Don't fool-around and "Chance-it." Get-out the Propane Torch ... time for heat!

Clean out the area of all the WD-40 with Carb Cleaner. When the Carb Cleaner evaporates apply several drops of -- >> OLIVE OIL << -- to the space above the screw top.
The Olive Oil is a vegetable product; not a petroleum based product. The Olive Oil will not ignite as readily as a petroleum based lubricant will; and will boil-away that which is not brass or aluminum while also acting as a penetrating lubricant.

Heat the surrounding aluminum area well. Sop-up the Olive Oil and make another attempt to move the screw. When it moves ... bring it UP into the oiled and heated area where it should begin to turn much easier allowing you to get it out of there. Forget about bottoming-it-out. At this point, you're better off -- "Getting them out."
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

"Rescue-One, Paramedic-One, respond to Hitachi Carbs ... reported severe head trauma ... Units respond Code-3"

Now, we deal with the tough issue of getting-out Pilot screws that somebody really did a number on. There's good news; and there's bad news. The good news is that the Pilot Screw is made of Brass. The bad news is that the Pilot Screw is made of Brass, too!

The damage is done. Before you arrived, somebody did a hack-job and "Screwed-Up" ... Big-Time. They messed things up good. You're mission is to UN-mess-up this situation.
Don't begin working on this project if you are angry or frustrated. You need to be in total control and able to systematically perform the various steps we'll need to take to get them out.

Job One is: "Get them OUT!" Period. We do what it takes to get them out and deal with all the other stuff -- later.



Phase One:
Take a shot. Your turn. Evaluate. If it looks like there might be enough of a slot left to back that thing out of there, or you might be able to do some Dremel Tool surgery to improve the situation -- have at it! Then, Olive Oil and heat it up good. If this gets things moving; back it out. Muscle it if you have too. The damage was done before you arrived. You might get lucky and the damn thing will give-in and come out.

Phase Two:
First "Drilling" procedure. Using a seven sixty-fourths
[7/64th's] inch drill bit ... chucked into your Dremel Tool ... drill a small hole ... dead-center of the screw ... just deep enough to get a Number-2 Screw Extractor ... better known as an "Easy-Out" in the drilled hole ... and make your first attempt to bring the Pilot Screw out of there. Tap-in the Easy-Out to get the tool a good bite before you start backing it out.
Yes? Celebrate a small victory!
No?

Phase Three:
Just like Phase Two. Bump-up one size. Five thirty-seconds drill bit. [5/32nds] Number-3 Easy-Out. You should be victorious. When oiled, heated and coaxed-out of there with the Phase Three approach ... there is still the possibility that the Pilot Screw can be brought back from the dead.

Phase Four:
Drill the Pilot Screw with progressively larger bits until there is just enough brass remaining to protect the Ultra-fine threading on the Carb body from being damaged. Then, using a Dremel cutting tip score though the brass, length-wise, at 12 O’clock and 3 O’clock and "Pick-out" the piece you scored for removal. Followed by Picking-out the larger section, too.

Keep your eye on the prize.
Job One!

If you don't have a Dremel Tool, the right sized drill bits and the Screw Extractor Set; you will, after you make sure your Credit Card is in your wallet and arrive back home, from Sears!


The Home Stretch:
> Pilot Screws and Enrichment Valve Components and Removal
> Clean-Tuning and re-assembly prep.

As we round the far-turn and approach the Finish Line for Cleaning Our Own Carbs; these final few procedures are where you “Earn your Stripes” and do what is necessary to gain the very Maximum of Performance from the bike when we've done all the cleaning and “Clean-Tuning” steps necessary to allow the bike to run – “Perfectly!”

We need to extract all four of the Pilot Jet Mixture Screws and their internal components. We also need to extract all four of the Enrichment Valve Assembly’s and springs.

Then, with all the Jets and Internal parts removed; clean and blow out the fuel and air passages before re-assembling the rack and tuning the Carbs to the very edge of their fine-tuning capability.


> Removing the Pilot Mixture Screws and Component Parts:

Because the Pilot Screw has such a very fine thread pitch they can be difficult (If not impossible) to move. Cleanliness is the key to their removal. The cleaner the area above their screw slots is; the easier they can be loosened and removed.

As mentioned, many times before, use (or make) a tool that fits the slot with Watchmaker’s Precision. Keep the threads lubed-up with light machine oil. These are precision components. Handle with care.
The hidden spring, washer and O-ring in the Pilot Screw housing are the tiniest parts on the bike. Take every precaution NOT to lose anything!

Take the appropriate measures to work CLEAN, on a surface prepared for working clean and free of any place a small (Really, very small -- we're talkin' >Teeny-TINY< part might fall into or disappear. Spreading some old bed sheet or linen beneath the work is a good idea.
- - - - - - - - - - - - - - - - - - - - - - - - - - - - -

Each Pilot Screw must be withdrawn complete with its associated parts within the small chamber beneath the threaded head and stem of the Pilot Screw. Prepare for handling 4 (four), SMALL, easily lost, precision parts:

1. The Pilot Screw and Stem with its pinpoint Precision Metering Tip. (One piece.)

2. Pilot Screw Tension Adjustment Holding Spring.
(May come-out surrounding the stem on the screw. Might need to be lifted-out if it remains in the Carb body when the screw is lifted-out.)*
Visually check bottom of spring for tiny flat washer.*

3. Very, very, very-small Flat Washer.
(Might be stuck to the lower end of the Spring or remain, in -- at the bottom of the housing needing to be extracted.)

4. A very tiny O-ring. About the size of this letter >: “o” .
The flat washer and O-ring are usually found at the bottom of the housing. They might be lifted-out when the spring is withdrawn; so check the end of the spring.

[My “Special Tool” for fishing-out the tiny Flat Washer and the O-ring from the bottom of the Pilot Screw housing is just a long “Safety-pin” that I heated and put a small angle on the tip.]


> The Enrichment Valve Removal. (See! They're NOT Chokes)

The Enrichment Valves come in a couple different flavors. There are Solid Brass Valves with a tapered seat end and a further narrow pointed shaft-pin seat; and there are some with a “Barrel-style Plunger” having a rubber seat attached to the base of it’s Barreled end, also-- shaft-pin ended.

Removal:

Remove the rubber dust cover. (Clean; let soak in Armoral)
Loosen and unscrew the Hex-topped brass body.
Remove the entire Valve, spring and brass body together. (Separate and clean individual components before re-assembly.)

Once the Pilot Screws and Enrichment Valves are removed from the Carb Bodies, there are but a few “Air Jets” remaining in the Intake Port and beneath a screwed-on cover plate, where the rubber diaphragm seats; some models have an “Air Jet Cover” which needs to be removed to INSPECT these Jets. Others have had the cover OMITTED at the Factory.
Many others have had the cover OMITTED during Carb cleaning and maintenance.

Note: There is a threaded opening for the special screw, which serves to attach the Air Jet cover, if so equipped. If you are going to withdraw all the Air Jets for Air Passage cleaning ... SCRIBE an "X" next to this threaded hole so it will not be confused as an Air Jet Passage.

The Air Jets are all slotted and threaded for easy removal. But, since the openings in the center of the air jets are large enough to permit the Carb cleaner spray tip to enter and shoot the air passages clean … you may (at your option) leave the Air Jets in place and spray and blow-out the passages without removing the Air Jets.

If you MUST remove all the Air Jets, for dipping or sonic cleaning the Carb bodies … ID each Jet for > PROPER REPLACEMENT < Particularly the two Air Jets in the TOP cavity beneath the Diaphragm Assembly!

Certain Workshop Manuals show these Air Jets replaced > Incorrectly < !!! Following the illustration and placement shown in the HAYNES Manual will lead to a situation which REVERSES these two Jets ... making adjusting the correct air mixtures impossible without actually having the right sized air jet in the right place. A tune-up troubleshooting nightmare!

If you are using a HAYNES Manual -- Do NOT extract the Air Jets from this area UNTIL you have:
MARKED the Jets and Carb Body for ACCURACY -> AND made the appropriate CORRECTIONS to any incorrect HAYNES TEXT and ILLUSTRATIONS before the confusion results.
“Clean-tuning” the rack.

"Clean-tuning" is the process of making the rack ready to accept all the cleaned component parts. There are a few very important “Clean-tuning” processes.

1. The Diaphragm Assembly “Clunk Test”.
Please read and review this “Clunk Test” and perform the necessary steps to prevent Diaphragm Assembly Sticking – or – “Stiction”. This test insures that you will be able to fine-tune your Carb's for MAXIMUM Performance!

With the Hat off ... spring out ... and diaphragm un-seated to its locating channel -- LIFT the brass piston to the top of its travel and let it fall. The Piston needs to FALL! It absolutely MUST drop ... from being raised-up and let-go ... like a safe out a second-story window! If it chatters down, hesitates, acts like it being hydraulically controlled, is slow, stops and goes ... or, does anything, other than DROP ... like a wet bag of cement ... you've got a performance problem. SLIDE PISTON STICTION. Get rid of it. It's easy enough to do.
Polish the brass piston. It should be a shining brass object a Marine Corp Recruit would be proud to show his Drill Instructor. You can polish the needle, too! BUT -- DON'T bend it!
The Carb Body Bore is usually where the problem is. A film of oxidation forms on the Inside Diameter of the cylinder bore surfaces. This film reduces the inside diameter's already close tolerance to make the brass piston's travel become impaired. Elbow grease and finishing papers will restore the original shine to the alloy.
Use # - 800 Wet-'O-Dry to clean the surface. Vertical motion only. Refinish the bore with 800 using WD-40 as the wetting agent. Using sections of 800 about the size of a pack of matches ripped in half ... refinish the inside diameter of the bore. Throw-away the 800 section as it becomes fouled. Refinish UP and DOWN ... moving ALL AROUND. Don't do anyplace where you think its sticking. Keep the bore round.
Feel like doing another 15-minutes of work that will give you a Full Stage closer to RACE-PREPPED??? OK ... after you clean-up the bore with the 800 Wet ... Hit all the bores, AGAIN, with 1000 - 1200 and 1500 !! WD-40 is your wetting agent. When you are done, there should ZERO drag. Nothing preventing the diaphragm from raising the piston when vacuum is present. And, NOTHING from preventing that SPRING and NO VACUUM from allowing those slides to slam-shut for some ABSOLUTELY wonderfully controlled engine braking when you've got your Carb's - "Dialed-in!"

2. The “Sync Screws” and linkage.
While you have the rack where you can access all the “Moving Parts” and make sure they move as they are supposed too. Loosen each Sync Screw and oil the threads on the screw and linkage. “Exercise” each of the THREE Sync Screws, IN and OUT, within their mount on the linkage, until you are satisfied that you have attained the ability to make precise adjustments to the Sync Screws without any binding or getting held-up by rust-dust or other oxidation.

=============================================

You have reached the Summit. You stand atop the peak you dared to assault. But, getting to the top is only half the story. Now, you reverse course and head back down to where this all began. It’s a joy to have cleaned your own Carbs. You have absolutely NO doubts about their cleanliness! So, don't hurry the process of putting them all back together.

”Assembly is in the reverse order of taking them down and cleaning them” … the Books and Manuals always say. If there were no major complications getting you along this far … the process of re-assembling your Carbs, hanging them back on the bike, firing-up the bike and doing the REAL fine-tuning is just a matter of time.

[rhausman]

I had the same problem this spring.  I called a Yamaha dealer and they wanted $70/hr to clean both carbs.  They said would be a 3-4 hour job.  I took the bike to my uncle (a retired mechanic and motorcycle rider).  He took my carbs apart and found that the needle was sticking in a 1 carb.  I purchased 2 of them (since he said the carbs were a "bitch" on this bike) so I would not have this problem on the other carb later.  I got the part (Needle valve set..part# 3CF141071500) on-line for $51 each.  The bike runs wonderfull again.

[ViolinARC]

Read my experience here and you may solve your problem...

http://www.nabble.com/Probable-Solution-to-the-%22Firing-on-One-Cylinder%22-Issue...50MPH-at-WOT-No-More!-to24692447.html 

[ViolinARC]

YIKES!!!! Very detailed write up but the reason I was dreading ripping my carbs apart and as you may have read, many have already reconditioned their carbs and are having the same experience. Try reading this first and you may solve your problem permanently: http://www.nabble.com/Probable-Solution-to-the-%22Firing-on-One-Cylinder%22-Issue...50MPH-at-WOT-No-More!-to24692447.html

[bstig60]

Wiring problems can certainly cause some of the problems you speak of. Broken or corroded wires and connectors are a problem on any older bike. Also, grounding is another problem with older bikes. Not to mention the various switches and relays. The best way to diagnois wiring problems is with a good wiring diagram and a voltmeter and some patience.
However, with the earlier Virago's that use the Hitachi carbs, many of the same problems are caused by poor carb adjustment, vacuum leaks and dirt or debris in the carbs. Hitachi's have to be squeaky clean and the pilot jet system is the biggest culprit since the passages are very small and difficult to clean properly. Backfiring through the carb or exhaust can be caused by running too lean or running too rich, so it is always a good move to check your carb adjustment first, particularily the pilot screw adjustment.

Thanks,
Bill

[ViolinARC]

My bike was exhibiting these symptoms (backfiring that is) from the very beginning (as stated, 3x's the "pros" kept telling me that it was "normal" operation for a V-twin) and 15-years later, I discover a short and repair it. Now, the backfiring has completely vanished so I can't say the short occurred due to age and I certainly don't agree that it's "normal" operation. However, I can say that it was probably worsened over time due to the movement of the steering head though cause the dropped cylinder (in combination with the backfire) didn't start occurring until last year.

afaik, the problem has been licked cause it's been several days and many miles without a single operational issue...if you're having this issue, check for the short first. What do you have to lose?!?

[skeezix]

There is another issue that happened to me today.  I have a 1981 XV750 and it was running on the rear cylinder only.  The front cylinder has 2 vacuum lines coming from the carb/manifold joint.  Make sure this joint isn't cracked also (spray some brake cleaner around it will running, see if it starts firing or idle jumps).  The vacuum lines from this joint run to both the right-side fuel cock as well as the air mixture control valve, which is located behind the front-left frame.  This valve can cause a lot of problems, and if the vacuum isn't present in this line then you won't get fuel to the front cylinder if the petcock is on the 'on' or 'reserve' position.

Get the bike started and running (if possible!) and change the right fuel cock to 'prime' - this will let fuel flow regardless of vacuum, and if it starts firing then either you have an issue with the fuel cock, or a vacuum (or air mixture valve) problem.

My problem today was that the carb was delivering fuel but wasn't getting anything from the petcock so it ran out for the front cylinder and I was running only on the rear. I checked this by taking a feel at the pipes and the exhaust from the front was cooling down, the other was hot hot hot.  I couldn't get the bike to stay running or start back up, so I changed the right-side petcock to prime and left it there, and after about 20 seconds I tried starting again.  A few tries later it started and both cylinders were firing.  I got back on the road, moved the right petcock to 'on' and after about 1/4 to 1/2 mile it started missing again on the front cylinder, and soon as I moved it to prime (while moving) it started firing fine again.  That tells me I have either vacuum leak, petcock issue, or air mixture valve which would also cause vacuum issues.

For vacuum lines (from memory) - the big nipple on the front manifold/carb joint goes to the air mixture valve.  The small one is split 3-way - 1 goes to the carb/manifold joint, another to the air mixture control valve, the 3rd goes to the backside of the fuel cock.  Any of these may be leaking, or the air mix valve may be having issues and can probably be removed provided you fix the vacuum lines to compensate.

Hope this helps!