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ViragoTechForum.com » Tech Help » Problem, XV 920 coughing and sneezing. (SOLVED)

#1: Problem, XV 920 coughing and sneezing. (SOLVED) Author: RagtagRider,

Posted: Mon Aug 30, 2010 3:46 pm

Hi all, I am new to the forum, and here is my first post, problems of course..! :)

I have a little problem with by bike. It has been standing for couple of years, after which I bought it and now I am trying to bring it back to life.

When I first drove it, it worked quite ok, but seemed to be somewhat lazy, so I opened carbs to see if there is some dirt etc. Both of the carb membranes had several holes, which I fixed using Gorilla Glue (which was probably bad idea, because it is way too hard after it dried). Anyhow, I put those "fixed" carbs back and went on a testride. To my surprise the bike is now functioning worse than before all that carb cleaning and membrane fixing!
With low rpm (under some 3000-3500 rpm) engine hesitates, coughs and sneezes, and on the traffic lights it might even die, after which it is reluctant to start again.
After test drive I took spark plugs out, and the result was: front cylinder plug was very very white, and rear cylinder plug was very very black.

So, what might be the problem? Maybe the membranes are broken again because of that too hard glue? Maybe I should synchronize carbs (but can the lack of synchronization have such dramatic effect)? Or can it be some sort of ignition problem, although I havent touched the ignition timing at all? I also didnt check the fuel level at the bowls.

I hope you could give some advice, although I prob try to sync the carbs anyway, and if that doesnt help, I take them out once again.

Another thing, is there some upper limit how high speeds Cycom will show? Earlier I wasnt able to get it over 85 mph, and now I tried few pulls but always 140 kmh was the maximum. Although my clutch is slipping (problems, problems!) it is hard to believe I always hit exactly the same top speed!

Last edited by RagtagRider on Tue Sep 07, 2010 3:08 pm; edited 1 time in total

#2: Re: Problem, XV 920 coughing and sneezing. Author: arnie,

Posted: Mon Aug 30, 2010 4:38 pm

Don't know about Cycom, but you probably need new diaphragms. Make sure the carb is really clean. There are some very small passages in thee that need to be clean. I used a guitar string to clean mine after soaking for 2 days in cleaner. It will do no good to sync carbs if they are not right. This is one area that you can't take shortcuts on a Virago!!

#3: Author: grazingazer,

Posted: Mon Aug 30, 2010 6:52 pm

how 'bout telling us what it's actually doing...that way we can help you...is it backfiring out the carburetor[s]? is it making strange noises out of the exhaust...do you feel puffing out of the head gasket[s]...you prolly need to re-examine those diaphragms

#4: Author: RagtagRider,

Posted: Tue Aug 31, 2010 1:51 am

grazingazer wrote (View Post): › how 'bout telling us what it's actually doing...that way we can help you...is it backfiring out the carburetor[s]? is it making strange noises out of the exhaust...do you feel puffing out of the head gasket[s]...you prolly need to re-examine those diaphragms

It is not backfiring out of the carbs, nor head gaskets, but it is more like making short "pffts" out of the exhaust. At the same time the engine hesitates / misfires. And this happens all the time when driving with low rpm. With high rpm (>3500) there seems to be no problem. Based on the spark plugs it seems that front cylinder is running very lean, and back cylinder very rich.

About diaphragms, is it possible to change only the diaphragm itself, or is it necessary to replace the whole diaphragm+slide package at once? Is there good places to buy diaphragms?

#5: Re: Problem, XV 920 coughing and sneezing. Author: RagtagRider,

Posted: Tue Aug 31, 2010 6:57 am

More info about the problem, when I pull the choke on partially, the problem disappears. Is this now clear indication that diaphragms are broken? Or could it be some mysterious air leak?

#6: Author: grazingazer,

Posted: Tue Aug 31, 2010 9:24 am

why not install a new spark plug and see if the problem goes away

#7: Author: club_c,

Posted: Tue Aug 31, 2010 11:35 am

RagtagRider wrote (View Post): ›
... when I pull the choke on partially, the problem disappears...

You are running lean prolly because of a vacuum leak, and prolly at the carb mount. The hissing sound is likely your vac leak making itself really known. Spray some carb cleaner around the front carb holder while the bike is idling, since that is the one that appears to be running lean judging by your plugs. The idle will increase if there is a vac leak because it's pulling in the carb cleaner and burning it.
Regarding the diaphrams, you could try to repair with SealAll, which is a gas resistant flexible sealant. Replacement diaphrams are available through this guy on ebay:
http://cgi.ebay.com/ebaymotors/DIAPHRAGM-CARB-YAMAHA-VIRAGO-XV700-XV750-XV920-XV1000-_W0QQcmdZViewItemQQhashZitem3f02be9a04QQitemZ270628985348QQptZMotorcyclesQ5fPartsQ5fAccessories

I have used these with good success. I emailed him pix of my repair and he used them on his auction. I have no affiliation, but know these work.

#8: Author: TheMightyQuinn,

Posted: Wed Sep 01, 2010 12:36 am

As for your. CYCOM, it will only read to 85mph. Something about these years of bikes (don't know the exact dates when it started or ended) that they weren't allowed speedometers to read over 85mph. May have been for cars as well, but I'm not sure. So even with a digital readout, it stops at 85.

#9: Re: Problem, XV 920 coughing and sneezing. Author: RagtagRider,

Posted: Wed Sep 01, 2010 3:53 am

Thank you for your replies!

Obviously I have to do some experiments before pulling carbs out again:
1) Play with start spray to see if there are some leaks.
2) Inspect visually whether the slides are actually moving (and at similar rate).
3) Check the synchronisation.

And then I have to see what is condition of the diaphragms now. Maybe I also manufacture manifold for a single carb setup, it should halve the problems...

That Cycom thing is also quite funny..! :)

#10: Author: club_c,

Posted: Wed Sep 01, 2010 10:38 am

RagtagRider wrote (View Post): ›
Maybe I also manufacture manifold for a single carb setup, it should halve the problems...

No, it will double your problems trying to tune for proper jetting. If you think you've got problems now with carb tuning, get ready for a lot more trying to set up a single carb...

#11: Author: RagtagRider,

Posted: Wed Sep 01, 2010 12:19 pm

club_c wrote (View Post): › No, it will double your problems trying to tune for proper jetting. If you think you've got problems now with carb tuning, get ready for a lot more trying to set up a single carb...

That might be true of course. Somehow I really hate these carbs, and all the hassle they produce.
Another option is to plug in fuel injection, with Megasquirt. Though, I dont know if the generator can produce enough current to drive the fuel pump.

And after fuel injection, it would be relatively straightforward step to install a turbo! But I have heard that maybe these things dont produce enough oil pressure / flow to lubricate the turbo..?!

#12: Author: Matthew,

Posted: Wed Sep 01, 2010 1:38 pm

you can find a turbo FI project if you look around.

81-83 carbs often need cleaned a dozen times as its easy to miss something, pilot jet mod is a must also for tuning if you ask me.

search

#13: Author: club_c,

Posted: Wed Sep 01, 2010 1:50 pm

turbodog is working on turbocharging a 920, search his profile

#14: Re: Problem, XV 920 coughing and sneezing. Author: RagtagRider,

Posted: Thu Sep 02, 2010 4:30 am

RagtagRider wrote (View Post): › Obviously I have to do some experiments before pulling carbs out again:
1) Play with start spray to see if there are some leaks.
2) Inspect visually whether the slides are actually moving (and at similar rate).
3) Check the synchronisation.

Followed my earlier plan, and results were:
1) Start spray had NO effect. So probably there is no air leak.
2) Slides were moving easily when revving, and "probably" at similar rate.
3) Synchronisation - did not do that. Yet.
4) Installation of new spark plugs. Maybe slightly better, but still far from working one. On the plugs I didnt believe because choke helps problem, so it seems more like carb problem.

Ok, after these experiments I pulled out the carbs. Diahpragms are ok, of course there is this hardened Gorilla Glue, but as far as I could see, there was no holes. I also could not find any obvious dirt this time anywhere, in the first time another pilot jet was completely clogged and I thought that was a problem along with broken diaphragms! Funny thing, though, is that before disassembling the carbs even for the first time bike was working far better.. :S

Anyhow I found one thing that could cause the problems! Another pilot jet screw was open something like 5-6 full rounds (360 degrees), and another one was almost completely closed. What do you guys think, can this cause the symptoms I have had?
And further, what is the proper setting for pilot jet screws, I remember something like 2 and 1/4 rounds, is that correct, and are those full rounds (360 degrees)?

My hypothesis is that maybe someone has tried to compensate clogged pilot jet (and broken diaphragms?) by adjusting those pilot jet screws, and when I cleaned the pilot jet, everything went wrong. Does this sound possible?

Carbs are still off the bike, but I have to try to get them back to see if they work.

#15: Re: Problem, XV 920 coughing and sneezing. Author: Wrench71,

Posted: Thu Sep 02, 2010 5:06 am

Do the pilot jet mod like Matthew said. You just run a #76 drill through the pilot jets.

Next, while the carbs are apart, clean everything again! You did dismantle them completely and clean everything the first time right.......

Anyway, put em back together and bench test the float levels. Doing this before installing the carbs makes float adjustments much easier. Just use a small fuel resistant bottle and some fuel hose, hook up the line, fill the bottle with fuel and hang it above the carbs.

Once the floats are set right put em back on the bike. Set your pilot screws out about 2 and half turns.

Fire the old girl up. Once she's warmed up, adjust the pilot screws until you get the highest idle rpm then adjust rich until each one gives a little rpm drop.

Next, sync the carbs at idle then at around 3500 rpm.

Last, enjoy the ride!

Good luck,

Sean

#16: Re: Problem, XV 920 coughing and sneezing. Author: RagtagRider,

Posted: Thu Sep 02, 2010 7:57 am

Thanks Wrench71!

Just to keep things clear to myself, my next action list:
1) Pilot jet mod (http://viragotechforum.com/viewtopic.php?t=2082&), when I find 0.5 mm drill.
2) Fuel level test (carbs out of the frame).
3) Carbs back in.
4) Pilot screw adjustment.
5) Syncing.
6) (Hopefully) The ride.... :)

Only bad thing is I get to do these fixes on Sun or Mon. But maybe even before that I can start to prepare flanges for the single carb setup at different place..!
Single carb, if for nothing else, just for the experience, and because I have several Mikuni VM 38's laying around from sleds..

#17: Re: Problem, XV 920 coughing and sneezing. Author: arnie,

Posted: Thu Sep 02, 2010 9:24 am

Once I got my carbs clean and bike running right I have had no problem now for 2 years. All the power that I can use. I don't see how a single carb could do any better?

#18: Author: club_c,

Posted: Thu Sep 02, 2010 10:31 am

RagtagRider wrote (View Post): ›
1) Pilot jet mod (http://viragotechforum.com/viewtopic.php?t=2082&), when I find 0.5 mm drill.

Hobby shops in North America, maybe in Finland too?

#19: Re: Problem, XV 920 coughing and sneezing. Author: RagtagRider,

Posted: Thu Sep 02, 2010 10:42 am

arnie wrote (View Post): › Once I got my carbs clean and bike running right I have had no problem now for 2 years. All the power that I can use. I don't see how a single carb could do any better?

Of course single is no better if there is no need to do any adjustments, and I would be happy to get the originals running right! But as I have open plans for fuel injection and turbo, those would be relatively easy to plug in with single carb manifold.
Maybe in case of new airfilter or exhaust pipe arrangement there is need to adjust carbs, and in that case single is easier than double.
One point is also that original carbs are getting old and it seems maybe their time is running out, so with the same or even less cost I can try single out.

But speaking of what is reasonable, owning a bike is that not in the first place, and I have them three now.. :S

By the way, on weekend I am trying to check out second hand Mitsubishi TD04-09 turbocharger, it should be quite suitable for this bike when aiming to somewhere around 100 hp.

Just wondering, why my signature is not showing?!

#20: Author: grazingazer,

Posted: Thu Sep 02, 2010 10:54 am

your signature didn't show because you hadn't clicked the attach signature box...i just did it for you

#21: Re: Problem, XV 920 coughing and sneezing. Author: RUGER1022,

Posted: Sun Sep 05, 2010 9:13 pm

I have a 1983 xv750mk with the same problem.... what I did was first gave it a complete tune-up including plugs (gaped at .032), wires, had the carbs cleaned,adjusted and synced, changed oil and filter. I even went as far as to run a whole cycle of lucas carb cleaner and fuel treatment through it to try to solve the problem with no success. The only thing I have not tried was fooling with the ignition timing. This is the only rational thing left to try to remedy this problem. Is there anyone that can lend me some knowledge on how to perform this adjustment and what the specs are....thanx

#22: Author: grazingazer,

Posted: Sun Sep 05, 2010 9:16 pm

there is no timing adjustment unless you slot the holes on the stator that the pickups are screwed into

#23: Re: Problem, XV 920 coughing and sneezing. Author: RUGER1022,

Posted: Sun Sep 05, 2010 9:28 pm

that kind of adjustment is a little over my head so I will just have to deal with it thanks for the reply

#24: Re: Problem, XV 920 coughing and sneezing. Author: RagtagRider,

Posted: Tue Sep 07, 2010 3:06 pm

Ok, finally the bike is up and running! So thank you guys for advice!

I think main problems were dirt in the beginning, wrong adjustment of pilot screws and fuel level. During last weekend I checked the fuel level and I think in front carb it was off (low) almost one centimeter.
Today I plugged in the carbs, and after test run it feeled quite ok, but sparkplugs told me that front cyl was running very lean, and rear cyl very rich. Some pilot screw adjustment from the preset two and half rounds made the trick and now afr is near the proper region, I think.

One thing to be noted, regarding floats! While playing with fuel levels I had very strange readings at one point, only to notice one of my floats was upside down! Easy to do mistake if thoughts are wondering somewhere elsewhere...

Now that engine is working somewhat ok, I found another problem, slipping clutch, but maybe I post new topic about it (because it may be due to wrong type of oil..)!

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