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very strange Virago 920 issues (solved)

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very strange Virago 920 issues (solved)

PostAuthor: Yamahas rock » Wed Feb 06, 2019 1:30 pm

Hi everybody, I recently put Jardine slashcut pipes with the baffles removed from my 1982 virago 920 and would like to know if anyone knows what size main and pilot would be needed since it obviously needs to be rejetted. however, when i start it if i leave it idling for a minute it suddenly puffs white thin smoke from the pipes and, without being given any throttle what so ever it goes from 1000 rpm to 3000 and if I turn off the choke it dies. It only has 18,920 miles on it and has 144 psi cold on both cylinders and has had the carbs rebuilt last month and is not overflowing with oil. So the engine is in good shape. and all the electronics check out. Just to be clear, it has NOT had the diagraphrams replaced ever. this bike only cost 150$ from a garage sale because sadly some sweet old lady's husband passed away and she was in a hurry to move to a smaller house. So i will not take it to a mechanic because of it's low price. It ran real rough and barely made it the 40 miles to my house when i got it. But boy does it have power.

Edit: I started it last night and when it throttled up it smoked, and then shot gas out of the tailpipe. I know it was not oil because it burned instantly when i lit it with a match. This thing is such a boat anchor right now.
Oh and i live in chicago.
Last edited by Yamahas rock on Fri Feb 08, 2019 8:17 am, edited 3 times in total.

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Re: very strange Virago 920 issues

PostAuthor: bstig60 » Wed Feb 06, 2019 6:30 pm

Sounds like a vacuum leak. Who did the carbs and what did they do to them? As far a rejetting, its a hit and miss proposition. Try going up a couple of sizes to start with. Then check your plug color... JetsRus is a good source for Hitachi jets... So I am told.
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Re: very strange Virago 920 issues

PostAuthor: Flyingdog » Thu Feb 07, 2019 10:17 am

:yup:

Yamahas rock wrote:without being given any throttle what so ever it goes from 1000 rpm to 3000 and if I turn off the choke it dies.


To me, that says your bike is seeking fuel. Specially it dying when you shut off the choke. At that point you're cutting off what fuel "is" being feed to the carbs. The choke system on these bike is not like lotta other bikes, meaning it's really a whole fuel delivery system of it's own. Why they call it "starting enrichment" system. Pulling on your lever, you're actually opening a circuit that "delivers" more fuel, rather than cutting off air as with most chokes. For starting cold engines. Bottom line..that's why you're bike is running, cuz it's getting fuel from this enrichment system. Where you should be also getting fuel from the pilot circuit. So...IMHO: a good carb cleaning, checking slider/diaphragm, pilot circuit ..everything should be spotless and all passages open..would go along ways. Make note of what jets are installed. Very possible you might not have to re-jet. Little tweak'n with the pilot screw/jet needle might be all that's needed. Gotta start some where. Might as well start off with a clean/functional carb.

Might want to add a general location in your description. That could effect things, also.
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Re: very strange Virago 920 issues

PostAuthor: Yamahas rock » Thu Feb 07, 2019 11:26 am

i rebuilt the carbs and replaced the pilot screws and screw seals, float bowl seals, needles and needle seats and I completely disassembled and split the carbs and put them in a sonic cleaner. I did not change the jetting. it has a 124 main and 41 pilot in both of the carbs.

"Sounds like a vacuum leak. Who did the carbs and what did they do to them? As far a rejetting, its a hit and miss proposition. Try going up a couple of sizes to start with. Then check your plug color... JetsRus is a good source for Hitachi jets... So I am told."

I do remember one of the intake manifold seals that went from the carb to one of the heads is mangled. I let it be and did not think it could cause a vacuum leak. I am going to look at the carbs tonight so I will look at it then.

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Re: very strange Virago 920 issues

PostAuthor: Yamahas rock » Thu Feb 07, 2019 11:36 am

Flyingdog wrote::yup:

Yamahas rock wrote:without being given any throttle what so ever it goes from 1000 rpm to 3000 and if I turn off the choke it dies.


To me, that says your bike is seeking fuel. Specially it dying when you shut off the choke. At that point you're cutting off what fuel "is" being feed to the carbs. The choke system on these bike is not like lotta other bikes, meaning it's really a whole fuel delivery system of it's own. Why they call it "starting enrichment" system. Pulling on your lever, you're actually opening a circuit that "delivers" more fuel, rather than cutting off air as with most chokes. For starting cold engines. Bottom line..that's why you're bike is running, cuz it's getting fuel from this enrichment system. Where you should be also getting fuel from the pilot circuit. So...IMHO: a good carb cleaning, checking slider/diaphragm, pilot circuit ..everything should be spotless and all passages open..would go along ways. Make note of what jets are installed. Very possible you might not have to re-jet. Little tweak'n with the pilot screw/jet needle might be all that's needed. Gotta start some where. Might as well start off with a clean/functional carb.

Might want to add a general location in your description. That could effect things, also.

What i think may be happening is that the choke system is adding too much fuel after a couple minutes. This causes it too much fuel to go in the motor and it then throttles up. The extra gas then shoots out the tailpipe. I think I will mess with the needle position and pilot screw position.

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Re: very strange Virago 920 issues

PostAuthor: Flyingdog » Thu Feb 07, 2019 11:47 am

Yamahas rock wrote: intake manifold seals that went from the carb to one of the heads is mangled. I let it be and did not think it could cause a vacuum leak.


Big Time leak..probly the #1 cause of leaks in 90% of the bike around.

OEM jetting on your bike is: #1=#126, #2=#128....that's off right there.

Crappy manifold, non-stock exhaust, wrong jetting....that'll do, all right

I think it's opposite of want your thinking. If that were the case it wouldn't die take'n off the choke.
Adding more fuel, as you say, won't make your rpms shoot up, unless you adding air too. But, as you say, you're not touching the throttle. No way..it would just choke out.
If you're seeing fuel shoot'n out the back..you got a problem with your float. Good luck.
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Re: very strange Virago 920 issues

PostAuthor: Yamahas rock » Thu Feb 07, 2019 12:48 pm

Thankyou everybody for responding. I thought that the motor was crap with only 18000 miles which pissed me off. If i can't fix this than it is going to a mechanic as i don't have tons of time to mess with it. I should have left it be when I had it running good. But i thought it sounded like a vacuum cleaner so i stupidly swapped the pipes. My other bikes are a 95' fz09 that i have owned since new and an 07 strait piped Royal Star.

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Re: very strange Virago 920 issues

PostAuthor: Flyingdog » Thu Feb 07, 2019 2:50 pm

Hell..might not be a big deal. New manifolds, make sure the pilot circuit is clear, adjusting pilot screws (2 1/2 turns from soft seat for a starting point), could run just fine. Least enough to get a decent plug read to know where ya gotta go for jetting.

As Bill said..could be a nasty leak. (check everyplace with some carb cleaner) Or...the carbs are still dirty. Gotta remember, jets will have nothing to do with an idle'n problem. You check the air filter and passage to carbs? Do you know how long this bike sat?
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Re: very strange Virago 920 issues

PostAuthor: bstig60 » Thu Feb 07, 2019 4:52 pm

If the engine was smoking white smoke and spitting fuel out the exhaust, you probably have a crankcase full of fuel caused by a stuck float. Check your oil level, if it is over full, open the filler cap and take a smell. If it smells of gasoline, change your oil and make sure you get the stuck float fixed before you run the engine much again.
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"It´s a friggen motorcycle, it´s not supposed to be comfortable, quiet or safe. The wind noise is supposed to hurt your ears, the seat should be hard and riding it should make you s**t your pants every now and then. "

Please take the time to edit your profile to show your location. City, State/Province and Country. It is easier to help you if we know where you are.

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Re: very strange Virago 920 issues

PostAuthor: Flyingdog » Thu Feb 07, 2019 7:07 pm

Yamahas rock wrote: It ran real rough and barely made it the 40 miles to my house when i got it. But boy does it have power.



I don't get this.
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Re: very strange Virago 920 issues

PostAuthor: Yamahas rock » Thu Feb 07, 2019 8:11 pm

Flyingdog wrote:
Yamahas rock wrote: It ran real rough and barely made it the 40 miles to my house when i got it. But boy does it have power.



I don't get this.


I meant it ran choppy and was very hard to start when i got it but when i eventually got it running good and it really feels fast. even though it is kinda slow.

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Re: very strange Virago 920 issues

PostAuthor: Yamahas rock » Thu Feb 07, 2019 8:15 pm

Oh, I found why it was spitting gas out the pipes and throttling up by itself. One of the idle jets came unscrewed and fell into the float bowl. I opened it up and there goes a jet. So that's part of the issue fixed. now it just needs jeting, fork seals, and brake lines and it is good to go. so for $150 it's a steal.

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