Wellington mechanic for 1981 XV750 Virago with an intermittent fault?

[tourist76]

Bike located in Miramar but can be ridden or dropped off anywhere in Wellington. I am Seeking a mechanic who knows these bikes and is happy to do a perky, to try figuring out what is wrong. I have gone through and checked/ replaced everything I can think of, now its time to hand it over to someone else who may be able to figure out what is wrong. Here is a list

1981 yamaha virago xv750
Bike starts and runs fine
Once riding for 'a while' there is an Intermittent failure on one OR the other cylinder, after riding 5-50km (yup its a wide range). The bike just starts to gradually cut out on the cylinder it chooses, until a complete cylinder shutdown occurs. Once one cyclinder fails, the other goes for a few more kilometers, then may also fail. Once the bike dies, it will not start for 10minutes to an hour, then fine to start and ride again.

Work done to try and identify the problem:
-spark plugs changed
-coils both replaced
-coil leeds replaced
-rust treated the tank and Por-15 recoat
-petckock/regulator valve kit replaced incl diaphrams (valves cleaned)
-fuel lines and filters to the carbs replaced
-carbs cleaned incl needles etc and carbs balanced
-clear tube method check done to check carb refil function
-main fuse box (with Yamaha on it) under the headlight changed
-replaced the TCI/CDI under the fuel tank
-replaced the pickup sensor (under the Yamaha left side engine cover)
-battery good and not draining
-cyclinder pressure reading is (from memory) normal and definitely even between cyclinders.

[caseye]

When you find this mechanic, please make sure you wrap em in cotton wool and then post em up to Dorkland, I'd love to have a mechanic that really does know what they're doing with these engines.
Ask ol Crasherfromwayback, if anyone down there does know such a beasty it'll be him.
BUTT! don't accept his coffee. K? got that very clear now , have we???

[Akzle]

id be looking at those coils again. Did you find aftermarket or just use wrecker/ed ones?

[tourist76]

Borrowed em of a wrecked bike, no access to other ones that i know of

[T.W.R]

Could be the fuel tank isn't venting properly.

Early XVs were jetted lean also more so TR1s but 750 Virago is American spec name of the original XV

this a in-service report I posted 8yrs ago

http://www.kiwibiker.co.nz/forums/showthread.php/31714-Yamaha-XV-in-service-report

[FJRider]

Were the high tension (to the plugs) leads changed when you changed the coils .. ??

CDI unit .. ???

The good news is ... its either fuel or electrical ... :innocent:

[Mo NZ]

Could be the fuel tank isn't venting properly.

I had a similar thing with a twin.

Turned out to be a tip-over valve sticking, which also vented the petrol tank.
If I loosened the petrol cap when it began to shut down, it started running fine.

When I say loosen the cap it is to allow air to enter the tank and release any vacuum inside the tank caused by a faulty vent setup.
Once vented re-secure the cap.

[hayd3n]

did you install a free flow fuel filter?
or a cheap high pressure one one from ripco etc

as im to assume the bike is gravity fed?

because if its a high pressure filter it will cause a hell of a lot of strain on the flow and almost stop all fuel flowing

i made myself a filter out of some brass fitting and and super fine stainless steel mesh
works great

[tourist76]

Thank you,

10 months into trying to identify the problem and gradually going through and checking every suggestion I came across, we strike gold.
I have found that the tiny ball bearing inside the valve in the petrol cap, had rusted. Thus shutting off the air and creating vacuum in the tank. This problem would arise only once riding for a while. I believe this was a feature designed to comply with Californian regulations, to prevent 'copious amounts' of fuel leaking out through the pinhole size venting valve, in the petrol cap. if the bike were to be dropped, the ball bearing would shut off the fuel leak.
The owners manual does not seem to mention this 'safety feature' but with the help of the good people I finally found the problem.

Thank you to the great folk on kiwibiker.co.nz here in New Zealand and virago.com fellas in the states and world wide for all the advice. thanks heaps to the kiwi motorbike guru Jim Dougherty who lent time, parts and advice, and of course my good friend Sergei Bolotnyani who spent countless hours going through the bike with me. Could not have done it without your help. Thank you!

[jellywrestler]

Thank you,

10 months into trying to identify the problem and gradually going through and checking every suggestion I came across, we strike gold.
I have found that the tiny ball bearing inside the valve in the petrol cap, had rusted. Thus shutting off the air and creating vacuum in the tank. This problem would arise only once riding for a while. I believe this was a feature designed to comply with Californian regulations, to prevent 'copious amounts' of fuel leaking out through the pinhole size venting valve, in the petrol cap. if the bike were to be dropped, the ball bearing would shut off the fuel leak.
The owners manual does not seem to mention this 'safety feature' but with the help of the good people I finally found the problem.

Thank you to the great folk on kiwibiker.co.nz here in New Zealand and virago.com fellas in the states and world wide for all the advice. thanks heaps to the kiwi motorbike guru Jim Dougherty who lent time, parts and advice, and of course my good friend Sergei Bolotnyani who spent countless hours going through the bike with me. Could not have done it without your help. Thank you!

any relation to Jim Doherty from Lower Hutt?

[tourist76]

any relation to Jim Doherty from Lower Hutt?


Hi, it sure is :-)