XV750 cylinder failure, 1981 Virago

[tourist76]

Hi there, looking for some advice guys. My trusty 1981 xv750 virago is having the front cylinder failures when riding. Runs fine when stationery and for the first couple of miles on the road, then the front cylinder begins to cut out.

Whats been done to try & fix it:
Spark plugs changed (old ones were also fine)
Coil lead replaced
Coils swaped around
Tank clean n reseal
Taps/ petcock seal and diaphrams new
Hoeses check on fuel and vacoom
Fuel filters changed
Carbs cleaned and balanced
Problem occurs even when running in pri position so probably not a vacoom issue

[ducatilover]

Do a compression test

[cynna]

my xv400 i had about 20 years ago used to do this. took it to two different bike shops - one said it was electical and the other said iy was the ypis (or what it was called). ended up trading it in - spent a lot of money and never got anywhere.

[unstuck]

Like loverboy said, get a compression test done.:niceone:

[pete376403]

can the carbs be swapped?

[carburator]

Hi there, looking for some advice guys. My trusty 1981 xv750 virago is having the front cylinder failures when riding. Runs fine when stationery and for the first couple of miles on the road, then the front cylinder begins to cut out.

Whats been done to try & fix it:
Spark plugs changed (old ones were also fine)
Coil lead replaced
Coils swaped around
Tank clean n reseal
Taps/ petcock seal and diaphrams new
Hoeses check on fuel and vacoom
Fuel filters changed
Carbs cleaned and balanced
Problem occurs even when running in pri position so probably not a vacoom issue

TCI issue... to run well they need FULL voltage..

[Warr]

Had a similar issue with my XJ900. 80's vintage, but could be you are experiencing a CDI fault as I did.
My easiest advise would be, locate a replacement CDI unit.
The originals are a sealed unit and with time the solder connections inside start to corrode and go 'dry joint'
Because the XJ900 is an IL4 I was able to confirm that 1/2 my unit was faulty.
By swapping the sensor wires and the CDI > coil wires I could swap the fault from 1 pair of cylinders to the other pair.

I opened my CDI sealed unit by removing the epoxy resin and re-soldered the joints. Followed by cleaning the visible parts of the circuit board and resealing the unit.
Fortunately my efforts were rewarded and the fault cleared.

Another option I would recommend, much easier and one I would pursue today would be contact this (http://www.trademe.co.nz/Members/Listings.aspx?member=1517478) Trademe seller to see if he can supply a CDI unit for your bike.

[tourist76]

Forgot to mention compression test already done and all good. Will try the cdi check if i can switch the wires over to the other cylinder. Also will try Check the float level with the clear tube method.

Will keep this thread updated, thanks fellas.

[tourist76]

Forgot to mention compression test already done and all good. Will try the cdi check if i can switch the wires over to the other cylinder. Also will try Check the float level with the clear tube method.

Will keep this thread updated, thanks fellas.




Ok, looks as though the cdi cant be flipped around between cylinders... Going to look for one to borrow so i can make sure, before i throw $250 at it.

[ducatilover]

I'd agree with checking the cdi unit since you've taken all other logical steps

[Theantidote]

have you had a look at viragotechforum ...http://viragotechforum.com/ some of the guys on there really know the xv inside out...and being yanks it's a bit polite...:blink: but worth snooping around

[ducatilover]

Could be worth checking the valve clearances too

[Grumph]

The ignition pickup wiring is known to get faulty with age on those things.
Worth pulling the sidecover and examining the insulation.

[Theantidote]

The ignition pickup wiring is known to get faulty with age on those things.
Worth pulling the sidecover and examining the insulation.

just read about this online and makes some sense...
i'm following this coz i to am having probs with a viagra that's started playing up....

[tourist76]

Hey there, an update on recent checks which were done to try n identify why this 1981 xv 750 (virago) runs great first 2 km then cuts out, has a 5 min rest and ready to go again for another 2 km etc. etc.

Whats been done since the last post:
Carb floats checked using the clear tube method
CDI replaced
Wiring from the CDI to the left engine cover found to be exposed and contacting the metal where it comes out from behind the clutch cover.


Many thanks to all those submitting ideas, going through them slowly guys (have 3 kids that compete for time with the bike :-)
Many thanks to Jim Doherty in Lower Hutt for lending his advice and parts

[tourist76]

Grumph the ignition pickup sensor is the next check, seeing the CDI/TCI unit that Jim Doherty lent me made no difference...
I've got a friend helping out, he is a car mechanic but is quickly becoming a bike mechanic too:wacko:
Ducatilover theantidote and all others thanks for the tips too, we'll check the valve clearances tomorrow hopefully ( why not), just gotta find what they are meant to be. Haynes manual search so far didnt give and answer...strange
She ran for about 7km after i replaced the main fuse board, before starting to cut out, nearly had my hopes up. She usually cuts out after only 2-3 km.

Oh yeah, compression test is good, carb floats fill up nice and quick, fuel system has been tripple checked.

engine pickup coil crank sensor is thennext check me thinks , since the ignitor wire was exposed it may have killed it.

[tourist76]

:gob:
just read about this online and makes some sense...
i'm following this coz i to am having probs with a viagra that's started playing up....

Hehehe, i am trying on virago forum too, lots of ideas,, thanks

[kevie]

I have a XV750 in the shed too ..... rebuilding it as time allows, there's an awesome guy in palmy (Pete king) that's a V twin guru, he rebuilt the motor on mine.

I hunted for diaphragms for it and got some from USA for NZ$54 (including freight) (they were $400 each when Yamaha had them)
also imported in a brand new starter motor from the states for it, cost me NZ$218 including airfreight and was here in 10 days, (Yamaha quoted me $1,400 for one plus freight from Japan and it would be about a couple months arriving) ...... i had an intermittent fault on the bike a couple years ago and the wiring from the ignition pickup was frayed through the insulation where it comes out of the motor casing on the left side of the motor, as a poster mentioned ..... common problem.

just have to refit the carbs and hopefully the beast runs again :) still haven't decided what im gonna do with it yet when its back on the road .... have bought a new bike in the meantime so might be up for sale lol has had $7000 spent on it and $4100 of that was on the motor alone.

[Theantidote]

I have a XV750 in the shed too ..... rebuilding it as time allows, there's an awesome guy in palmy (Pete king) that's a V twin guru, he rebuilt the motor on mine.

I hunted for diaphragms for it and got some from USA for NZ$54 (including freight) (they were $400 each when Yamaha had them)
also imported in a brand new starter motor from the states for it, cost me NZ$218 including airfreight and was here in 10 days, (Yamaha quoted me $1,400 for one plus freight from Japan and it would be about a couple months arriving) ...... i had an intermittent fault on the bike a couple years ago and the wiring from the ignition pickup was frayed through the insulation where it comes out of the motor casing on the left side of the motor, as a poster mentioned ..... common problem.

just have to refit the carbs and hopefully the beast runs again :) still haven't decided what im gonna do with it yet when its back on the road .... have bought a new bike in the meantime so might be up for sale lol has had $7000 spent on it and $4100 of that was on the motor alone.

frig mate that's a huge investment in an ole bike...i'd keep it, recon it back to show room and leave it to my kids...only in 30 or so years might it be worth what you've spent on it - or use the miles for smiles calculation i use - every km i ride with a smile on my face less the gas i put in it = a dollar value based on purchase price and licensing.
so if i paid 2,800 plus 500 for licensing thats about 3,300 = so for every k i ride with a smile i take 3.30 off the original figure...after 3300km's it's all a bonus eh bro...:scooter:
use the same calc with the coffee machine which was basically owing me nothing after 3 weeks of great coffee....

[kevie]

frig mate that's a huge investment in an ole bike..

Yeh when I started the upgrade the cams had crapped out and I did love the bike and planned to keep it, budgeted $3K for the work ..... motor blew out to $4100 so was a point of no return really lol so carried on and tried not to count the dollars lol

within a month of moving to Huntly, i was involved in a car crash which left me with no wheels for work, so went and bought the boulevard ..... so with the change in circumstances, the virago is not that much of a priority now :( so will get it on road and see what happens from there..... keep it in the shed and ride occasionally ...... or cut the monetary losses through the awesome rides i have had on her and sell it, it has done 10,000 on the new motor.

[jellywrestler]

some of those era yams had a rev limiter in the rev counter that cut cylinders maybe this has one that's playing up?

[Theantidote]

Yeh when I started the upgrade the cams had crapped out and I did love the bike and planned to keep it, budgeted $3K for the work ..... motor blew out to $4100 so was a point of no return really lol so carried on and tried not to count the dollars lol

within a month of moving to Huntly, i was involved in a car crash which left me with no wheels for work, so went and bought the boulevard ..... so with the change in circumstances, the virago is not that much of a priority now :( so will get it on road and see what happens from there..... keep it in the shed and ride occasionally ...... or cut the monetary losses through the awesome rides i have had on her and sell it, it has done 10,000 on the new motor.

i gotta say when they go...they go well and are so freakin comfortable it's actually a safety feature having a small tank...if i could when mine runs well i'd be on it all day if i didn't have to stop for gas...good on you for persevering with the viagra bro...hope to see you on the road when the weather clear abit...:scooter:

[tourist76]

Hi guys, been trying this that and the other. Now after a motorbike mechanic who can do this as perky...

[fatboyzed]

Check the bearing surface that the cams run in, no bearings as the cams run in the alloy casting.
Had one with similar problems found the bearing surface had picked up (gouged) and bike would do as you have explained.

[Grumph]

Check the bearing surface that the cams run in, no bearings as the cams run in the alloy casting.
Had one with similar problems found the bearing surface had picked up (gouged) and bike would do as you have explained.

Not quite right - the inner end of the cams run in the head, yes, but this end doesn't give trouble because that's where the oil enters...

The camchain end runs in an alloy bearing block which is known to pick up occasionally. By some fluke....that bearing block is exactly the size and shape of a common ball bearing. Can't remember the number offhand but if anyone has bearing trouble that's an easy solution.

Has Jim got any good spare coils ? Worth dropping a known good one on and trying it out...

[tourist76]

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.

[Grumph]

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.

Okay...I seem to remember reading somewhere that when these things have fuel feed probs it's usually the front cylinder which cuts out first....Out of curiosity, try draining the tank via the front carby drain screw. You've already got the fitting you used for float level checking so it's just a longer hose into a can. Has the cap vent been checked ? Does it do it with the cap off ?

[ellipsis]

...i had problems with mine, fucked around and coughed and spluttered, admittedly I was trying to make it's back wheel spin and get me round a dirt track...fixed it by putting 38mm Mikunis on it, sticking out about three inches from the head on some shit I flanged up...the pipes were inch and a half open...I started off with them poking out past the axle by a foot and shortened them 'til the front wheel was off the ground on load up...fucking crazy, wouldn't idle, but I didn't want that...no use to you or your problem, but it was fun remembering...

[tourist76]

The air intake hose has been checked before and looks how it should. Are you saying to open the tank lid and ride with it open?
I have noticed a hissing sound, coming from the nank,once or twice when the bike stops. Possibly the 2 coats of por15 tank seal have clogged up some valve?

[Grumph]

The air intake hose has been checked before and looks how it should. Are you saying to open the tank lid and ride with it open?
I have noticed a hissing sound, coming from the nank,once or twice when the bike stops. Possibly the 2 coats of por15 tank seal have clogged up some valve?

Most tanks vent through the cap. If it's partially blocked you would get the symptoms you describe.
Either trying to drain it through the carb - with the cap on - or simply popping the cap while riding when it starts to cough will tell you if that's your problem.

Some model Viragos do vent through a emissions catching black plastic box - I've seen reports of those blocking too. If there's one on your bike just pull it and vent to atmosphere.

[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!