:: Yamaha Virago XV Forums That Rock!!! XV750 '81 xv750 won't fire (SOLVED)

#1:  '81 xv750 won't fire (SOLVED) Author: scrow Post Posted: Sun May 23, 2010 2:56 pm

I was given a virago over a week ago and I've spent a lot of time researching and working on the bike to get her running. I have read many threads where people have been helped so much by this forum, so I'm hoping to benefit in the same way.

A little about the bike:
Mostly garage kept, 50,000 miles on the bike, looks like it has been maintained well by the one and only previous owner. He did most of the work on the bike himself.

This is what I've done so far:
-New battery - fully charged
-Cleaned the carbs - probably the first time the carbs have been thoroughly cleaned (other than the float bowl), i did not break open the pilot adjustment chamber yet
-Rebuilt the starter solenoid (after it stopped working on me - took it apart - looks like the copper contact area was not allowing good conduction)
-Compression test on both cylinders around 130 psi
-Using old spark plugs checked for spark (spark is present but it may be weak - not sure the difference between a weak and strong spark)
-Installed new spark plugs
-The starter motor cranks the cylinders (obviously if i was able to do a compression test)

Okay when I try to start the bike it won't fire. So i tried to push start it to see if it would fire that way. The push start yielded a few put, put, puts but did not start (I was pushing by myself so i probably didn't go fast enough)

Here are my thoughts thus far, perhaps the spark is not strong enough and the ignition system connections or caps need replacing or cleaning. Or perhaps the infamous bendix spring clip is not stopping the gears to allow them to pull away from the flywheel. Or perhaps the starter motor is slipping under larger loads and will not spin the flywheel fast enough to get the engine started.

After i tried 8 push starts or so with the new spark plugs i removed the pugs and found fuel on the plugs. So i know I have some spark, decent compression, and fuel. Lastly I keep reading about the o-rings on the carb manifolds. The manifolds were recently replaced by previous owner, but there were no oring in the groove of the carb output (engine intake). There are only cable clamps. Could a leak at the manifold not cause the engine to fire? I should probably get orings if I can does anyone know the size of these orings? Thanks in advance...

Last edited by scrow on Tue May 25, 2010 8:55 am; edited 1 time in total

#2:   Author: anaman51 Post Posted: Sun May 23, 2010 4:39 pm

Yeah, you're gonna need those O-rings. The dealership can order them for you for $6.26 apiece. A vacuum leak can cause all sorts of troubles, but there's a good chance your battery ground is part of the problem. These older models had a lousy ground from the beginning, and you need to install a second ground with the same size cable or larger. It needs to be fastened to a bolt in the steel frame, with the paint cleared away, to be a good ground. There are places under the seat and behind the battery to do this. I used an automobile 4-gauge starter cable to do it, and it worked great. That should improve your spark considerably, and then give it another try.

And welcome to Virago Tech! Thanks for filling out your signature!


#3:   Author: totallyredvirago Post Posted: Sun May 23, 2010 7:43 pm

some manifolds dont have the "o" ring. does yours have the gasket instead? if so then no "o" ring is needed..
are both plugs wet? or just one? weak spark will be a yellowish color.. a good spark will be a white/blue.. what color are yours?
welcome to vt...dan

#4:   Author: pofarm Post Posted: Sun May 23, 2010 8:03 pm

The O rings are located between the intake boots and heads, not the boots and carbs. Some of the earlier ones used gaskets instead of O rings.

#5:  Re: '81 xv750 won't fire Author: scrow Post Posted: Sun May 23, 2010 9:43 pm

There is a gasket between the mounts and the engine, but only a hose clamp on the carb/soft side of the mounts. I thouht there might have been an oring in addition to the clamp since there is a groove in the OD of the carb output. So I guess I am okay with the mounts. The color of the spark is blue but it seemed very thin to me, but it defenitely was not yellowish. I think both plugs were wet, I will have to double check tomorrow. So I guess I need to add a better ground bond. I will do that first then try another start. Do you guys think the starter and associated mechanics could be hanging up the firing?

#6:   Author: pofarm Post Posted: Sun May 23, 2010 10:46 pm

The TCI needs as much voltage as it can get. The starter pulls quite a bit. Make sure all wiring connections are clean and tight. Get some contact cleaner and pull apart the connectors. Spray them with the cleaner and plug them back together several times. The TCI is mounted under the gas tank. Make sure you get all the connections to it cleaned.

#7:   Author: anaman51 Post Posted: Mon May 24, 2010 12:09 am

Anybody know which years had O-rings and which had the gaskets? I had thought the O-rings were a Hitachi thing, but those are the only ones I've had contact with. It'd be nice to know which was which.


#8:   Author: club_c Post Posted: Mon May 24, 2010 1:00 am

In these types of cases I've dribbled a little gas straight into the plug hole to get fuel in there, whipped in the plugs and tried a start up. If you get it firing strong, then you know youve still got carb work ahead of you. Any reason to think cam timing may have been fooled with by the PO or you?

#9:  Re: '81 xv750 won't fire Author: scrow Post Posted: Mon May 24, 2010 8:16 am

Regarding the timing I guess anything is possible (I know I didn't mess with the timing), I can look into that if nothing else works. I'm going to try some starter fluid in the engine as well to see if I get a fire from that...

#10:  Re: '81 xv750 won't fire Author: scrow Post Posted: Tue May 25, 2010 8:54 am

Okay, here is an update... Last night I took your suggestions and started off by adding a 4 AWG grouding wire from the battery to the frame nearby (I'll try and post some pics later). Then I tried to add some starting fluid to the cylinders to see if it would fire, which did not work. So perhaps the ground wire helped a little, but still no fire. Then I completely broke down the ignition system and cleaned all the connectors with electrical contact cleaner and compressed air. I even took out the ignition coil modules and cleaned the connection of the plug wires at the ignition coil and spark plug caps. One connection on the ignition side of the plug wire looked like it did not make as much contact with the needle inside the ignition module so i pushed the ferule back a little to add more engagement. Also one connection on the cap side looked a little worn so I cut the plug wire 1/4" shorter and re-threaded the connection there. Then I installed everything again hoping the cleaning would solve the issue. Crank, crank, crank.... no fire... It was 9:30 PM so I went inside wondering what the issue could be. As I was about to jump in the shower I thought about the two connectors at the ignition coil modules and did not recall that I had re-connected them. So I threw on some clothes and went out to see. I Had Forgot To Connect Them... So I pushed them together and hit the start button. Crank FIRE... she backfired. The first sign of life out of here in about a year. So I tried again this time with the choke On, crank fire and she started. Yeah!!! I tried to warm her up so I could turn off the choke to see what RPM she idled at, but could not. I think my petcock may need a look at and will have to check for vacuum leaks. Either way at least she fires... I'm going to consider this post Solved since the initial post had "won't fire", and now she fires, but probably with other problems. Thanks guys for your help... XV750 '81 xv750 won't fire (SOLVED)

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