1979 XS 750 triple, runs for a little while?

Hi all. I purchased a 1979 XS 750 for 50 bucks a few months ago. Thing was sitting for ages. Put a battery and new plugs in it, got a key cut, went thru hell to title it, got it to run, but I am having a few problems with it.

First, it never fires up with the electric starter, just cranks and cranks and cranks. No biggie, it starts first kick, but still wondering why it wont run off the electric?

And then the bigger problem(s) is that once it does start, it seems to run OK. It idles decent, revs up fine. Didnt expect perfection for the price...

BUT...this thing will not stay running more than five minutes. And that five minutes can only be achieved if its sitting by itself idling. I took it for a ride and it ran even shorter than that. It just abruptly died in the road and I had to walk the big heavy bear back home. Its not like it warns you and starts running poorly, its just there and then gone. You can kick all you want, it wont restart.

Then I can come back to it an hour later, and starts first kick again. Dies 5 minutes later again.

Any thoughts? Thanks!

 

Re: 1980 XS 750 triple, runs for a little while?

sticking carb bodies and not used during idle cycle so the beast dies under load.or possibly sticking float needles, but the electric start now that is a good one. gotta ponder that a bit.........hmmmmmmmmmm

 

Re: 1980 XS 750 triple, runs for a little while?

Engine cranks but won't fire and it'll start with kick starter is an electrical problem. Either there isn't enough voltage when cranking to fire the coils or someone re-engineered the coils to ground through the starter circuit. If it doesn't look hacked up I'd guess poor battery or dirty electrical connections.

Runs for awhile then quits is usually a fuel issue. Check to make sure the filter(s) aren't plugged and the fuel cap vent is open.

 

Re: 1980 XS 750 triple, runs for a little while?

If it's an XS750 it's probably a 79 titled in 80. They were only made 76-79. Then it was an XS850 triple for 80 & 81.

Make sure the headlight isn't on when trying to start it. If it is, the lighting relay contacts might be welded together.

Need to check the charging system and battery. Take apart and clean every ground from the battery to frame to engine. Check the positive from battery to solenoid to the starter. Had a friend who had the same problem with his XS850 and it was the grounds and battery. Every connection he cleaned helped pick up the voltage a fraction or two. He also replaced the tailight with an LEDs which also helped pick up his voltage to the starter. Might have to take apart the starter and check/clean the brushes and commutator as it might be all carboned up.

Have you've already pulled the carbs, cleaned them and reset float heights ? It sounds like a low/loss of fuel problem. With it dying every 5 minutes it could be the fuel tank vent is clogged. They like to rust up but can be cleaned out. You just have to disassemble the cap.

A good resource : Yamaha-Triples.org

Richard

 

Re: 1980 XS 750 triple, runs for a little while?

hey richard thats a good link and timely info. thanks for chippin in,and micarl as well u guys are the best!!!

 

Thanks everyone, those are some good things to look into when I get a chance.

Probobly should have said what I have already done...

I already took off the carbs, cleaned and reset the floats. Other than that I didnt mess with them in any other way. My knowledge of carbs is limited at best. I have a clymer on the way.

Battery is new. Electrolyte level is good. Battery tests good. Also have tried cranking it on a car battery with the same issues. Ill look into cleaning/replacing the grounds tomorrow. Headlight doesnt come on during cranking. I should also mention that it cranks over very strong.

I wasn't aware of a fuel tank vent, Ill look at that. Seems like that might be it. Because its not that it dies under load or any particular condition, its just almost like a timed thing...

We can hope, because I wanna ride this thing before the snow! I love the thumpy sound it makes! Very unique!

Oh and yeah...I boogered up the year, its a 79! I always think my bikes are a year newer than they are. I was calling my XJ an 82 for the longest time. :roll:

 

I had a car that would do that sometimes. It would just shut off mysteriously. If you came back an hour later, it would run great. Sometimes for a few hours, or a few weeks. Turned out to be sediment in the gas tank that was occasionally getting sucked into the pump. When it drained back out, it would run until getting sucked up again. I would agree with the others. It's dirt or rust or something somewhere in the tank, petcock, or carbs.

 

Quick question on the tank vent. Would running it with the fuel door open work to fix that problem? I'm not saying as a permanent fix, but just long enough to be sure its a vent problem...

Bike is stored far away so figured id ask to be sure...

 

I have a 77 and 79 XS750. With weak batteries mine would do the no start problem but fire easily with the kick starter. After starting they would always restart with the electric starter. I have installed glass mat batteries in both and no longer have a problem. The starter pulls a lot of current but I'll bet new coils or cleaning coil connections would be another cure for the problem.
By the way, my 79 is probably my favorite vintage ride. Growls like a bear, pulls like tractor and is a delight to look at! (I have the standard).

 

peewee, That would be one way to test it.
Might pull the starter, disassemble it, check brushes, and clean it.

yamasarus, gotta luv the vintage ride and sound of the Triple Eh!

 

rpgoerlich,

Yes, I love my vintage Yamahas. I am really into the 77 and older 650 twins, but if I had to ride a long way on a vintage Yamaha, it would be my 79 Triple. I just had my 77 Triple out yesterday. You don't need to go 150mph to really enjoy a motorcycle.