Help diagnosing problem with GT750J needed

[2STROKECAFE]

Gentleman,
I have a friend that's having the following problem with his 72':

Bike starts no problem runs choked, but stalls when put into gear (makes that running out of gas noise) it looses power to the point that it can't be driven.

He's took the bike to a shop here in MA and had the following work done since first experiencing the problem, but is still having the same issue:

All three carburetors cleaned & rebuilt.
Tune up done & all points and condensers were replaced.
Outer crank oil seal replaced.

Needless to say he's pretty frustrated & isn't willing to take it back to the same shop (long story, many other issue involved).

Any ideas? Any help would be greatly appreciated.

Thanks & take care,
Bryan

[2STROKECAFE]

Forgot to add, 74 engine in 72 chassis. Fairly low mileage.
Thanks & take care.

[djfisher22]

Don't know how much this will help,but my bud just finished his build on a 74 buf and it would only run on choke. He brought it to my house and we just systematicly went by the book with carb sync and then set the timing to specs and it runs great now. Nothing big was wrong. If a shop did the carbs they may just need set up correctly. Sometimes it's just the little things.Start with the cheapest solution and work up from there.

[Barry S.]

The petcock has a vacuum hose to open it up when the motor is running, the diaphram may be bad or it may not be hooked up at all, check it out, also has a screen that may be stopped up.

[pjmcburney]

Gentleman,

Outer crank oil seal replaced.

Hmmm... what the heck is the 'outer crank oil seal' and how/why was it replaced?


None of the crank seals are able to be 'replaced' unless the cases are split.
The outer-most seals are retained by a deep groove in the cases and they cannot be removed and replaced like a simple tap-in lip seal found elsewhere in the engine, and (as a matter of course) the inner seals are well, inner and require not only the cases split, but the crank dismantled.
Besides, even if the crank seal/s were shot, the bike would still run ok and shouldn't exhibit the symptoms described.

Carbs can be set quite accurately by eye on the bench. Ensure all three butterfly valves cover/uncover the same bleed hole in the venturi wall (where the edge of the valve touches) at exactly the same time.
Also ensure the float heights are correct and identical.

Turn the petcock to prime and try running the bike like that to ensure fuel is flowing freely - if things improve check the petcock for correct operation in vacuum 'mode'. If the vacuum diaphragm is damaged or installed incorrectly it may not let fuel flow.

And as stated by others, check the timing and points again. If the dude at the shop can replace an 'outer crank seal', who knows what he's done to everything else.
It's no wonder he's reluctant to return the bike to that shop.


Good luck
Paul

[tz375]

Just to add to Paul's comments, my experience with shops doing carbs is that they are often worse than those of us that do it at home.

It's an incredibly time consuming fiddly job and if Coyote Chris's experience is anything to go by, they rarely get the synch even close.

Start with the basics and get those right first.

[2STROKECAFE]

Thanks so much for the feedback guys. I'll pass the tips on & let you know how it goes.
Thanks again,
Bryan

[oldjapanesebikes]

Here's another simple thing to check as I've done this to myself I installed a new in-line fuel filter and new clear fuel line hose - the filter was a bit long and I didn't notice that the line had a very slight kink on the fuel petcock side leading to the filter which starved it of fuel. Started OK, ran for a few minutes, and then the engine slowly died off the same way you describe. Possibly just something else to look at.