Throttle gets stiff when bike is hot and parked.

[Meraco]

I noticed a new peculiarity with the throttle.  1988 FJ 1200.

After riding for about 45 minutes and the engine is hot. I parked for about 10 to 15 minutes. When I went to resume riding, I found that the throttle was sticking and needed to be pushed closed to idle. It was as if I had cruise control.

After about 8 minutes of riding the throttle was back to normal operation.
It does not stick when fully cooled down. New day start up. (full unrestricted snap back.)
It does not stick when riding for any length of time even city and hot.  (full snap back.)

But if I stop and wait about 10 to 20 minutes and go to get back on. The throttle sticks.  This has been reproducible.

So this indicates to me that there is some sort of expansion happening due to high heat during a stop. But then clears itself as it cools down.

Any ideas?

- Butterfly valves?
- cable?
- Spring?

[Pat Conlon]

That's an interesting problem. I don't recall that ever coming up on the forum. I think you're right, expansion due to heat. It's a hot environment under the tank so that's where I would focus. I assume you have the oem heat shield in place. Is there a dry spot in your push pull cables that binds when it heats up? These cables run over the top of the engine, the hottest part of the bike. I would pull your cables, clean them and lube the crap out of them.
Is the carb linkage binding up when hot? I would take a heat gun and heat things up, see if you can replicate the problem.  I assume your throttle tube is clean and lubed.

I hope Robert at RPM chimes in, perhaps there is something internal in the carbs that could cause this?

[RPM - Robert]

Nothing to bind internally that I can think of. I have seen them slow to return when there is a bunch of crud (dirty gummy dried ethanol fuel) in the throttle shaft seals from sitting for years, but once hot that would go away.

Are you sure the throttle tube on the right handle bar didn't get bumped and moved? Also, can't remember who but they had one of the pinch type cruise controls on the right tube and it had worn through and was causing the throttle to stick.

[Sparky84]

Nothing to bind internally that I can think of. I have seen them slow to return when there is a bunch of crud (dirty gummy dried ethanol fuel) in the throttle shaft seals from sitting for years, but once hot that would go away.

Are you sure the throttle tube on the right handle bar didn't get bumped and moved? Also, can't remember who but they had one of the pinch type cruise controls on the right tube and it had worn through and was causing the throttle to stick.

I've had the grip slide to outside and grip on the end bar weights, which stopped throttle from returning all the way

[Meraco]

Thank you for clues on where to look.

As time passed I was still able to recreate this specific issue.

During a cold start the throttle had normal operation. It snapped back when released.
During riding it was also working as intended, no sticking would occur.
But if the bike was hot. the throttle got stiff and eventually would stick in position.

So to me this meant it must have been on the hot side of the throttle assembly. Or so I thought...

Took it to a mechanic who works on vintage bikes, and we began to search the problem. ( the bike was cool and the throttle functional at this stage) We started with the basics. cleaning and lubing the 4 cables. opened up the throttle harness and put new grease. We also lubed the throttle bar that runs along all 4 carbs.

This seemed to improve the response of the throttle handle.

So I then took it for a ride to see if I could heat up the bike and recreate the problem I originally had.  Mostly city riding light to light to heat it up quickly.

I then stopped and waited a bit. and nope. the dern throttle got stuck again.

So I rode back to the shop and showed the mechanic the issue persisted. I asked him.. whats the next move? another carb kit and removal? even though it was done last year already.

He paused for a moment and said. Lets check out the throttle handle itself. I was so skeptical.. how could it be that.. surely the heat being the cause could not affect the throttle handle.

So he removed the end weight. and to my surprise the throttle was now completely free, even though the bike was hot. I was beside myself. How the hell can it be that??

So he fabricated a spacer and put the weight back on. and it all works now as its supposed to.

So you guys were spot on with the handle being the issue. Even though I originally brushed it off with all focus being the heat that was causing it. and it only happened when it was hot and sitting. So I am still confused about how the heat from the engine while stopped would introduce the problem in an area that was nowhere near the heat... baffles me.

Thanks again guys.. going forward I will differ to your experience and try your suggestions first. even when I think " nawww cant be that "






 

[Old Rider]

I had the same problem it is easy to fix by using some silicone spray at the pints in picture

[Old Rider]

By the way nice FJ you got there i notised the front fender is not original is it a gpz 600r fender ?
And if i remember right i think you can just move the hole throttlegrip and the electrical assembly further away from the bar end.

[Meraco]

By the way nice FJ you got there i notised the front fender is not original is it a gpz 600r fender ?
And if i remember right i think you can just move the hole throttlegrip and the electrical assembly further away from the bar end.

I am not sure what fender was used as I bought it as you see it in the picture. It may be the gpz 600r.
I should have asked at the time I bought it. All he said was that he had to McGeiver it on.
The previous owner had the bike for 27 years and stored for the most part.

I did post a request to see if anyone knew where I could get an original since my searches did not result in finding one. There were some suggestions and offers. But from what I saw they were used parts and not in the best of condition.

I will also keep your suggestion in mind should the throttle act up again. Thanks.