Help troubleshooting throttle sticking @5000 rpm

[Nessism]

I think you're saying that at some point the o-rings no longer continue to flatten and it's the manifold that takes all the torque. At some point that is probably true but when you reach that point, you've gone too far in my opinion. It's not necessary to make a good seal.

That's exactly what I'm saying; the amount of O-ring compression is set by the depth of the groove in the manifold. Once a nominal amount of torque is applied to the bolts, the aluminum manifold insert will be in full contact with the head and the O-ring will be in full compression. Continuing to torque the bolts will stress the threads in the head, and stress the manifold, but will not result in any more O-ring compression.

Regarding fastners in general, when compressable elements are involved (such as a rubber washer for example) special precautions, such as thread locking agents and/or mechanical saftey locks (cotter pins), are required or the joint wil loosen as the compressable element creaps with time. What i'm trying to say is that we WANT that O-ring to be fully compressed within the manifold groove such that it is not affecting the clamp load on the screws. Otherwise, the screws will loosen with time as the rubber compresses - not good.

Don't mean to go against you here Keith, just want to clarify. Keep up the good work with all your great carb threads. \\/

 

[Jagir]

I think Mr.Krause wins a prize again. Thank you for not letting me give up on the air leak idea.

I replaced the screw hose with one that has a more positive seal. Took it for a short ride (just past where the throttle hang usually happens) and it ran beautifully. Just need to really test it to be sure.

In this case, I cannot blame the PO. I was away for the weekend when my father-in-law and the mysterious petcock fairies visited my bike. I found a shiny new manual petcock and a hose going nowhere with a screw hanging out. I was reassured that it was fine and that hose just needed to be plugged.

Just to get to the troubleshooting phase, I did enough work on the bike to feel confident and able to diagnose (with GSR help, of course) a host of issues that I hopefully won't have.

The o-rings are pretty new, they replaced the squished flat 25 year old ones. I bought a second set so they can be swapped any old time.

thanks again
I'm going riding. \\/
j

 

[MelodicMetalGod]

Sounds like an air leak was at issue and that you've cleared the issue. Glad to hear it.

My bike has been doing the same (high idle after warm up). I expect to have the new boots and o-rings on by this weekend. Hopefully a few days from now we're both busy riding without worrying about 4-5000 RPM idling at stop lights. [-o<

Enjoy the road!

 

[KEITH KRAUSE]

I think Mr.Krause wins a prize again. Thank you for not letting me give up on the air leak idea.

I replaced the screw hose with one that has a more positive seal. Took it for a short ride (just past where the throttle hang usually happens) and it ran beautifully. Just need to really test it to be sure.

In this case, I cannot blame the PO. I was away for the weekend when my father-in-law and the mysterious petcock fairies visited my bike. I found a shiny new manual petcock and a hose going nowhere with a screw hanging out. I was reassured that it was fine and that hose just needed to be plugged.

Just to get to the troubleshooting phase, I did enough work on the bike to feel confident and able to diagnose (with GSR help, of course) a host of issues that I hopefully won't have.

The o-rings are pretty new, they replaced the squished flat 25 year old ones. I bought a second set so they can be swapped any old time.

thanks again
I'm going riding. \\/
j

Glad it's running better.
Just for the record, Nessism first suggested an intake leak, before I even read this thread. Maybe I helped you some but give credit to whom it's due.

 

[KEITH KRAUSE]

Nessism, we all have our opinions so I don't consider it "going against me".
I'm not exactly sure what you describe in saying "aluminum manifold insert". The manifold-to-head surface is flat, at least the manifold I have in my mind, and it very often has a thin rubber film extending into the outer portions of this flat surface also. Some have more rubber on the face than others, some have none. They are commonly different. If your design in mind is different, then we're not talking about the same thing and everything changes.
Remember, it's just my belief that you can shorten the service life of the o-ring by flattening it more than what's needed to make a good seal. I can't actually see the o-ring compress and see what happens. I think approx' 6 ft/lb is a little beyond the needed torque but then the o-ring will continue to seal even with some "settling" of the parts resulting in a little less torque over the years.
I've seen many o-rings over the years and some removed ones are obviously flatter than others. Most people over-tighten hardware in general, especially hardware that should be torqued at under 10 ft/lb. It seems to me that if the o-ring stops compressing before the manifold bolts are adequately torqued, then every used o-ring would be equally flattened regardless of how much torque was applied. I really doubt that any difference is from under-torquing. An o-ring with a "built in compression limit" would always flatten the same. So I believe that the o-rings that are flatter (and always cracked more) are torqued more than necessary.
Also, I believe the largest manifold bolts are 6mm and they are rated "standard" bolts. The factory recommended torque for 6 mm standard bolts is actually 5 ft/lb max'. If I'm wrong and the largest bolts go up to 8mm, then the factory torque range is 6-10 ft/lb for 8 mm bolts only. In many manuals, they don't specifically say how much to torque these manifold bolts so you have to read the chart.
I actually didn't come up with the "6 ft/lb" torque recommendation myself. It was many years ago that I read an article that specifically mentioned how to torque manifolds and head gaskets. On our style of manifold, it recommended 6 ft/lb. That doesn't mean it has to be exactly 6 but 6 was considered "just right". I no longer remember where I read the article and I don't always believe what I read, but I think it was right and I've always used the method and had no problems.
It's just my opinion. I'm not always right either. I only suggest things if they've worked for me. If someone wants to go beyond the torque I suggest, or the torque the bolt is rated for, then it's their bike.