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Discussion Starter #1
On my 70 Bonny, I had no problem with a sticking throttle. I had installed hardened slides and had everything moving nicely. A motorcycle guy that truly knows his onions installed an oil pump for me. He obviously had to remove the tank and when he had it all back together and was test riding he commented that I had a sticky throttle. I have ridden it a fair bit since then and the throttle does slightly stick. I seems to only stick in the range of 3000 to 3500 and not in that range in fourth gear. Only at he lower speeds.
Since it didn't start sticking until the tank was removed, I had suspected the throttle linkage was cramped somehow, but since it is so consistently sticking in the same rev range, it sounds more like the carbs themselves.
Has anyone had a sticky throttle like this and what did the problem turn out to be?
Thanks for any help on this. Jim
 

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Hi Jim,
If you have the Amal concentric Carburettor it can be distortion of the carburettor body caused by over-tightening the mounting bolts. The flange bends and twists the carb out of shape.

Check you have the correct carb mounting ‘O’ ring and only nip up the mounting nuts, until the O ring seals, do not tighten it hard down.
I if it has been overtightened, see if slackening the mounting bolts eases up the sticking slide, you might be lucky.

Regards
Peg.
 

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Discussion Starter #3
Thanks Peg., but my carbs worked fine until the oil pump job was done and I don't believe that the the carb manifold would have been removed in that job (but if you believe it did then please say so) and its tightness (or looseness) had already from many hours of use proved to be OK. Jim
 

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Discussion Starter #5
Why was the tank removed?
I did have a small leak somewhere around the pushrod tube that was taken care of at the same time so the tank was removed and head removed to reseal the pushrod tube. I imagine that the manifold would stay with the head in this operation.
 

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Hi Jim,
I'm pretty sure he took the carburetors off to remove the head. Then again I have a T140V engine in my 70 Bonneville and I can't imagine getting the head and push rod tubes back on properly with the carburetors mounted.
 

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I imagine that the manifold would stay with the head in this operation.
Hi,
I was not thinking of the manifold to carb seal, but the carb to manifold seal this would have definitely been dismantled to remove the head. When the carb is refitted there should be a small gap left between the carb flange and the manifold, where the carb sits on the O ring. The carb and manifold flanges should not be touching.

If there is no permanent distortion, just slackening the mounting nut 1/2" a turn might improve your situation, it is an easy 5 minute thing to try. This is a common problem encountered when the carburettor has been refitted.

If it does not improve, then you will need to dig deeper, and spend some hours dismantling your bike to find another cause for your throttle sticking.

Regards
Peg.
 

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Most times, the carbs would have been removed before the head came off. The carbs would get in the way when refitting and looking to see the rear pushrod tube was entering properly. I find it a bit unwieldy to leave carbs on the head when doing this work. Just unbolt and hold them out of the way with cables still attached. Most likely the carb is now a little warped.
 

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Since you paid a specialist for work on the bike and the fault has only occurred since he did the work, perhaps he should be the man putting it right?

Rod
 

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Discussion Starter #12
Just getting back to say, the 1/2 turn remedy worked like a charm. No more sticky throttle. Thanks again, Jim
 
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