Loose butterfly shaft - bearing surface worn???

So. I bought my second 750 Seca this spring (after my first one was destroyed in a fire over the winter ::weeps: , and have been chasing various gremlins on it...

So far, have corrected a couple electrical gremlins, readjusted everything, done rear brakes, lubed everything, checked compression, valves (all within spec), and rebuilt the carbs (without pulling them apart and doing shaft seals).

Once I got it all back together, mostly bike was happy, but had a couple little gremlins left, including a 5krpm hanging idle, and a RATTLE from the #4 Carb at idle. Vacuum leak, anyone?

I did the propane test, and outer seal on #4 went VROOOOOOM. All others were OK. And then I looked closer. The whole bloody shaft is vibrating fore and aft with vacuum pull, which is probably not only sucking air through the seal, but also making the #4 butterfly let air through intermittently, which would explain the crazy behavior.

The shaft seals (u-shaped rubber) are soft and pliable and seem perfectly happy, so I fear that either the shafts or the bearing surfaces are worn. Anyone else had this problem? Is there a rescue other than replacing the entire carb? How screwed am I?

 

How can you tell that the throttle shaft seals are "happy" when you can't access fully half of them without pulling the butterflies and shaft seals? One on each carb is trapped by the shaft/linkage.

In the case of this particular carb, the shaft and or carb body could very well be worn but it would have to be fully disassembled to determine exactly what is worn out. You also may be seeing the "normal" amount of play between the shaft and carb body but that seal is completely gone so the shaft isn't being held "centered."

 

Hi BigFitz; thank you for your post.

I mis-wrote; the only seal I checked was the outside seal on #4, where the play is, and where there seems to be leakage and weird behavior. That seal was firm rubber, U-profile with the opening to the outside, edges clean, pliable, and seemed to fit quite well in principle. If it's only the seal that's shot, I'll just about eat my hat...

unless P.O. did a carb job and used the WRONG SEALS? Possible???

No other spot on the carb failed the propane / carb cleaner spray test, from which I am inferring (perhaps overly optimistically) that the other seals are still in order. Ah well. Suppose I'll be putting an order in to Chacal (or going hunting here in Euroland - Swiss customs can be a pain in the tail.) Perhaps b

Wish me luck!