Topic: Click in exhaust note - Solved?

[jmckinne]

I've got a little noise in my exhaust note that is driving me nuts....

74 750K,
Carbs freshly rebuilt.
Exhaust replaced (tho not diffusers).
Timing set dynamically.
Valves set - I think. The clearences are SO tight.
Carbs Sync - I think. My motion pro is fussy.

I get a little clicking sound at the tailpipe on either #3 or #4, hard for me to tell which. I don't hear anything up at the head, only at the tailpipe. The engine's smoothness is definately affected when it happens tho.

The clicks are not regularly spaced, and are barely audible.

The frequency of the clicks is effected by changing carb settings and/or synch but I have no idea how so I can't adjust it out. Wehter the carbs are the cause or messing with them just has an effect on the click I can't say.

Anyone got any ideas for me?

thx in advance.

[jmckinne]

Well I didn't get any responses to this so that must mean it's a hell of a tricky problem right?, lol. I've done some more work on the problem, and have in fact eliminated the sound so if you were watching this thread for answers to the same problem on your bike here goes...

First of all "click" may not be the right word for it. It sounds like a click but not a very mechanical or mettalic one. It is very hard to describe. It is accompanied by a very noticable puff at the tail pipe of the cylinder that is making the noise. Something didn't fire right, that you can tell. If you have this sound I think you'll know what I mean.

Anyway, on my bike it is VERY DEFINATELY RELATED to carb balance. Whether this is the cuase of the problem I can't say for sure, but by adjusting it you can make the noise go away - on my bike.

I went to do a carb sync on the bike again. This is always frustrating for me because I have a MotionPro and I've tried a variety of fluids in it but none seems ideal. It either pulls to easy or gets bubbles in it or both. Mercury is the way to go here, but they don't sell them that way anymore - sigh. If anyone knows where I can buy mercury and if that will work ok in a MotionPro designed for "manometer fluid" let me know. Manometer fluid sures looks like blue glycol to me, but I digress.

I did my sync as usual and got what appeared to be a good mach on all four. But the click was real bad. It's always been #4 before and I assumes it was again. I walked around the bike and... nope 4 was fine. Cylinder one was clicking away nicely tho. I played with #1's balance adjustment, going each way by small amounts. Going one way the click disappeared. At this point my #1 setting looked a smidge lower than the others but the bike was idling great. Here's what I think I learned, some expert tell me if I'm wrong - or right.

1) Carb sync on a SOHC is far more touchy than on some other bikes. Slight variations can have a big effect.
2) Even if your Sync'er is perfectly setup with a pre-balance adjustment etc, in the end a straight line across may NOT be the best thing for your bike. Your sync setup could still have some variation so be prepared to get it close with the sync'er and then make some very fine adjustments by ear. If the bike runs better, you done good.

I'm especially curious if #2 is something that experts do as well, or do they just go for a straight line across all 4...