classic motorcycle forum
Motorcycle Discussions => British Bikes => Topic started by: 70Bonnie on August 14, 2011, 11:41:37 PM
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Been lurking around for a while and now I need an opinion so I signed up. :-) 1970 Bonneville, no balance pipe, Dunstall megaphone copies, no baffles. Head has been decked and I am using a thicker head gasket. (.080" copper) Plug looks good, nice tan colour. The right side exhaust has a chirping/whistling sound as it winds down after throttle. Left side is fine. I wear earplugs so I hadn't noticed it. A buddy riding behind me heard it and let me know. I checked the tappet clearance in the right exhaust and it was tight. Reset to recommended .004 and no change. There is no noticeable loss in power/compression. No strange sound when listening to the engine, it's only noticeable at the muffler. All opinions appreciated.
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Are your exhausts and mufflers identical side to side ?
Can you swap the Dunstalls side to side, see if it changes side ?
A lot of exhausts chirp/whistle on the overrun - Norton Commandos had those famous 'tweety' mufflers, aka as peashooters.
Although not sure that Dunstalls would fall into that category.
Not something partly blocking one inside anywhere, is there ?
Is is pulling strongly on both cylinders, carbs synchronised, one cylinder is not doing more of the work ? Will it idle on one cylinder, each cylinder in turn ? (don't do this if you have electronic ignition).
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It's a stumper. Same pipes and mufflers. Even swapped in a pair of real Dunstalls off my '72, no change. The chirpy side doesn't idle quite as well as the other. I did a check by squirting carb cleaner through and it doesn't look blocked. It pulls well when the throttle is opened, carbs are synched. I haven't swapped out the pipe though. Could unscrew the exhaust pipe adapter and swap a push-in just to test and see if that solves it. Then, as you suggested, I'll know if it something in the pipe is causing it. Old school....I like my points. LOL
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I would whip the head off and have a peek my VB had that noise and it turned out to be head gasket failure.
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Headgasket noise is most noticeable when under power not over run.
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Head gasket is new, I put it on. No Oil leaks at the gasket. Couldn't get a fit with the push in pipe so I abandoned that idea. I ran it a bit with no pipe and couldn't notice any mechanical noise. I have to go back to it being some irregularity in the pipe. Sound plausible?
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Does to me.
Just one of those idiosyncrasies of old bikes, allied to the weird effects of harmonics, etc.
Goldie owners used to make a big thing about the over-run twitter, as do Beetle owners... ;)