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Author Topic: Need to rejet carbs for megaphone style exhaust?  (Read 2714 times)

Offline Winterfield

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Need to rejet carbs for megaphone style exhaust?
« on: May 27, 2020, 09:36:43 AM »
Hi all,

Due to budget constraints I've opted to get a cheap megaphone silencer from Classic Bike Shop (https://www.classicbikeshop.co.uk/short-universal-megaphone-silencer.html).

Will this be likely to change the back pressure enough to warrant re-jetting the carbs? I'd prefer not to, with the intention of buying a replica 400 silencer when (if?) they become available again. Would adding a baffle change the back pressure?
 
Cheers.
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Offline Johnwebley

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Re: Need to rejet carbs for megaphone style exhaust?
« Reply #1 on: May 27, 2020, 10:34:52 AM »
Possibly.

Try it

Do a couple of plug chops.
To check

Sent from my SM-A750FN using Tapatalk

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lifelong motorcycle rider,and fan

Offline K2-K6

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Re: Need to rejet carbs for megaphone style exhaust?
« Reply #2 on: May 27, 2020, 07:24:05 PM »
As John says, you'd only see by trial and error.

If there's any evidence of it running lean at first appraisal,  lift the needle jets by one notch (circlips lower) and use higher numbered spark plugs from NGK 8 to a 9 to give some margin for error.
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