Author Topic: Cause of pops & bangs from the exhuast at / or close to idle speed?  (Read 673 times)

Offline McCabe-Thiele (Ted)

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When I did my dynamic timing a few days ago I did it for 1/4 initially so today I spent over an hour trying to get the timing marks for 2/3 spot on at the same time.
A long winded process as one of the modules was close to it's limit on the clamp screws so undeterred persevered by way of moving the 1/4 module on the back plate then re-timing to 1/4 then again for 2/3 - repeat until you start to forget when it's too advanced / too retarded.

Conscious of not spending too much time with the engine running & not cooling with movement  I made most of the adjustments on a stop start basis. I have it pretty darn close for today - I will check it again tomorrow when I can stand up straight again. It was towards the end of the process that I sat in a chair with the bike lift raised to it's highest position.

It's not an issue when you rev the engine but at idle speed there does seem to be quite a bit more backfiring from the exhuast system than I would like- it's a Motad system what is the most likely cause please?
My carbs have not flooded with no petrol smell evident - engine idles at 1200 rpm whilst checking the timing in the F position.
Honda CB500 K1 (new pit dug out ready)
Honda CB400 four super sport (first money pit)
Link to my full restoration http://www.sohc.co.uk/index.php/topic,23291.0.html

Offline Johnwebley

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Re: Cause of pops & bangs from the exhuast at / or close to idle speed?
« Reply #1 on: April 30, 2022, 03:33:15 PM »
Popping in the exhaust could be caused by air leaks were they fit in the head.

Try putting your hand over the end and see if you can hear any hissing.



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lifelong motorcycle rider,and fan

Offline McCabe-Thiele (Ted)

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Re: Cause of pops & bangs from the exhuast at / or close to idle speed?
« Reply #2 on: April 30, 2022, 04:07:58 PM »
Popping in the exhaust could be caused by air leaks were they fit in the head.

Try putting your hand over the end and see if you can hear any hissing.



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Presumably you mean when the engine is not running!
I'll try turning it over with the kickstart & might use a listening tube if it's not obvious.

I know the exhaust was leaking before the rebuild from number one cylinder from the soot deposits and the uneven squash on the old gasket. It was difficult to get the four pipes into the silencer box with any dignity.
« Last Edit: April 30, 2022, 04:24:29 PM by McCabe-Thiele (Ted) »
Honda CB500 K1 (new pit dug out ready)
Honda CB400 four super sport (first money pit)
Link to my full restoration http://www.sohc.co.uk/index.php/topic,23291.0.html

 

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