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a 'pop' and misfire

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Entertwainer
Trackday Trickster



Joined: 13 May 2013
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PostPosted: 20:21 - 02 Jun 2014    Post subject: a 'pop' and misfire Reply with quote
twice today this has happened.
both times while accelarating - and a good amount into my commute (so engine nicely warmed up).
give a little throttle to pull away and a misfire and a 'pop'.

is this a dirty carb thing? whats the pop all about?
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Honda CG 125 W - Turkish - 1998 - 2015 RIP
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Lord Percy
World Chat Champion



Joined: 03 Aug 2012
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PostPosted: 20:47 - 02 Jun 2014    Post subject: Re: a 'pop' and misfire Reply with quote
Entertwainer wrote:
twice today this has happened.
both times while accelarating - and a good amount into my commute (so engine nicely warmed up).
give a little throttle to pull away and a misfire and a 'pop'.

is this a dirty carb thing? whats the pop all about?


Firstly, check that your choke is switched off. If it's an autochoke, check it isn't malfunctioning in some way. If that's all ok, read on.

It could mean your fuel mix is too rich. The misfire would be caused by there being too much fuel with too little oxygen. You would fix it by very gently turning the idle screw on your carburettor by a fraction of a turn (maybe 1/4 of a turn), anticlockwise. This allows a tiny amount more air into the carburettor while the bike is idling, so the fuel-air mix should be at the right level again, hence no problems with it igniting as you pull away.

If you aren't sure where the idle screw is, just google "<your bike model> carburettor" and look for some labelled schematic images.

If the idle screw doesn't fix the problem, remember to turn it back to where it was originally.

The 'pop' sound is presumably a backfire from the exhaust. This would be caused by the excess fuel (which didn't ignite because of the mixture problem) making it straight through the engine to the exhaust, and gathering until it gets a chance to ignite, hence the pop.

Disclaimer: Someone may come along to completely falsify everything I've said. That's all the stuff I'd consider first though.
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gavbriggs
Crazy Courier



Joined: 11 Jun 2013
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PostPosted: 22:03 - 02 Jun 2014    Post subject: Reply with quote
To alter the air/fuel mix you will need to locate the mixture screw. The idle screw will simply alter the engine rpm at idle.

If you alter the mixture you will hear the rpm change, select a high rpm then turn the rpm down via the idle screw, repeat with the mixture screw until you find the sweet spot. It's not exact but should get you n the right ball park.

I would however check the ignition circuit soundness first just to make sure there's no spark plug damage or leads damage. Also check there's no leaks on the carb/air filter box etc and as said that the choke isn't stuck on.

Look first for defects before changing previously correct settings.
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Recent bikes: Varadero 125 - Mod 2 3/2/14 - Bandit 1200 SK4
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Lord Percy
World Chat Champion



Joined: 03 Aug 2012
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PostPosted: 00:00 - 03 Jun 2014    Post subject: Reply with quote
gavbriggs wrote:
The idle screw will simply alter the engine rpm at idle.


Ah yeah that's right. My bad. I was thinking his problems were when pulling off from stationary.
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Entertwainer
Trackday Trickster



Joined: 13 May 2013
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PostPosted: 13:14 - 03 Jun 2014    Post subject: Reply with quote
ok, thanks. it didnt happen today, ran fine all the way in.
the choke was off for both incidents.

will take a look at the plug/leads etc before making any changes to fuel mixtures.

thanks for the help guys. hopefully it was a one off.....
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Lord Percy
World Chat Champion



Joined: 03 Aug 2012
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PostPosted: 14:02 - 03 Jun 2014    Post subject: Reply with quote
Entertwainer wrote:
ok, thanks. it didnt happen today, ran fine all the way in.


Good stuff Thumbs Up . Maybe it was just a dodgy bit of fuel.
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