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Discussion Starter · #1 ·
Hello

I have a 1979 honda cg125. It is running rough and backfiring through the tailpipe. Ive read alot of things about the difference between backfiring from running rich and running lean, and i think it may be running rich and i need to clean the carb and check the jets and float.

Here are some symptoms

1) when i downshift to engine brake it will backfire.

2) this makes me think its the timing, i am unable to get it past a sort of ceiling of RPMs. when in gear or in neutral i throttle wide open, it revs up and then plateaus and kind of stutters, feeling like its not quite at full power.

I guess this could also be that a too rich mixture is giving incorrect combustion? or that the timing could be bad?

3) it sometimes runs rough or misses when accelerating.

any ideas advice, or order to treat things?

thanks so much
 

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American Legion Rider
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26,368 Posts
One thing to check and one to try first before tearing into the carb.

Check the air filter or possible just change it.

Try putting can Sea Foam or bottle of Chevron Star Tron in the fuel per the directions. You'll need to run a full tank though to possibly see any change. But if You have enough throttle to do that safely then it might clean the jets up some to postpone a complete tear down of the carb. This assumes you've not done anything that may have caused this to start with.

Worth a try.
 

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Your symptoms seem to be more carburetion than ignition, to me, but, it shouldn't be hard to check the timing.

From what I found, Honda went to a CDI on that model; over time, the electronics can fail because of the high Voltage on the capacitor and controlling transistor/SCR, so intermittent spark is a possibility. Running it with a timing light should show spark jumping around, if that is the case.
 

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Discussion Starter · #6 ·
Hello everyone, thanks so much for your replies

I live in Switzerland, so we dont have Seam Foam or Chevron Tron.


the air filter still has its two foam rings around it; i guess i can try soaking it in some solvent to see how dirty it is?

i pulled the plug and it was quite black

according to the haynes it could be an oer rich air fuel mixture, faulty choke or blocked air.

i will try to replace the plug and clean the filter and see if that clears things up

thanks so much for everyones help, i really appreciate the not so "trolly" answers here. i have two CG125 and i really like them, but also getting a headache of these types of problems.
 

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