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Discussion Starter · #1 ·
I just purchased an 1979 Suzuki Gs425. I have noticed a few issues so far. The bike runs, drives, and shifts but, I am getting this puffing noise out of the carburetors during idle and low gear. The puffs actually rattle the pod filters. I’m not sure what is causing this? Possible over fuel? Fuel mixture off? Vacuum leak?

That leads me to the next point. The bike has pod filters and straight pipes. I was told that the carbs were re-jetted to compensate for these mods. I have also found an exhaust leak on the left exhaust pipe.

I took the spark plugs out of the bike and they are black at the tips, carbon build up. I’m not sure if this is caused by the exhaust leak or fuel/air mixture incorrect or both. I did notice that the exhaust smells very strong! Possibly gassy.

In conclusion I am having some issues with puffing of the carburetors, black spark plug tips and very strong exhaust odor (gassy).

Thoughts:

Could these issue be from improper timing, fuel/air mixture, or exhaust leak?


Thanks!
 

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Discussion Starter · #3 ·
Thanks! Yeah, I thought I was running rich. I have been riding the bike and noticing a lot of back firing happening out of the pipes when I turn the bike off and when I’m in low gear the carbs puff. Would i have to change main jets to fix rich issue?
 

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So, are you saying there was zero change after correcting the exhaust leak? You need to run it hard and get another reading on the plugs. If you've done that and still running rich, then yep, time to re-jet. I have no idea what it might need to be but I'd drop down half way between stock and what you have for starts. Except for the hassle of doing it, jets are not that expensive. But maybe someone knows exactly what size you need too so stay tuned.
 

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I just purchased an 1979 Suzuki Gs425. I have noticed a few issues so far. The bike runs, drives, and shifts but, I am getting this puffing noise out of the carburetors during idle and low gear. The puffs actually rattle the pod filters. I’m not sure what is causing this? Possible over fuel? Fuel mixture off? Vacuum leak?
No no no! Spitting out of the carburetors is a lean condition probably caused by improper jetting with open pipes and probably cheap pods. You are most likely going to damage the motor if you continue running it like that. You might also have a valve adjustment problem or bad carburetor boots or O-rings. I know black plugs indicate a rich condition so you probably have several things going on that need correction. Just running too rich would eventually fowl the plugs and stop firing.
 
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