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Discussion Starter · #1 ·
So, I have been upgrading my tired old '71 CL175. Replaced the coil, wiring harness, charlie's place ignition, got my stator rewound, li-ion reg/rect and battery, new plugs

The bike fires up fine and rides for about 10 minutes then starts backfiring, stuttering, sounds like its running on one cylinder. What else could it be? Seems electrical
 

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Pop the tank cap and listen for a hiss, tank vent could be plugged and you're running out of fuel at the carbs.
 

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Discussion Starter · #4 ·
Plugs look pretty good
I just flushed and redkoted the tank, rebuilt the petcock and new fuel lines and filters. I removed the carbs and will be rebuilding them tomorrow just in case it is a fuel flow issue
 

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Stop throwing parts at it, it will just leave you broke and frustrated. You should have left it together for troubleshooting since you still do not know if it is fuel or ignition.

Run it until it quits, remove the float bowl drain and see if fuel comes out. You could also put an inline clear filter in the fuel line and see if it runs dry. Starting fluid can also help troubleshoot as to whether it is ignition or fuel. If it fires off with starting fluid it is a fuel problem.
 
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It sounds like a vacuum leak to me. The engine gets hot, then the rubber boots between the head and carbs gets hot, they expand allowing small cracks to become vacuum leaks.
TOOLS
 

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The part about "rides for 10 minutes" makes me think it isn't getting up to normal operating temp so maybe not a heat related problem.
 

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I thought it might be leaning out too, which is why I asked about the plugs, but may also be a fuel delivery issue or something else! It's just a matter of eliminating one at a time. Fuel is easy to check, with the clear lines as mentioned above.
 
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