motor dies on extended uphills.

fponias

New Member
Jul 8, 2019
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Setup: Trek 960 with stock ebay "80cc" conversion kit. NT carb and generic gas tank. I have to idea how to verify the actual engine size so I'm assuming it's a 40cc. The rear sprocket has been upsized to a 54T. I upgraded the tensioner to be spring loaded but it has still been giving me issues.

So I'm mostly riding offroads around my house. That means I put a 54T gear on the rear and have to tighten the spokes every 2 miles. I'm switching to a jackshaft build because even the relatively "low" torque for a 5.4:1 gear ratio is shredding my spokes Most of the riding I'm doing is really hilly terrain; extended uphills where I'm pedal assisting to keep the motor running and lengthy downhills where the motor isn't even engaged.

It runs fairly well. The problem is: after few minutes on extended uphill sections the motor will start running slower and slower until it finally stops altogether. It usually starts doing this after about 3 minutes of continuous use with wide open throttle, low rpms, and occasional pedal assists. My method of dealing with the stall is to wait a minute to let the motor cool, turn the bike around so it's pointing downhill, and bump start the engine back to life. Then it's another few minutes of uphill and it dies again. The other symptom I've noticed is fuel is seeping around the bottom of the air filter. There's not a lot of fuel, just a small leak. The air filter sponge is not completely soaked with gas or the motor probably wouldn't run.

I'm assuming it's carb. The most obvious answer is it's not designed to be tipped back even 20 degrees for an extended time and that I need to upgrade my carb or rotate my engine forward. Since it's a new carb, and it runs smoothly on the flats and downhill, there's nothing wrong with it right?