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Old 06-11-2016, 09:04 PM
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Agreen Agreen is offline
Motorized Bicycle Elite Member
Join Date: Feb 2013
Location: Goose Creek, SC
Posts: 632
Default Re: Help a Veteran with New engine crackiling and 4-stroking

This is easily fixed. Your main jet is too large. Solder and drill it smaller, or buy a $15 kit of jets. I prefer soldering and drilling. One drill kit will cover every carb, every jet, and can do the same size multiple times. A jet kit can only be used for one type of carb, and if you use one size, it can't be used on another engine.

Anyway, thin out the main jet, but understand that you might need to readjust the needle once it's rejetted. The needle effectively modifies the size of the main jet, making it smaller for when you're at partial throttle. So with a smaller jet, you may need to go down on the clip (this raising the height of the needle) to compensate.

Don't do any porting until you have read Gordon Jennings book about 2 stroke tuning. If you cut the skirt of the piston to where you can't see any of it at tdc, you will actually lose power. I did it, and immediately regretted it. The engine is port timed, so if you change the height of the port, you change the opening and closing times. Bad things can happen if you don't know exactly what to do.
Never stop wrenching
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