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Old 05-29-2011, 01:04 PM
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agk agk is offline
Motorized Bicycle Elite Member
Join Date: Oct 2010
Location: Santa Barbara CA
Posts: 151
Default Re: Custom Frame For Thumper Motor

That brace you made coming off the cylinder head looks like it will do a good job supporting the engine. The header you made looks really nice too. It's going to be loud!

I would suggest using the stock plastic fan on that non-finned REV flywheel. The non-finned flywheels work great for a few 1/8th mile or 1/4 mile blasts. I don't have any experience using a non-finned flywheel for several laps on a road course in 90 degree weather. I would at least use the fan while you get the carb jetting dialed in and determine the proper oil level for this arrangement. Then you could get a baseline engine temp with the fan before running the motor without. I realize the race is right around the corner and you will not have much time for experimenting with and without the fan.

My go kart motor will get hot on warm days running on our dirt oval track. I have the fan, cooling tins and blower housing in place. When the cylinder head temp reaches about 440 degrees I will let off the throttle and cruise around the track for a few laps while the engine cools down. It seems all the cooling parts do their job at lower speeds and the air passing over the fins on the cylinder head at high speed is not sufficient to cool the motor.

My go kart motor is a 6.5hp Harbor Freight engine. It may not, however, be a good comparison as my motor uses high compression and some other mods that may contribute to running hot on warm days at the track. I just want to share my experience with you as it may help you with your engine mods.
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