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Old 06-23-2011, 12:25 AM
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scotto- scotto- is offline
Custom 4-Stroke Bike Builder
Join Date: Jun 2010
Location: Ridin' inSane Diego, CA.
Posts: 6,504
Wink Re: Custom Frame For Thumper Motor

Originally Posted by culvercityclassic View Post
I am posting an update on this bike from past events. The bike is now complete and running. It runs very strong and very quick off the line. I built this bike to race at Willow Springs and did just that. It performed very well but not as well as the built AGK bike that raced in the unlimited class, that bike was sick fast with a top notch rider on it.

I noticed a few issues that I have since corrected; the first was oil blow by out the vent in the valve cover. I added a hose from that area to the air filter, the air filter became saturated with oil and basically sprayed down the side of the bike, back wheel and ground. It was a complete mess and a safety hazard. I searched for an oil catch can for these issues and could not find one to my taste so I designed and made my own; Inlet on side, vent on top, oil sight tube on side and a drain on the bottom. Installed it today, sure works nice…problem solved.

The next issue was the CVT was not geared right, it was quick but wanted to climb the drive pulleys too fast, I was given a 50 tooth sprocket adapter at the race as a prize (Manic Mechanic thank you) that I installed to correct the problem. This helped and the bike will pull the front wheel off the ground from a dead stop and lug along at 45MPH all day. This might be the setup but will need to ride it more to find out. 45 is fast on a bike that has no suspension with only a spring seat.

On a side note: The motor had no problem with over-heating and I ran the crap out of it all day at the race…still impressed with this motor….

Bye Bye China Girl…hello THUMPER…
Great to hear you ironed out a few small details Jeff....can't wait to take er for a ride again Looks like oil changes are a breeze with that angle the engine sits and I see you swiss cheesed the rear sprocket already......nice. That stainless 52t I got is gonna damage drill bits to lighten up

Looks like I'll be building a race specific bike next for these go-kart tracks we be racin on......seeing as how my 49cc bike is way undersized and under-powered compared to what they're letting race in the 4-stroke class.....the wheels are turnin!

Love your bike man, it rides like a champion! So do you!

EZ Motorbike Dealer - San Diego, CA.
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