Gearbox binding?



I got a new 50cc 4 stroke from Spooky Tooth Cycles. (Desert Rat)
It's a fun bike. When I let off the throttle it jerks quite a bit. It feels like the gear box is binding up. It ramps up to 20mph smoothly, the chain and sprockets are in line. I filled the gear box half way with 80 wt gear oil per their instructions, but I have gear oil seaping out after I run for about 5 minutes. I read some other posts and read a comment on lightly greasing the gears vs. gear oil. If any of you more experienced guys could lend me some advice, I'd greatly appreciate it.

I also am looking for her to go about 30mph. Right now she'll only go 20. I'm 6'1" and 190lbs. Can I modify the exhaust, larger sprocket, ect or am I just (blowing smoke) if I want to get her to do 30mph with only a 50cc motor.



"Crunchy" Gear box

Hi I have a similar engine and gearbox. I have found the 10 tooth sprocket on the rear of the gearbox, the one that actually drives the chain, is burred, and designed incorrectly. I spent about 3 hours with a dremel with a diamond drum on it, working down the sprocket till the chain would go around it. I did not use the kit chain, I'm using a much higher grade chain, a KMC 415. I put Hypoid in mine, and it was a bad deal in a way, as there was some solid grease in it first, and the Hypoid went down there and whipped it to a fluff, and it "Erupts" continiously from the vent hole in the fill-plug bolt.
Power, well mine accellerates well, I was really babying it for the fist bit, as the sprocket was real choppy. Now that I've got about 10 miles on it, the sprocket is smoothing it's self out, and there's been an initial streaching and seating of the used rear sprocket, new chain, and reshaped front it is ready to re-adjust the rear wheel.
I have yet to install my front brakes (this fork won't handle it) nor have I installed a speedo(I'll use the lil Whizzer speedo, a very nice Stewart Warner unit). I've built and ridden many of these lil Motor Bicycles and I would guess, from feel, that mine accellerates well and I would say gets to 20-25 very easily, I weigh about 275, and I installed a wheel I had previously used that has a 44 rear. I think the bike, on a longer straight, say 1/4 mile, should hit 35 with no trouble.
It's been reccomended to me, to use some 90wt and some "Lucas" oil, this is a viscosity improver (like STP). It would seem that 4-8oz of grease would be plenty, as we do not want it splasing all over the place?
I'm going to pull the cover from mine, clean it all out, and begine to experiment with different gearbox lubes.



found the problem

My centrifugal clutch isn't disengaging when the motor gets down to idle. Took the cover off of my gear box and the clutch housing is blued from the high temps and my gear lube was cooked to a nice black color.

I'm gonna chalk this up to one of those now I know what to look for if it happens again lessons. I gotta feeling I'm gonna be learning alot of those over the course of the next few months. but I gotta tell ya I am sooo sold on these bikes as a way to commute safely, help lessen the impact of my 18mpg mini-van not polluting air, and it cheap if your strapped for cash. does anyone know if a replacement gearbox is available anywhere on the net or if it's possible to modify someone elses?

Mine was a wet clutch - I looked a dry go-cart clutches that accept a 10 -16 tooth gear I could just put directly onto the drive shaft. Would it hurt my engine which is still good if the new clutch wasn't sealed around where the drive shaft comes out of the motor? I also would need to figure out how to get it to align with the rear drive sprocket... thought maybe have a new enging mounting plate fabricated in town for cheap and just sliding over the motor 2 inches. It would mean my cranks would then hit the new engine mount and would need to be widened out if such a thing is possible or id be limited to just to motor power and couldn'e ever pedel if I had too which would suck until i could figure out a better design or gearing setup.
The guy I bought the bike from is sending out a new 2 stroke motor/gearbox next week to replace mine with the factory defect. I have no problem mailing him a couple hundred bucks back and keeping it as a backup cause I really want to keep my four stroke on there if I can. I've gotta drive 21 miles each way to work and have got the 4 stroke broken in now. I've heard - and maybe you guys who have a lot of miles under your belt would know - but will the 80cc two strokes hold up for long huals every day in the heat of summer as well as a 4stroke? The owner at Spooky I've spoken to on the phone knows these motors well and I trust him, but is a 4 stroke better suited for high mileage or is that just an old wives tale?
I'm also working out the final ideas for my second bike and the extra motor would be nice to all ready have.

I've read about some of you making your own gaskets - one guy said he made his from cardboard - where do you get real gasket material to trace out a pattern? This is a great idea and will save a few bucks.

Thanks ahead of time for helping out the new kid on the block.


Active Member
Dec 15, 2006
you can get gasket material at any auto supply place
go with high temp material and you should be good
way cheaper that way too !!!


good humor

like the pics of your girls ~ i've got 2 boys and 2 girls 11-9-7-3
i'd post a picture but i cant seem to get them to stand still long enuf to take one lol