I have a stage 3 Predator 212cc Billet rod and flywheel with 22mm Mukuni and a couple weeks ago my wife's nephew wheelied it over. I believe that the stock Rupp jackshaft sprocket is a 10 tooth 41 pitch. Would installing a bigger 12T or 14T jackshaft sprocket soften the acceleration off the start? Being that the original engine is a Tecumseh HS40 which the gearing was originally set for. My built-up Predator 212cc is about 3 times more powerful than a stock HS40. Despite telling people to take of easy and not to twist the throttle too much it is apparently un-ridable by novices as seen in an earlier posting of the damages. Plus as an added benefit would this increase top speed a bit. Although it is plenty fast over 50mph right now.
Larger more tooth replacement jackshaft sprocket for a 1971 Rupp Roadster 2
- Thread starter GustoGuy
- Start date
I see that Blackwidowmotersports.net has an 11 tooth jackshaft sprocket originally for the 10 inch wheel bikes that can be used on the 12 inch wheel bikes for higher top speed. Would the additional tooth help to soften the acceleration. I also have a heavy Suzuki K10 Motorcycle fork on it too that is over twice as heavy as the Rupp springer front fork.
I agree. A built gx200 or Predator 212cc is way more powerful than a stock Tecumseh HS40. I remember reading about a member here who has a built Tecumseh HS40 and he said it can run with a stock Honda clone. Mine is built hits too hard off the bottom. My wife who has ridden my Resto-mod Rupp says it scares her a bit so she takes it real easy. She had driven Motorcycles before and the only reason I let my 34 year old nephew ride it is because he said he rode a 125cc Yamaha dirt bike during his teenage years.
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All good questions...
https://www.eccarburetors.com/jackshaft-calculator.html
https://www.eccarburetors.com/jackshaft-calculator.html
I did a quick calculation and the difference is about 1.101 or approximately 6 mph faster. I should definitely get the 11 tooth jackshaft sprocket since it should hopefully tame the bike wanting to jump out from underneath you a bit better than the stock 10 tooth jackshaft sprocket. I even think that it hits too hard off the bottom and i used to ride a 1992 CR250 dirt bike that my brother owned. Body english is definitely required to ride my bike and you have to lean foward if your going to try and gun it. When talking to him after the accident he said that he was grinning from ear to ear while riding it and when his cousin took off on the Predator powered Doodle beast he said that he only wanted to out accelerate the other bike and he said he was sitting back on the seat and was shocked by how the bike front end came up. I want no more accidents. Plus I am banning most riders now.
I am going to buy the 11 tooth jackshaft sprocket since this should dampen the tendency a bit towards trying to pick up the front wheel. My wife is right. She says people at car shows don't let people drive their cars so Superman wannabes will not be flying off my bike since they obviously can't listen to me when I tell them take off easy and don't crack the throttle. Easiest solution is "Bann them all" because they will probably eat $hit if I let them drive it. A position sensing switch which cuts the ignition if tilted could work. It would have to be set for at least 10 degrees of tilt before it cuts the ignition so it will not go off if riding up hills or descending hills. Could work. I removed the original anti tilt mechanism and inserted a bolt in the Predator 212cc engine block. Mount it on the frame right infront of where the ingition wires switch is. However if someone pegs the throttle it may still come up despite the ignition cut off.
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I ordered the 11 tooth jackshaft sprocket to replace my factory 10 tooth. Hopefully this will slightly soften the acceleration off the start. Spin the throttle on the bike right now and it will jump out from under you. Hopefully the 11 tooth sprocket will make it less likely to inadvertently wheelie over. Plus no more newbie riders.
Thanks, I'll look at that fork. Yes I'm worried about the rupp with a 196. I'm too old for wheelies! Btw I'm already extending the rear wheel back about 4" inches for just this reason. I attached a pic of the mock-up. My plan B is to swap out the built 200 with a stock gx160... And there's also the question of how the rider's gonna sit - probably leaning slightly forward...
