71 Rupp Spitfire

Mini Bike & Go-Kart Parts

#1
Hi folks,
Been on the site for a bit, decided I’d share my bike.
Started life as a 71 Rupp frame, forks and swing arm. Dubbed the “Spitfire” because it would backfire pretty good with the first muffler so from there the name stuck.

We do a lot of ice racing in the winter so I needed something to compete with the other rupps on the pond.

Ended up painting it with some Dodge Viper red that I had leftover from a car project, I printed up some custom Rupp decals with my own twist on them. Had to make a few modifications to make the Hm100, what I called the “Dwarf Star” to fit. The spark plug is very close to the frame so changing it requires pulling the tank. Started with a Points Ignition Hm100 which was the 333cc block with star rod, 425 lift cam. Fueled with a D-slide carb. Stock exhaust that was hogged out. it runs a Tav20 torque converter, comet belt with no problems at all. Additionally I was able to find an electronic ignition box that utilized the points coil without the condenser and points which allowed for higher RPM and easier pull starting with the 425 lift cam.


After a bunch of racing the old hm100 It developed a ton of blow by and lost compression. I was able to buy a new star block, cam, rod and piston for under $150 Locally. I did have to install a decompression with the star cam Which I like more than the 425 cam so there was some head machining to make that work properly on a pull start bike.

From there I made some steel extensions Out back to make the bike a little longer. Machined an adapter for Some hydraulic front forks. Some Yamaha rear shocks.

There’s so much I’m forgetting at this point, but I’d like to keep this post updated as I modify the bike more.

Mock up before paint
19249A10-9B0B-48C2-B458-753AD95B32CB.jpeg Finishing up the initial Assembly FEB853A4-4DBA-4CA2-9FDE-06029BD6BDF2.jpeg How it looks today with the star. F9782E04-125E-411E-B7E3-11D7583F1453.jpeg
the bike at this point has some mild modifications, larger exhaust piping, RLV muffler, billet tappet cover. Some other small goodies.
It’s a handful but it’s a blast to ride
 
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#5
B0B408EE-6E2F-40AB-86F9-F5657F0930FB.jpeg
Also got the 420 chain on, aluminum throttle tube and bar ends in, just looking for a cast aluminum pull start assembly at this point, maybe some more tweaking on the forks.
 
#6
Haven’t posted much. Couple weekends ago took out the bikes to do some ice racing. Here’s a photo of my bikes with my old mans star powered Rupp as well. Always a good time, was a good test and tune day to shake out the bikes. We had I believe 11 minis out that day. Hopefully be getting back out in the coming weeks if the cold weather hangs around!
 

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kayde

Active Member
#11
The bigger 12" wheels look so much better.

That recoil is way cooler too.

Thats a beast of a bike hopefully it dont live up to it's new name.
 
#13
That thing is insane!, the first thing that came to mind was a 350 small block in a Chevettte. When you say "Chrome the blower housing", you mean a Roots blower... right?, Hahahaha.

1619232634466.png
 
#18
Won the hill climb drags and the circle track races over the weekend! Bike absolutely rips, I can’t keep the front end down. Got some killer trophies too. 31601F64-71EF-4744-9A4D-77F186C85A82.jpeg
Decided to pull the engine out, going to put a Star crank in it out of one of my spare stars and freshen it up with a hone and some rings. I should have it back together within a week or two once the rings show up.
 
#20
Parts are on the way! Honed the cylinder and cleaned it up, it’ll get new rings and a fresh set of rod bearings. Pulled a reground Star cam out of the donor motor and may use it. Looks like it was lightened and ground for more lift, I’ll have to measure it up to compare to my stock Star cam specs. Can’t wait to get it back together.
 

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