Dave, your numbers are close. 12T front sprocket and a 9" diameter rear sprocket with 72T. Both rims are 7" in diameter. Tires measure 12". As for the governor, I don't think it's in the case. I'm not sure. Can the governor arm still swing with the throttle arm? That's how it's set up. I can get a pic of it for you. It's crappy out today, but I will get a top speed for you soon.
Endo, there are on line calculators for computing your "maximum speed." It uses the sprocket teeth, the total diameter of your rear tire, then finally, it uses your maximum RPM. Easy to Google it.
Normally, these Tecumseh engines are governed via the throttle arm against spring resistance, and the spring is hooked to another arm that operates off of centrifugal force from some spinning weights inside the engine. That governed RPM is generally around 3500 maximum. If you go much over that, you have a real good chance at breaking your connecting rod on this engine. Other engines commonly used on mini bikes, both old, and new, have other things that break if RPM is exceeded, and some of those engines have after market parts available to prevent that from happening as easily. There is a Tecumseh manual as a sticky on this forum under the "Tecumseh" section, and among other things, the governor system is described.
I don't need to know your top speed. We've just been doing this for awhile, and know what we're looking at. No offense intended. I happen to be a fan of Tecumseh engines, and along with a few others, we have the operating parameters figured out.
That clutch brake system has a lot of fans. It is easy to install and works quite well to stop a bike. However the guy who actually makes mini bike clutches- or I should say, the guy who makes Max Torque clutches, is totally against using them as a brake. The reason for this, is that heat is the enemy of those clutches, specifically the "oil lite" (Oil impregnated) bronze bushing that serves as the bearing. A brake not only heats that up, but applies a torsional load on them, further wearing the bushing. Most people here will tell you not to worry about it. If I were sitting there with a vintage drum brake, I would definitely fix that. Probably take it apart, and clean it well, source some shoes if required, or maybe they just need a light sanding. The clutch brake is way better at stopping the bike than the drum will ever be. But I wanted to point out the Pros and Cons.
I would also use a jack shaft. That is what those holes are for. That will allow you more latitude in making sprocket changes, and fine tune the gear ratio for decent speed, with decent torque.
Obviously the bad thing about using heat on your drain plugs, is the oil boiling inside. In all the engines I have done, only once have I had a drain plug I could not remove. I welded a piece of steel to it, and hit the steel with a hammer. You only need to remove one of those drain plugs.
I apologize for the extremely long post here, but figured I'd make it up for my initial terse reaction to your speed claim. Your best friend is probably Google searching this site. All of the information you need is here, but you have to find it. Find some posts with Bonanza's like yours, and PM the author. A lot of people here are Bonanza fans, and like most of us, will go out of their way to help a new member who wants to learn, and help himself.
Best of luck, and welcome to OldMiniBikes Forums.
