I started thinking I'm going to go with a 4HP briggs my friend converted from a lawn mower and has been working on.
It's converted to run up-right. It's super light weight, and appears it'll fit in my frame no problem. Esp with the rounded edges at the bottom I may beable to have decent clearance from the top bar of the frame. I'd guess no more then an inch and a half though hehe.
I'm still on a budget, I may beable to score the motor for 20. However if he wants to keep it I'll just have him get some lawnmowers and we'll get a bunch free/cheap. It's how he got this one.
The shaft is 7/8ths
I don't know what direction it turns off hand.
I'm going this route for various reasons.
1) Goal is getting a modular style jackshaft setup, and probably get someone to mill the shaft down to 5/8th to run a easy to obtain centrif clutch jackshaft setup.
2) The goal of modular style setup is I do want to maybe put a suspension fork on this, but in my area they don't care if you run scooter style pocket rocket things and what not that aren't legal, and 4 stroke chopper ones. Just don't act like an idiot. I don't care to go faster I just want to go the limit good, and beable to hit trails. Not a chopper style but probably one of those mono shock bikes people buy that I think come with in-frame gas tank too from a few companies. So I'd like to be able to remount the setup much as possible.
3) as bike comes along I decided for the first frame I got now I will go till it breaks, so a few hundred bucks is fine initially, I'm prepared for what the 4 stroke will cost but I have other plans.
4) I am currently working on getting a 2cyl compatible FreeEMS board made in 3-6 months or so. Why 2 cyl? I want it to beable to run 1 or 2 cyl, 1 at first probably ignition only and a carb which is nice. Then as I go FI or maybe before depending, I will get one of those tiny turbos. I have been told they dont like 1 cyl, 2cyl vtwins stock weigh a lot. This brigs I am possibly getitng cheap weighs nothing, so double and a custom crankcase and what not should not be much more, slightly less then a stock v-twin possibly. I am going to look into that but I will probably risk 1 300 dollar tiny turbo as many on you-tube seem to run them. As I am writing this in steps, that is towards the finalization of the 2nd re-incarnation of the bike where it runs with the 4hp 4 stroke fine for months. Once I hit that and computer ignition, as I do with cars, I'd love to turbo.
5) I'd like to not stop there. As many have read I have been planning a hybrid e-hub electric setup, well before my ghetto 33cc setup. So I have been thinking I will also attempt like a volvo engine I've seen with a supercharger, and twin turbo's, plumbed together. I believe the supercharger into the turbo's inlets which pre-spun them sort of. I will have to check into that, however it was a beast. I have seen lots of air pumps tested as superchargers even mounted on go-karts, often FC3S RX-7 smog pumps and GM which do put out a lot of air, and require minimal modification. If I can some how run a aux shaft off the crank like some 4 strokes do for various reasons (Drive) and gear it right to run a alt and smog pump at idle fine. It should have quick rev'ing regardless of where the smog pump is plumbed in the intake piping. Then you would want to take it easy, of course you'd want to look into higher rpm. After lots of googling tonight you can make briggs flat heads take over 8psi of boost around 4-5k rpm and apparently you can make briggs rev high, people say they blow but thats when you introduce certain conditions. Now I would prefer a water cooled 4 stroke but I currently know of none, and I don't want to add that into the mix yet. I will however do what I have not seen, and when I do a boosted 4 stroke I will do meth injection.
I could go on, and I'm not for any purpose but boring people. I want to accomplish each step, show you. Eventually get a camera setup, and potentially trailer that will have a laptop to datalog the FreeEMS ignition, then FI, etc. So if I add cams like I used too with my cars I'd just add decent webcams even. I'd like to do that by step 2 or 3 or so as this would be very interesting.
A jackshaft gearbox would be added somewhere down the line, with the boosted application, esp with higher rpm it may let the 4HP alone produce 10-14hp and shift, along with a e-hub motor. I'd def need to get a stronger frame thus I probably wont boost on this frame. It feels solid but is weaker then Specailized Hard Rock, and my regular rim in the front and it seems the heavy duty rim in the back are already bending from under 30mph 33cc power....I also will be doing disk brake setup before it goes much faster.