Finally, I'm settled on what I'm building.

ultralight01

ultralight01

New Member
I've gone back and forth between the 79cc, 212cc, a huasheng, and even a Briggs 3hp engine. I have a 212cc predator, but after some discussion with most of the members on this forum it would be rather difficult for a 15 year old (me) to dream of getting such a homebuilt motorcycle legal. For reliable transportation and relatively low cost, it's not worth it st the moment.

Plan is, use the 79cc, put a 33cc sticker on it, and call it a motor assisted scooter. They are legal in Oregon. Add lights and don't be a retard on the road.

I will use a mountain bike, upgrade the wheels, front disc brake, jackshaft disc brake, gear reduction jackshaft plate from GTC, and various jackshaft parts I have. Trying to go for a 11:1 ratio if that will work, I hardly weigh 130lbs.
Governor will be removed. Homemade exhaust, new air filter, drilled jet.

Im undecided on the chain size, but I have 6ft of #41 so I will probably use that. #35 chain for the jackshaft, maxtorque clutch (I already own most of the jackshaft pieces)

Budget $900. The cost will likely be less if I'm thrifty.
 
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Here's some proof.
 
I'd gear it 13:1 instead of 11:1 if I were you. When I built my first predator bike (not the one you saw) it was geared at 11:1 and it didn't have nearly enough power. I'm 155 lb and 13:1 is just barely enough, and I wish it was a little more.
 
I have a Briggs 3.5 hp 9000 series which is used and in good condition that I'll be using with 14:1 ratio on a 26 inch wheel bike that weighs 130 lbs and my self the same.

My more worn out Briggs 3 hp 8000 series I was always using 20:1 ratio and less than that and it would no do the trails as well, as it is only legal off road and I ride it there.

Close to trying it out again with the switched engine an see how it works.
 
16:1 is a good overall ratio. Decent bottom end with a top just shy of 30. I have run 14:1 also. Good if hills don't factor in.
 
I'm adding everything up, looks like all parts to finish the bike. Looks like parts and the engine total will be $500 max.
I'm trying to decide if I should use my commuter Schwinn sierra frame, or I could get a classic Schwinn cruiser frame. Which would be more comfortable? That's what I'm trying to figure out
 
Update. Governor removed, everything else removed.... now I have to figure out an exhaust. I have an intake but no filter to fit around it. Then I'll figure out the throttle. Now I have the rest of the parts for the bike... jackshaft, wheels, handlebars and fork, paint the frame I have, and more
 
I'm thinking of mounting the engine with angle iron. Two lengths of angled iron, both sandwiched with bolts onto the frame. Then I could use the protruding edges to mount the engine with two bolt holes on each side.

Might it work?
 
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Very good.
EDIT:
I'm currently looking for.
Disc hub wheels (26"),
Disc brakes, rotors and brakes.
Quality Sprocket adapters and sprockets.
Mini hubs (2)
Suspension fork (1") and handlebars
The rest, including the jackshaft for gear reduction, the mounting of the engine, and lights I'll be adding or making myself.
 
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Continuing with my steel Schwinn frame.
Got my battery today
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It's 4.5Ah and 12 volts. I'll be using two step down converters to power a (purchased) turn signal kit that runs on 3v, El Stip for light effects, and two 12v 27 watt fog lights. I'm also adding an alternator. Alternators are an interesting thing to me, no one seems to like adding them to their bikes because of cost and expense. I've found a way to add one for about $40 that will be plenty sufficient to recharge the battery.

I feel like this thread should be renamed "My 79cc MTB build," if anyone wants to do that for me.

The battery weights over 7 pounds! It's like a brick of lead. I'm not used to these things.
I'm working on mounting the engine today.

I've ordered a tank, fuel hoses, a valve cover breather, and a 203mm rotor and hydraulic brake.
 
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Here's the Avid Hydraulic brake. It's brand new of course. $24 shipped on eBay. Hydraulic disc brakes are not an expensive prospect if you have wheels with bolt holes!
 
Today I made the Mounting plate out of steel, decided on engine placement and decided on the paint job. I'll post pictures on the mounting plate tomorrow. I need to weld a couple of bends to reinforce it.
 
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