79cc motorbike build questions - thanks!

MotorBikeFab

New Member
Joined
Sep 9, 2018
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19
Building a 79cc Pred Dyno motorbike. This is going to be a street bike for my father (me) and son motorbike project.

Here are some pics:
https://motorbikefab.com/79cc-predator-project-motor-bike-fab/
and pics below:

79cc_1617.jpg 79cc_1619.jpg 79cc_1630.jpg 79cc_1632.jpg
79cc_1612.jpg 79cc_1623.jpg

Which throttle should I get?
I see some with a 90˚ wheel and some without. Which do you prefer and why? Which vendor do you recommend?

Which fuel pump do you recommend and why? Vendor?

I got a 19mm Mikuni for this project and am wondering what the jetting should be and where to get the jets?

I am building an exhaust manifold/header and want it to exit behind the rear axle. What muffler do you recommend? This is going to be a street bike for my father (me) and son motorbike project.

I need about 12" or 305mm to clear the full width of the engine pull start on one side and the cent clutch on the other side...what are you doing to get this width? Or what is the widest bottom bracket for 68mm that you have found? I will get the American to standard tapered cassette bottom bracket adapter. If there is no really wide BB which cranks do you recommend for bending or cutting and welding to make them work? Which vendor?

I am thinking of drilling and tapping for a fuel pump vent pulse in the area on the PTO side that looks like it was meant to be for a filler or the like, but is blocked off in the casting. I am planning to drill and tap for the brass fuel line fitting and can also use it to fill oil at oil change time. Any thoughts about this?

I know I will have more questions soon! Thanks so much for your help.
 


JerboaJohn

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Jul 29, 2018
Messages
900
so many questions! break it down; this is too much for 1 topic lol.
for a throttle there is too many choices! I like to pick a throttle and get the grips I want separate
 

Will'smotobikes19

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Apr 9, 2018
Messages
1,425
You must be tall that seat tube is really high. I think mbrebel has the wide crank kits. Way better than the Chinese wide pedal kits. I just got an 80’s 3hp flathead briggs for free. Wonder if I could do a build with it. Where is the gas tank going? You shouldn’t need a pump as long as the gas tank has gravity moving the gas.
 

MotorBikeFab

New Member
Joined
Sep 9, 2018
Messages
19
79cc_1609.jpg

The pic shows the orange oil filler plug and the unthreaded boss for another oil filler option. The thread for the oil filler plug is 3/4-10. I have some inexpensive 3/4-10 carbon steel taps coming to thread the unthreaded boss at the top of the crankcase and 3/4-10 bolts to plug what will be the drain plug. The oil "dip stick" will not work to measure the correct amount of oil...but that is a non-issue. The taps are coming on Monday and I will post pics of the finished product later next week.

Also, moding the frame in the area behind the bottom bracket shell to make fitting a dual leg center stand possible...pics to come next week.
 

curtisfox

Active Member
Joined
May 13, 2010
Messages
618
You could add a rod inside the new cap, get the right amount of oil in it and mark the rod. Then there will be no fear of overfill...........Curt
 

JerboaJohn

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Joined
Jul 29, 2018
Messages
900
I'm using mounts like that, but not vertically lol. mine doesn't have beveled edges but Gasbike has em for the best price on the site, like $60
 

curtisfox

Active Member
Joined
May 13, 2010
Messages
618
You can bevel your own with a router and carbide bit, work on metal just like it does on wood..............Curt
 
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