First Build, 4-stroke 3.5 hp on a Schwinn Bike

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lowracer

lowracer

New Member
Oct 17, 2008
1,319
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Charleston, SC
Kristof,
I live in a flat area.
There is a great gear calculator either on this website or the 'other' MB site.
I use it all the time & can compute the full range of Speed to RPM's for my engines.
I do have a different size tire (1.25 not 1.9) than I posted earlier but it doesn't change the #'s much.
Here is what I come up with using the gear calculator for my setup & its very accurate.
1200 rpm = 12 mph
3000 rpm = 30 mph *max torque*
4200 rpm = 42 mph *max HP*
I do pedal a little to get it rolling along & put less stress on everything.
Hope this helps.
-Lowracer-
 
lowracer

lowracer

New Member
Oct 17, 2008
1,319
2
0
Charleston, SC
Nice thing about using a jackshaft is you can mount your engine perfectly centered & use the jackshaft to compensate for chainline.
Lets see pics once you get it underway...
-lowracer-
 
Kristof

Kristof

New Member
Jan 21, 2011
232
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Aliso Viejo, CA
I wish I could make time go by faster because it will take at least a week for the package to get to my place and then I have to mount it on.
 
E

Erich_870

New Member
Dec 4, 2009
78
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Alaska
Just a couple comments. Overall it looks good, but the weld at your frame clearancing needs to be ground out and redone. Something was wrong with your welder when you did that one; maybe you didn't have the shielding gas on your you didn't grind off the paint, but those pits show that it's a very dirty and brittle weld. Better not chance your life with that.

Secondly, I'd add a triangular brace under each jack shaft leg. You're welds are in tension on the cross member and it would be safer to add a compression member under the rectangular tubing.

Erich
 
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Kristof

Kristof

New Member
Jan 21, 2011
232
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Aliso Viejo, CA
UPDATE 1.1

I put the smaller chain on, but it took forever. I had to take whole engine off again... and then elongate the holes so I can move the engine towards the rear and then finally put the master link on.

 
G

Gator Wrestler

New Member
Jan 22, 2009
124
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Springfield LA
If you have any plans to climb hills I think you will find that the gearing you have will not work very well. However it is simple to change the ratio by using a higher tooth count sprocket in place of the 14t that's driven by the clutch. If a 20t is used the ratio will be 12 to 1. You may even want to go higher for more hill climbing torque. I could be wrong I havn't used that engine. The 2.5HP HF works well with a 12 to 1 ratio but doesn't have hill climbing torque. YMMV.
 
Kristof

Kristof

New Member
Jan 21, 2011
232
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0
Aliso Viejo, CA
I rode the bike today and it was awesome!!!
It's limping because it needs a new diaphragm, but man it was awesome!

I don't have a throttle either, so I was reaching back the whole time to control the throttle via choke handle.

I will upload pictures soon, but I will try to rude over to a Lawnmower repair shop.
 
scotto-

scotto-

Custom 4-Stroke Bike Builder
Jun 3, 2010
6,505
24
38
Ridin' inSane Diego, CA.
Yeah baby......great to hear that!!! Shouldn't be to hard to rig a decent throttle and get a carb kit for the diaphram. Keep it coming, you are there!

dnut
 
Kristof

Kristof

New Member
Jan 21, 2011
232
0
0
Aliso Viejo, CA
Today, I limped 11 miles to the small engine repair shop and I bought the diaphragm for 5 bucks. I installed it myself right on the spot and tried to start it but the idle mixture screw was not responding. So the owner of the shop was nice enough to give me a hand and he and his assistant worked on the carb. for at least 2 hours. It turned out there was some clogging in the jets.

Then he rigged some sort of rope to the governor so I don't have to reach back with one hand all the way back home. The rope worked out pretty well as a throttle control.

Now, to talk about speed and torque. I don't know much, but it seems it has enough torque, but on a flat road I only reached 33mph. =[
Downhill only 37mph.
 
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Goldy

Goldy

Member
Oct 3, 2010
196
15
18
Nova Scotia
Gotta love those controls..crude but effective! :)
As far as top speed goes, for a 3.5hp engine, that's pretty respectable. Probably just about all you are going to get without sacrificing torque, but that's just my opinion...you could always try fiddling around with your jack-shaft sprockets to try out different ratios. Figure out what suits you best.
 
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