Slapping a new motor in?


Local time
1:05 PM
Jun 4, 2008
I am thinking about sticking one of these on my bike

i measured that with the furl tank and air filter removed it will fit in the frame of my mountain bike.

I found a clutch that will fit the shaft of this engine.
is 6.5 hp too much?
6.5 is too much to be legal, and it may be more than you need.
Legal? don't you have a 140 cc engine on your bike?

The problem with that type of engine is that they develop
peak power at 3600 rpm and only rev to about 4000

Where as the GX50 Honda revs to 7800 rpm

i think you would need a jack shaft to get the gearing in the
right range
What clutch do you have in mind?
Mine's not 140 cc, but I'd be about the last person to be judgemental on that subject, I was just pointing it out.
I think you make a good point about the power and rpm. Perhaps it would be a good candidate for a variation of Ghost0's jackshaft? That way, gearing could make up for a limited rpm range.
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I have one of those engines, and it was too big and heavy for my bike, so I made a trailer. But my bike has dual shocks and no room for a frame mount.

If his bike will fit it, it's worth a shot. I'd like to see a 6.5HP engine on a bike! :eek: :devilish:

The stock RPM range is narrow, but with high gearing you will get your speed, and plenty of torque too. If you want more RPM, then remove the governor to get 5000+RPM and run on premium fuel.

It's not that hard to get 40-50mph with that engine! I'd recommend a jackshaft for double-reduction, or a huge rear sprocket because bike tires are so large.

A trike I built with 20" wheels with an 8:1 reduction tops out at around 35mph or so. If you kept that same reduction on a 26" bike, you will go much faster! :devilish: