Rev-limiter on Chinese "Happy Time" 80cc?

chrisnbush

Member
Joined
Apr 9, 2008
Messages
135
Going back to the original post, you may have an air leak

I installed the 80cc motor kit on a nearly new mountain bike. Everything is straight, well lubed and runs true. After about 100 miles I decided to test the top speed. Up to 25mph everythings great. Plenty of throttle left and when fully open engine sounds like it is going to gain speed rapidly. After about 27mph the engine acts like it is being controlled or held back by some kind of restrictive device. My son in law has the same engine kit and it responds the same way. I have installed a new carbon plug wire, plug and carb. o-ring. I modified the muffler by removing baffles and cutting the small exhaust pipe to about 3 inches. I would appreciate any ideas or suggestions to engine can continue reving. Thanks, Mike
This happened to me, the carb manifold gasket is **** on a lot of these, as described in any number of posts. Engine cuts out, loses power at higher RPM. Maybe this is it ?

On my first build (no name CH80) I used some permatek oil resistant gasket stuff which fixed it, but looked like ****.

Got my second engine (1st blew up after 1500 miles, upper roller bearing cage broke, cheap cage - looked like stamped steel) from DAX, and am hoping the gaskets are improved. This engine seems to run a lot smoother...

Chris
 


Mountainman

Active Member
Joined
Jun 15, 2008
Messages
3,579
over rev -- sure it's possible on some 2-strokes

you should not be able to over rev a two stroke and start breaking your engine
not to sure about that

yes - many 2-strokes are engineered so as to not
over rev -- blow themselfs up

but - I have owned many over the years
that if not watched over by me
so as to not be red lined too long
WOULD TEAR THEMSELFS RIGHT OUT OF HERE -- in no time

ride that thing
 

garyj

New Member
Joined
Jul 16, 2009
Messages
5
Revs&MPH

I have a Zoom Kit 68cc,I think it's 38tooth rear, I have trouble turning around in the street without pulling in the clutch, leading me to believe that I have the smaller higher MPH rear sprocket. Anyhow my speedo set to a 26' wheel shows comfi cruise at 28-30, top speed around 39MPH, I just don't have the guts to go any faster. The engine pulls a 225lb rider/me from idle to 25MPH, stumbles & requires a bit of moving the throttle in & out a bit then screams to whatever speed/Vibration you can tolerate, 35-39. Ordered the new carb hope its smoother.
 
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duivendyk

Guest
What is your overall gear ratio ratio?.To come up with speed use S=0.075x rpm/R (26" wheel) S speed mph, R total reduction or engine reduct. x 44/? .For instance,Engine reduct. 4.5 ? primary sprocket 11T .S=0.075x 6000 /(4.5 x 44/11) =450/18 or S=25mph .The internal engine reduction is a guess,as is the 11T primary sprocket size.
 

garyj

New Member
Joined
Jul 16, 2009
Messages
5
I have not counted the teeth but did a blast today with the new style carb with the petcock on it, & bigger intake & jet, it pulled a bit better, so I increased the amount of oil in the fuel to counter the RPM & heat, it pulled strong at any throttle setting, to 25MPH, then required releasing/twisting/ a bit closed, then opening slowly as RPM increased, I held on to about 35MPH, sounded like 7000 RPM or more. The carb started leaking then I guess either the float needs adjustment or a piece of dirt got in the needle & seat.
Love hate relationship continues.
 

arceeguy

Active Member
Joined
May 20, 2008
Messages
1,157
......it pulled strong at any throttle setting, to 25MPH, then required releasing/twisting/ a bit closed, then opening slowly as RPM increased, I held on to about 35MPH, sounded like 7000 RPM or more......
Danger! Danger! Will Robinson!

Sounds like a good description of "lean bog" at high rpm's. Certain death for a two stroke engine, regardless of how much oil you put in the gas. Looks like you'll need to go a size up on the main jet. Even then, I wouldn't condone 7K RPM on a HT engine for anything longer than short bursts.
 
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duivendyk

Guest
If you don't know your overall reduction it just guesswork what your rpm is.If you care at all about engine life,it's advisable to stay below 6k.
 

garyj

New Member
Joined
Jul 16, 2009
Messages
5
I'd love to know where I could purchase jets?? Blasts/high RPM, are 10seconds or less, because of Vibration etc, I understand any extended cruising would be at 25-29MPH for my ratio? the Sound /Rpm seems manageable. I have extensive, cam/carb, auto experience, & run nitro/methanol plane engines, they idle @ 3300, & go to 15,000 RPM, you get to know what is & is not OK RPM the first year you run these things. I'm a bit bummed out that I have to take my new carb off & set the float/ check for dirt, 15minutes of use!!! Oh well
 
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motorisedbikehoonage

Guest
I installed the 80cc motor kit on a nearly new mountain bike. Everything is straight, well lubed and runs true. After about 100 miles I decided to test the top speed. Up to 25mph everythings great. Plenty of throttle left and when fully open engine sounds like it is going to gain speed rapidly. After about 27mph the engine acts like it is being controlled or held back by some kind of restrictive device. My son in law has the same engine kit and it responds the same way. I have installed a new carbon plug wire, plug and carb. o-ring. I modified the muffler by removing baffles and cutting the small exhaust pipe to about 3 inches. I would appreciate any ideas or suggestions to engine can continue reving. Thanks, Mike
You will just have to adjust the fuel mixture easy as
 
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