# Baja 196 (?) cc chinese bike. starter kicks back



## luckyvision (May 24, 2007)

working on a friends chinese-knockoff kids 'chopper' with basicly a lawnmower engine.

when you pull the starter it can kickback violently. there is some carbon on the piston, but not a ton, the plug was black but not thick. the oil level was kind of high. i'm wondering since neither of these were really bad, if the combination is enough to raise the compression too high 

i didn't do a compression check (didn't think of it) & i didn't check the flywheel key, but from the end it looked 'normal' 

should i pull the flywheel?

anything else that would cause it?

the handle is broken so it'll get replaced., but wrapped in a rag & 'preloading' the starter to the compression point, the bike will start.

also, possably unrelated, i think the clutch springs are streched. it's hard to hold the tire at idle.

Thanks, --Lucky


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## 30yearTech (Sep 14, 2006)

Is it an OHV engine? If so, the valve lash may need to be adjusted. OHV engines need adjustment about every 50 hrs or so. Too much valve lash and the compression release will not work properly and cause excessive starting compression. 

A sheared flywheel key could also cause this due to ignition timing being too far advanced and causing the engine to try and fire over backwards.

Best of Luck... :thumbsup:


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## luckyvision (May 24, 2007)

I wasnt aware of a compression relese. it's not a very sofisticated (?) engine


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## 30yearTech (Sep 14, 2006)

luckyvision said:


> I wasnt aware of a compression relese. it's not a very sofisticated (?) engine


Most all 4 cycle engines will employ some type of compression release. OHV designs are generally easily adjustable.

Do you know if this engine has overhead valves?


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## luckyvision (May 24, 2007)

I'm waiting for the owner to email me the parts fiche, but i'll go ahead & pull the flywheel anyway.


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## 30yearTech (Sep 14, 2006)

luckyvision said:


> I'm waiting for the owner to email me the parts fiche, but i'll go ahead & pull the flywheel anyway.


I suspect your engine is much like this one:

http://www.harborfreight.com/manuals/66000-66999/66015.pdf

If so, then I would suggest checking the valve lash on both valves. 

You can use the specs listed on this engine, as it should work fine for the one your working on also. 

Be sure to check the lash at or about 1/4" past TDC of the compression or power stroke of the engine.


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## luckyvision (May 24, 2007)

That's the one!

why 1/4" past tdc? (measured from the outside edge of the flywheel?)

with the plug in you can feel tdc, but this is interesting: on most single cyl engines if you turn the flywheel by hand, when you get to tdc on the compression stroke, cou feel it compress then eas up. kinda ramp up, ramp down. 

on this engine it's more like ramp up, flat spot, (you can wiggle the flywheel ccw/cw/ccw) then ramp down

the flywheel is not loose on the shaft & i don't believe there is play in the connecting rod, etc.. is 54mm a particuarly long stroke?

I'm not seeing any compression release on the diagram either. i don't remember ever seeing on on a briggs type lawnmower engine.. care to point it out?

Thanks! --Lucky


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## 30yearTech (Sep 14, 2006)

You generally won't see the compression release in the IPL's of the engines, as they are an integral part of the camshaft. The compression release is usually not serviceable, if it breaks then you have to replace the complete camshaft assembly. Some engine's utilize a "bump" type release, which just amounts to a raised portion of the lobe. ( The illustration in the manual does show the mechanical release on the camshaft if you enlarge it enough. You will see the flyweight on the camshaft, as well as the return spring and the pin in the lobe of the cam that lifts the valve)

Top dead center if fine for setting the valves, 1/4" past just insures that the compression release is not engaged any, as it should not be at TDC either. 

If the valve lash is set properly, then you can see the compression release in action by slowly rotating the engine and watching the valves. One valve will lift slightly during the compression stroke to bleed off a little compression and then close again just before TDC. At running speeds the compression release deactivates so the engine can produce full compression.


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## luckyvision (May 24, 2007)

That's interesting, all the engines i've pulled apart, i've never noticed it...

hard to tell from the illustration, but the piece on the inside of the cam gear, that looks reminicent of a breaker plate.. this controlls the pin? looks like centrifigul force would move the plate outward, against spring pressure, & allow the pin to drop back into the cam lobe. am i surmising that correctly? ingenous! lol


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## 30yearTech (Sep 14, 2006)

Yes, that's how it works. As the engine rpm's increase centrifugal force causes the flyweight to move out and the pin drops into the cam lobe disengaging the compression release. There are different designs to this but all basically operate the same way.


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