HuaSheng 4t miss firing

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yodabob

New Member
Jun 29, 2008
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North Wales PA
HuaSheng 4t miss firing during a ride the other day. Still has power but acts like you are tapping on the kill switch when riding.
Disconnected kill switch same thing. Changed plug wire same. Changed plug (color was good) same. Removed and broke down and looked in carb and cleaned all jetting, checked float plus free flowing gas from tank same. Changed magneto same. Seems to get worse with air cleaner on. Anyone got a clue before I rip the motor apart?

Yodabob
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stevolandis

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Feb 20, 2010
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NE Pennsylvania
Maybe the exhaust or the carb is loose from the engine(causing an air leak). My engine did the same thing, it acted like it grounded out, but then it ran a little, then shut off, etc. During this, my pipe was clogged, so I fixed that, and then my intake was loose. when I fixed them, the engine acted normal, so I'm not sure which fix it. I would guess the loose carb. This would let air into the engine, and leaned the mixture a lot. The engine then couldn't fire.
Try your intake.

Hope it works!
 

yodabob

New Member
Jun 29, 2008
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North Wales PA
Had already checked carb and had taken it off and gone over it and replaced it. We did find the custom air cleaner soaked with oil that had been working for 600 miles, which would cause choking. So we made up a pressure test set up on the bench. Locked the fly wheel with piston at TDC and both rocker arms with valve clearance. Took it up to 80 psi and had no blow by in the crank case. Slightest leak at exhaust valve, intake ok. Don't know why the oil got in air cleaner. We will run it on the bench tomorrow to see if problem still exists. Because everything we have found so far says it should run fine.


Yodabob
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Bikeguy Joe

Godfather of Motorized Bicycles
Jan 8, 2008
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I will mention that a leak on the exhaust valve side is no good, mostly for the valve. I don't think it would cause an intermittent miss though.

Each time it "misses"- how long is that for? A split second, or a longer period?
 

yodabob

New Member
Jun 29, 2008
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North Wales PA
The missing is split seconds. At lower rpm's you can just make it out but it is still there.
Well bench tested and still popping. Changed carb and fuel still popping.
Now we will break the motor down and check the valves in the guides and change valve springs and lap exhaust while there to see what happens. This proving to be a fun one????????


Yodabob
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yodabob

New Member
Jun 29, 2008
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North Wales PA
Well took motor apart and found oil slinger was broke that I wasn’t happy to see, did not cause any damage. Still shouldn’t have had anything to do with the missing. We decided to use cylinder and valve assemble from another motor that the rod cap had fallen off of. From the motor that was missing we used the crank, rod, piston, magneto, plug, carb, and flywheel and it runs great now. Remove the valves from the motor that was missing and both had a real nice looking seating mark. Can’t believe that the slightest leak that the exhaust valve had caused the problem. To show how little the leak was, under 80 psi spraying bubble leak in the exhaust port did not blow out but slowly formed bubbles. I’m sure down the road it would of caused a problem. Almost apt to believe that there is a crack in the block somewhere but I’ll be darned if we can find it.


Yodabob
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