Stumbles at full throttle but only with light load.

Hi Fish - I had the solenoid out the other day to check and see if it was working. I caught most of the gas in a small cup and didn't notice any problems. I took the solenoid out again this afternoon and made sure I caught all the gas this time. The gas was clear and clean. No water, debris or anything.


Ed
 
Yeah, didn't cost any money to check it.

Water can sit in the bottom of the bowl, and it will run fine until you turn, stop, jiggle etc..,

Then a bit of water sloshes up and gets sucked into the engine.

So when it starts acting up, it will run better if you partially choke it?
 
This one doesn't have a separate choke control. It's integrated into the throttle control. If I gently start nudging up the throttle past full (into the choke zone) I seem to often be able to get to a point where it runs better. But it is really touchy. Not enough and it still runs rough. Too much and it starts to stall out. The difference between the two in throttle movement is tiny.


Ed
 
That tends to indicate a low float bowl fuel level a partially blocked main jet or partially blocked bowl vent.
In the top of the float bowl there should be a hole .
On most carbs it leads to another hole at the engine flange.
This is the hole that allows air to get into the float bowl so the fuel can get out.
When the throttle is open wider, the suction at the main jet is strong ( it gets called "signal " by wan#@$%" trying to sound superior ) .
Thus if the air vent is partially blocked it is strong enough to drag air in
When the "signal" is low there is not enough pressure to drag air through so the engine runs a bit lean
A stuck open reed valve on the breather can also divert a lot of air at lower speeds causing a stumble

When i get stuck I drag out the colortune ( a Gunsens product, Google it ) thus I can just watch what is happening in the combustion chamber
 
Problem solved.

I removed the carburetor. It was really clean inside. Almost looked new. I didn't see any debris or blockages, but I took everything apart and I blew everything out with compressed air. The main gasket was expanded, so I shrank it back down by boiling it for a couple of minutes and then putting it in the refrigerator for a couple of minutes.

Put everything back together. It started right away and ran great.

I never did identify the problem, but something I did in the process must have resolved it. Maybe some tiny bit of debris somewhere I couldn't see got blown out.

Just glad it's working again.


Ed
 
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