Surging Lawnmower

[jj4091]

It might be totally unrelated but just had a similar fault with a strimmer with the same carb as yours. Tried replacing it with a new one but only made a slight improvement . I removed the carb. again and the spacer behind it so that you could see into the barrel easily. the piston when slowly moved up and down with the pull cord (spark plug removed) appeared to have lost a ring. The owner declined spending any more money on it so not sure if that was a problem or not but I suspected that it was not drawing in enough fuel from the carb. because it had a broken ring that had dropped into the sump.

 

[WhoMe?]

When the engine is running, fuel is sucked from the carburettor float chamber, not the fuel tank.
The float chamber is refilled from the tank, and regulated by the needle valve which in itself is controlled by the white plastic float.
Nothing needs to be adjusted, drilled or bent.....this will come back to haunt.
When the engine surges, it is short on fuel. As the revs drop, the governor opens the throttle to compensate so the revs go up and down.
I can’t say if the internal governor is working or not, all I can say is that I’ve never had one fail.
I’m getting a little lost here.....can you get the engine to idle at low speed by adjusting the black plastic idle screw, or does the governor not let you?
John

Whatever position the idle screw is in, the engine surges. I was just wondering that, if everything from the tank to carburettor appears fine, even with the new carburettor before I tampered with it and it still surges, is the fault somewhere else, like the other guy said:

It might be totally unrelated but just had a similar fault with a strimmer with the same carb as yours. Tried replacing it with a new one but only made a slight improvement . I removed the carb. again and the spacer behind it so that you could see into the barrel easily. the piston when slowly moved up and down with the pull cord (spark plug removed) appeared to have lost a ring. The owner declined spending any more money on it so not sure if that was a problem or not but I suspected that it was not drawing in enough fuel from the carb. because it had a broken ring that had dropped into the sump.

It was fine last year and then I foolishly left fuel in it over winter. Then first use this year, it started with this problem. Could the fuel have clogged or deteriorated something inside the engine? But you guys know a lot more than I do.

Thanks

 

[Harry Bloomfield]

It was fine last year and then I foolishly left fuel in it over winter. Then first use this year, it started with this problem. Could the fuel have clogged or deteriorated something inside the engine? But you guys know a lot more than I do.

No, old fuel simply gums the carb up.

 

[Stivino]

No, old fuel simply gums the carb up.

I've left the fuel in mine over winter for the last 22 years and never had a problem.

 

[Harry Bloomfield]

I've left the fuel in mine over winter for the last 22 years and never had a problem.

Likewise, never a problem with any of mine, ever. Just what others report, and manufacturers suggest.