Surging Lawnmower

[Burnerman]

Here’s a wee test.
Hold the governor rod by hand, so the engine runs slowly. If it tends to stall, screw in the idle screw to keep it running.
If all is well here the engine will continue to run with no issues.
Then, hold the engine at high speed, using the governor rod. ( you’ll feel the rod trying to fight you here).
If the engine is short on fuel, it will tend to splutter and fail.
John

 

[WhoMe?]

may not be helpful
but have you replaced all the fuel from last year
are you using E5 / 95% 97% or E10 ???
unlikely but thought i would perhaps mention .....

Yes, last weekend when the issue started. Before that it was a couple weeks old

'The bit at the bottom', probably. The weights are flung out, under centrifugal force, which then closes throttle. The surging, and the video suggests that there is an issue of sticking governor.

Is that nut at the bottom left of your photo done up tightly to prevent the mechanism from moving on the shaft?

Thanks both, I'll take a look

 

[WhoMe?]

Here’s a wee test.
Hold the governor rod by hand, so the engine runs slowly. If it tends to stall, screw in the idle screw to keep it running.
If all is well here the engine will continue to run with no issues.
Then, hold the engine at high speed, using the governor rod. ( you’ll feel the rod trying to fight you here).
If the engine is short on fuel, it will tend to splutter and fail.
John

I did this. Hold it one way it stalls, the other way it fights me and revs high

 

[Burnerman]

If the engine stalls when it’s trying to run at low speed......
Turn the tick over screw clockwise to keep the throttle open;
If it still stalls, it’s a pilot jet blockage or adjustment required. Some are adjustable, some are not and we’ll need a picture or two of the carb to sort that one.
Interesting, this one or you may not agree!
John

 

[WhoMe?]

Thanks for all your advice. I'll have to find some time this week between work to take a look

 

[Burnerman]

Stick with the diynot heroes and we’ll get there.....

Probably!

John

 

[WhoMe?]

Thank you, I just hope I've not done something stupid

 

[WhoMe?]

Hi

The saga continues

More parts bought and it still continues, although surges a bit faster. I've changed the fuel hose, all the gaskets (3 more between carb and engine), and new spark plug even though last was not that old.

I did your test and it still stalls with idle screw all the way out. I've attached pictures of the carb. I've already made the fuel jet hole a little larger. Any more suggestions would be great.

Thanks

 

[Harry Bloomfield]

I've already made the fuel jet hole a little larger.

Jets in carburettors and etc. are precision drilled to accurate dimensions. If you have made the jet larger, then it is completely ruined.

 

[WhoMe?]

Possibly, I did what many online have said to do. Maybe I unknowingly fixed the issue but caused another. Before I enlarged the hole it was surging. Same as previous carb.

Still seams not enough fuel is getting into the carb as even when warm I have to prime it to restart it.

 

[Burnerman]

There isn't actually an idle mixture screw so can you see the black plastic rectangle below where the idle screw was? Thats the idle jet so prise it out for a clean.
John

 

[WhoMe?]

There isn't actually an idle mixture screw so can you see the black plastic rectangle below where the idle screw was? Thats the idle jet so prise it out for a clean.
John

Oh, I thought that is the black screw over the idle jet. I'll do as you suggest.

Thanks

 

[Burnerman]

Once you've prised out the jet you'll see drillings that go to the outside of the carb(small separate hole alongside the main venturi) and the opposite way to a tiny hole in the carb body.
These need to be perfectly clear.
John

 

[WhoMe?]

Still no progress and I'm about to admit defeat and buy new.

It couldn't be anything to do with combustion could it? Am I right in saying that the combustion sucks more fuel out of the tank, so maybe it's not sucking enough? Could I spray carb cleaner into the manifold (if that's what it's called. The hole from the carb into the engine).

Thanks

 

[Burnerman]

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