Vanguard engine help

[Bob The Dog]

Mine was doing exactly that a while ago. Popped off the fuel tank, air filter and the metal frame that the air filter filts to. You then have access to the top of the carb. There’s a jet (or whatever it is) that screws into the top of the carb, and mine was well blocked with debris. Gave it a clean, put it all back together and it ran perfectly. Also with these, check that the choke control arm clamp hasn’t come loose. 

[openspaceman]

18 minutes ago, Bob The Dog said:

Mine was doing exactly that a while ago. Popped off the fuel tank, air filter and the metal frame that the air filter filts to. You then have access to the top of the carb. There’s a jet (or whatever it is) that screws into the top of the carb, and mine was well blocked with debris. Gave it a clean, put it all back together and it ran perfectly. Also with these, check that the choke control arm clamp hasn’t come loose. 

That's what I was thinking, an engine that hunts on high idle with the governor opening and closing the butterfly is normally from a blocked (idle) jet. It doesn't explain popping on overrun which normally means some unburned fuel or flame carrying over into the exhaust.

[GA Groundcare]

There is a 90 degree fuel filter under the fuel tank. You need to remove the fuel tank to change it. Have you replaced this? Most folk don't know it is there...

 

Quite a few petrol engines backfire on over run as they become driven by the drum/flywheel when throttling down. You could take the belts off, run the engine and see if it still happens. On a CS you'll need to refit the belt guard to activate the guard switch.

Edited Monday at 08:34 by GA Groundcare

[Ledburyjosh]

On 13/07/2025 at 22:01, Bob The Dog said:

Mine was doing exactly that a while ago. Popped off the fuel tank, air filter and the metal frame that the air filter filts to. You then have access to the top of the carb. There’s a jet (or whatever it is) that screws into the top of the carb, and mine was well blocked with debris. Gave it a clean, put it all back together and it ran perfectly. Also with these, check that the choke control arm clamp hasn’t come loose. 

The choke is loose, and a bungee holds its back. On the list to tighten.

 

I'll check out the things on top the carb. 

 

Ta,

[Ledburyjosh]

On 14/07/2025 at 09:34, GA Groundcare said:

There is a 90 degree fuel filter under the fuel tank. You need to remove the fuel tank to change it. Have you replaced this? Most folk don't know it is there...

 

Quite a few petrol engines backfire on over run as they become driven by the drum/flywheel when throttling down. You could take the belts off, run the engine and see if it still happens. On a CS you'll need to refit the belt guard to activate the guard switch.

A little black round thing?

[GA Groundcare]

15 hours ago, Ledburyjosh said:

A little black round thing?

No, its a clear/white plastic 90 degree filter.