Brigg Stratton Quantum XM50 smoke and won't rev on lawnmower

[Jonny Vee]

Got a mower with Brigg Stratton Quantum xm50 which smoke black and won't rev.

I cleaned up the carburetor but nothing had changed.

 

[Burnerman]

Make sure the choke flap is fully open ( if it has one).
If not, does fuel flow out of the engine at all?
John

 

[Jonny Vee]

No choke flap and plenty of fuel.

 

[Burnerman]

This small side valve engine has a multitude of guises, some have manual chokes, some automatic, some with none at all.
I'd guess yours has a red primer button on the front......pressing this shoots a blast of air into the carburettor which causes fuel to shoot out of the main jet, allowing a cold start.
Anyway......if your engine is throwing out black smoke then there is too much fuel;
If the smoke is blue then it's an oil issue.
If the machine has been on it's side the air filter may well be ruined so try running the machine without it (one screw lets the cover fall off.)
If all is ok there, perhaps the main jet has become dislodged from the guts of the carb....its float bowl off to check for this one.
Does fuel drip from the engine when it isn't running?
John

 

[chainsaw_masochist]

Could maybe whip out the sparkplug and give a good clean...perhaps even replace altogether.

 

[Jonny Vee]

Could maybe whip out the sparkplug and give a good clean...perhaps even replace altogether.

Done a good clean with no sign of improvement. Can try to get new one. Do you know correct model in case they put wrong one in.

 

[Bodgedbuild]

If it's black smoke and therefore over-fueling the float valve may well be stuck if it's been unused for a while. If your aren't precious about the mower, sometimes just banging the thing down a few steps will free it off. The other possibility is a piece of debris holding the float valve open and if it is this creating a large amount of vacuum can cause enough of a draw to pull it through. To do this though, you would need to remove the air filter and find the little arm that connects to the throttle/auto throttle. If you pull this while it is running is should rev up. If you hold the throttle open while simultaneously blocking the intake with your thumb, the increase in vacuum inside the carb will often pull any debris through. The same trick works well on larger carb engines too.

 

[robinbanks]

Could maybe whip out the sparkplug and give a good clean...perhaps even replace altogether.

Won't make any difference. If the engine is running the spark plug is doing its job

cleaned up the carburetor

What does that mean though? What did you do? What did you find?

The price of replacement small-engine carbs these days I tend not to bother overhauling them..

 

[Jonny Vee]

If it's black smoke and therefore over-fueling the float valve may well be stuck if it's been unused for a while. If your aren't precious about the mower, sometimes just banging the thing down a few steps will free it off. The other possibility is a piece of debris holding the float valve open and if it is this creating a large amount of vacuum can cause enough of a draw to pull it through. To do this though, you would need to remove the air filter and find the little arm that connects to the throttle/auto throttle. If you pull this while it is running is should rev up. If you hold the throttle open while simultaneously blocking the intake with your thumb, the increase in vacuum inside the carb will often pull any debris through. The same trick works well on larger carb engines too.

Carburetor has been cleaned and float valve was well free. Pretty weird

 

[Jonny Vee]

Won't make any difference. If the engine is running the spark plug is doing its job


What does that mean though? What did you do? What did you find?

The price of replacement small-engine carbs these days I tend not to bother overhauling them..

I haven't find anything as seemed to be pretty clean.

 

[robinbanks]

Possibly looking at something stuck or degraded then, per burnerman's suggestions. How much is a new carb?

 

[Jonny Vee]

I guess the best option is to get new carburetor. Will order one and update.

 

[Harry Bloomfield]

I guess the best option is to get new carburetor. Will order one and update.

I would be checking the air filter is not soaked in oil, and checking the oil level is correct - no higher than it's supposed to be.

 

[Jonny Vee]

I would be checking the air filter is not soaked in oil, and checking the oil level is correct - no higher than it's supposed to be.

Checked, oil filter is fine and oil level close to full but not excessive.

 

[Burnerman]

These carbs are as basic as they get......if the float valve is stuck open, fuel will run out of the carb and into the air cleaner. On the other hand, the fuel may head into the engine so give the machine the slightest tip towards the air cleaner to prevent this.
Regarding the carb, get a new one if you want but if you’ve had it to bits, ensure the main jet is tight and in its correct position, and the emulsion tube ( above the main jet) isn’t in upside down.
John