Champion Lawnmower Poor Running.

[Brownlie1985]

I have a champion mower and its been great for years. Recently its begun to run poorly. It will not maintain a constant RPM. revving and hunting.

 

I think its do do with the springs on the carb as pictured. Any help or advice would be greatly appreciated.

 

Mike

[PeteB]

Sounds like the govenor springs/set up has become too active.

[GardenKit]

Common problem on the B&S Sprint engine. The carburettor will need a good clean out and the diaphragms will need replacement. A simple job, I do 100's every year.

2 bolts hold the tank and carb to the engine. Once the tank is on the bench the 5 screws can be undone and the carb removed. Replace the diaphragms and refit. All will be well.

[Brownlie1985]

Sounds like the govenor springs/set up has become too active.

 

Yep spot on.

 

Springs are loose. I've ordered up new springs.

 

When engine is running the governor arm is bouncing about as it has no tension on springs.

 

 

 

 

 

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[GardenKit]

Yep spot on.

 

Springs are loose. I've ordered up new springs.

 

When engine is running the governor arm is bouncing about as it has no tension on springs.

 

 

 

 

 

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Those springs are fine, it will be the carb causing the problem, the governor is merely trying to compensate.

[Rich2484]

Im with gardenkit on this one I'm afraid. The springs don't tend to do this unless they have been pulled about. They are only weak springs to begin with.

 

The carb will be the issue.

[Brownlie1985]

Im with gardenkit on this one I'm afraid. The springs don't tend to do this unless they have been pulled about. They are only weak springs to begin with.

 

The carb will be the issue.

 

No matter where the throttle is the governor spring is loose. A tiny bit of tension on the spring and it holds constant rpm.

 

 

 

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[Rich2484]

It will. That's how it works, small tension, the guv. Is run on engine, the engine speed is ultimately controlled by the carb and fuel/air intake.

 

Gardenkit will explain better, or spud as I'm crap at writing down explanations.

[Quercus-90]

Common problem on the B&S Sprint engine. The carburettor will need a good clean out and the diaphragms will need replacement. A simple job, I do 100's every year.

2 bolts hold the tank and carb to the engine. Once the tank is on the bench the 5 screws can be undone and the carb removed. Replace the diaphragms and refit. All will be well.

 

Definitely the carb. Don't forget to flush the tank, and bin your fuel! It's probably manky!

 

Think a carb, in diaphragms is circa £30 trade?

 

 

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[GardenKit]

The trouble with holding the throttle is that it induces a false diagnosis. Yes the engine will run smoothly using whatever fuel is available, but the air mixture will be wrong.

 

The problem WILL be the carb. The springs do not go weak. They can be stretched by damage but that merely results in a low engine speed.(the smaller spring does balance the governor slightly, and this one is prone to breaking)

 

The governor works by airflow from the flywheel acting on a vane. The higher the revs, the more pressure on the vane.

 

As the revs increase the vane pulls on the the throttle butterfly via a short link and tries to shut the engine revs down. The throttle spring pulls the other way and overcomes some of the wind force, thereby opening the butterfly and increasing the revs.

 

The engine revs are stable at any point that the wind force and spring tension are in equilibrium.

 

As the revs drop under load so does the wind force, so the spring force allows the butterfly to open, feeding in more fuel which increases the revs again, as well as the wind force which counteracts the spring and shuts the butterfly, lowering the revs. And so on,and on.

 

Too little fuel from a contaminated carb will cause the carb to hunt.

 

A carb diaphragm set is £2.25 plus vat or a complete carb is only £14.30 plus vat

 

Some pics of the diaphragms, these were damaged by stale fuel. One reason I use Aspen.

 

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