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Hi!
I have a husqvarna 2008 with an Briggs & Stratton motor model 31A6070113B1.
After half an hour the motor is decreasing and increasing the speed every second?
Next day the same issue after running half an hour.
There is a shaft on the motor wich is linked to the carburateur.
At the moment of the problem this shaft is influencing the carburateur ???
What is the function of this shaft? Or what could cause this issue?

Thanks in advance!

John

About 99% of the time when an engine with a constant speed governor surges like yours it's because of fuel starvation ( lack of fuel ) and it doesn't matter if it's a briggs or a V-!2 continental

Thats the governor shaft. the governor maintains the engine speed.
While it's probably not the cause of your problem, it's a symptom. most likely you're starving for fuel. running lean (too much air or not enough fuel). I'd replace the fuel filter first, if it has one. Also when the surging starts, loosen the fuel cap and see if it stops. If it does stop, your tank is not venting properly. No air in = no fuel out.

Hi,
Yes, first I thought the same, changed the fuel filter and also the fuel pump.
But still the problem. Also loosen the fuel cap has no effect.
Only after reducing the RPM for a while the motor gets normal but not for a long time.
Should the fuel filter be filled fully with fuel? I see only a bit fuel inside....
The fuel pump is running on vacuüm from the engine?

Thanks,

John

I’m sorry to have to post this, but if the ideas Scrub posted do not fix the problem I suggest you find a good mechanic or shop to solve the problem. Your not understanding of how an engine works could very easily cost you more money in the long run.

Btw, a fuel filter is a fuel filter or needs to be specific type for this engine?

Hi Rivets, I globally understand the working and would like to understand it more.
As it runs smoothly first half hour the problem can't be a difficult issue.
As the engine is almost 14 years old i don't want to spent to much money and when it's over ok...!
I

Then I’ll back out of this thread.

Sounds like a fuel supply problem. One thing I might check is the oil before you start it. If the fuel is draining into the oil it will run rich until the fuel evaporates from the oil as it heats up. Do a basic tune up on it, oil, fuel filter, air filter, make sure the engine has good ventilation and grass isn't packed around it, fresh fuel topped off, new plug etc.. new hoses even from the tank to the pump. retorque the head bolts.

As he surging takes a while to happen this suggests that either the fuel supply can not keep up with the demand of the engine
Or expansion is allowing an air leak to happen

The check for the latter saturate the manifold area with WD 40 from a trigger spray pack, not an aerosol can
If the engine faulters & blows white smoke you have an air leak.

For the former you have obstructions in the fuel lines, debris in the fuel tank of tank not venting to blame , even all 3 if you are really lucky

So I have work to do and hope to find the issue
Many thanks for the information and advice!

John

When it starts surging pull the fuel line from the tank loose and see if you are getting good fuel flow from the tank. I have seen fuel lines collapse when they get hot.

I would remove the fuel cap and see if it smoothens out and if it does your vent hole could be plugged. That should also help get a better flow of fuel to the inline filter.

Also check the coil, when get high temperature, probably fail. In old cars it´s the same.

Try holding the governor arm still and see what it does. If the engine dies it is a fuel problem if it keeps running and smooths out it is a governor issue.