Up and down. Up and down

Briggs 128M02 0945 F1

Original Carb was very dirty, so I put a new one on it. It fires right up, usually first pull. But revs up and down. Sprayed soapy water around where the carb mounts, and nothing changes. Took the cover off and didn't find any cracks in the intake.
So I cleaned out the original carb, and still getting the same revving up and down.

The only thing different is the throttle/governor spring is different. The original one was rusted and broken. So I put one on that's a little different, but seemed to have about the same tension on it. It's a little longer so I had to slide it over where the original one hooked to (front of the engine on the front plate) and hook it below. I tried more & less tension, but it makes no difference. Less tension, slower idle, it doesn't rev as much. But still revs.

The plug is good. Compression is about 65 to 70 with fresh oil. New air filter.


Any suggestions?

Since you changed the Gov. spring with a non O.E.M. spring, that's probably the problem.....Gov springs are not all the same and are very sensitive. Check stuck carb choke also!

Start the engine the put your finger on the governor and manually increase the throttle slowly till the engine is doing full revs
Listen for the engine missing lean.
If it does then make up an altrnative fuel tank.
IF you are going to succeed in this business a secondary fuel supply is an essential tool and there are plenty of old tanks around.
Most workshops will have one on a stand or hanging from a rafter .
I use an old Victa pro walk behind tank as it holds a gallon and has a combined tap & filter in it.
Before that is was a Tecumseh tank for the same reason.
It does not need to be big, one out of cheap Chinese monkey bike will do just so long as it has a 1/4" fuel tap and holds about 1 pint.

Hook up alternative tank and the problem goes away = fuel supply problem.
Drop the tank to floor level and problem comes back = fuel pump problem.

Takes all of two minutes saves many hours

bertsmobile1 said:

Start the engine the put your finger on the governor and manually increase the throttle slowly till the engine is doing full revs
Listen for the engine missing lean.
If it does then make up an altrnative fuel tank.
IF you are going to succeed in this business a secondary fuel supply is an essential tool and there are plenty of old tanks around.
Most workshops will have one on a stand or hanging from a rafter .
I use an old Victa pro walk behind tank as it holds a gallon and has a combined tap & filter in it.
Before that is was a Tecumseh tank for the same reason.
It does not need to be big, one out of cheap Chinese monkey bike will do just so long as it has a 1/4" fuel tap and holds about 1 pint.

Hook up alternative tank and the problem goes away = fuel supply problem.
Drop the tank to floor level and problem comes back = fuel pump problem.

Takes all of two minutes saves many hours

Click to expand...

Thanks for that. An extra tank is something I used to have at my last shop. Fresh gas in an old tank doesn't mean fresh gas going into the tank. When I took the bowl off, I found something cloudy in it. So I drained some into an empty coke bottle and wow. it was nasty, And even had water in it.

But I think I've found the problem. The spring I was using was just not stiff enough. I found a stiffer on put it on and problem solved.

If it is too stiff the governor won't be able to respond to changing load conditions.

The governor spring is part of the engine so use the engine numbers and order the correct one they are only a few $$ .

You don't want it coming back with the customer complaining you have turned their mower into a unich

bertsmobile1 said:

The governor spring is part of the engine so use the engine numbers and order the correct one they are only a few $$ .

You don't want it coming back with the customer complaining you have turned their mower into a unich

Click to expand...

I seriously have to get me a tachometer. When I get a little extra money for tools, I always forget that.

BTW, I got my fuel tank set up in the shop. I built a little stand to carry it out doors with me.