Older B&S engine running irratically

[Mechanos]

Not really tractor related... but I have an older Briggs & Stratton (probably 25 to 30 years old) horizontal shaft, gear drive engine off on an old retired walk-behind snow thrower. The engine still runs like a champ under load and really hasn't seen that many hours of operation considering it's age. When the engine is not under load, it will not run at a constant speed... it revs up, then the governor throttles it down, then revs back up and the cycle repeats. It repeats this cycle every second or two.

It really wasn't that big of a deal on the snow thrower as the amount of time the engine was just idling was minimal. I'm wanting to use this engine with a two stage hydraulic pump to power a log splitter. Listening to the engine bounce off the governor for any extended period of time is quite maddening.

Can anyone familiar with these old gas engines offer any suggestions as to what is causing it run irratically and what I can do to fix it?

 

[whistlepig]

Not really tractor related... but I have an older Briggs & Stratton (probably 25 to 30 years old) horizontal shaft, gear drive engine off on an old retired walk-behind snow thrower. The engine still runs like a champ under load and really hasn't seen that many hours of operation considering it's age. When the engine is not under load, it will not run at a constant speed... it revs up, then the governor throttles it down, then revs back up and the cycle repeats. It repeats this cycle every second or two.

It really wasn't that big of a deal on the snow thrower as the amount of time the engine was just idling was minimal. I'm wanting to use this engine with a two stage hydraulic pump to power a log splitter. Listening to the engine bounce off the governor for any extended period of time is quite maddening.

Can anyone familiar with these old gas engines offer any suggestions as to what is causing it run irratically and what I can do to fix it?

This is called "hunting" on a motor. In my experience the first cause was the carb being out of adjustment. Second was shellac in the carb. Restricted air intake can cause this also. Fuel or air is being restricted. Last fix is the governor.

 

[Mechanos]

Thanks. I'm positive that there is no air restriction. I'll start by takng the carb off and soak it, then clean it real good and blow out all the little passages. I'll see if that helps any before going further into it.

 

[bcp]

If it has several holes where the governor connects to the throttle, it may be in the wrong hole.

Bruce

 

[schmism]

hunting or surging is gennerally a sign of a lean condition.

if a carb tweek of the needles doesnt fix it your going to need a rebuild to clean out the ports etc.

 

[jinman]

I think you will find on those old Briggs that surging at idle is normally related to the governor spring tension on the carb butterfly. The spring has to have the correct tension. Do you know if the governor is operated by the crankcase or an air vane? If it is a crankcase governor, you may be able to loosen the clamp on the shaft were the lever arm attaches. There will be a slot in the shaft for hold it and change the angle of the lever a tiny amount. If it's an air vane type governor, you may be able to set the spring length on the carb butterfly by bending it in a slightly different position.

EDIT: If you are interested in learning how to adjust the two types of governors, this B&S tech link may be of help.

 

[ToadHill]

Before you take the carb off check one thing. Does it run better with the choke on part way? If so take some oil and drip it around the intake gasket, if you get blue smoke than the gasket is bad and it is causing a lean condition.

I've found this often happens with older B&S motors.

 

[Travelover]

I'd agree with the carburetor being the culprit. Check for bad gaskets, then disassemble it, soak it in carb cleaner and reassemble.

Make sure that you unscrew and remove the high speed jet tube before you split the carburetor

 

[Snaker]

I've fixed several engines with this problem by bending the float to float needle clip for a tight fit. I believe that ethylnal causes the needle to stick and the float has to pull it down.

 

[Soundguy]

yep.. hunting can be fuel deliver issues.. plug, obstruction, varnish, lean vacume leak.. etc..

soundguy