Briggs Stratton Quantum engine surging

[alex_at]

Hi, I have an old lawn mower that does the job just fine, except the briggs stratton quantum engine is surging. I disassembled the unit to find that black mixture/speed governor on top of the carburator is constantly moving when the engine is running. If I block it so it can't move the mower runs fine, no surging. See picture attached How to fix this? Is the spring loose, a screw loose or do I need a new carb? Thanks, Alex

 

[ZebRuaj]

Autochoke? Spring is doing its job. You probably just need to clean out the carb.

 

[samven]

The governor is hunting. Might be a weak spring or linkage is dirty and need clean/lube. If the spring is weak it is constantly overshooting, falling back then repeat. If things are dirty it binds then over corrects then drops back and repeats. Make sure you note what hole the spring is in if it has adjustments. You dont want to start playing with those you will only make it imposable to figure out. Use a soft tooth brush and brake cleaner to get all the grease and dirt off then just a touch of oil and retest before you buy a new spring.

 

[JohnG]

Is this under load or at idle? If it's at idle, without load, try reducing the idle speed a little. You are definitely getting "into" the governor with the surge. I've seen it a lot. Usually putting a load on the engine smooths this action out, but not always. Pressure washers seem to be the biggest offenders.

 

[alex_at]

no issues at idle, but as soon as I set the speed to max it starts ..... carb is getting a clean tomorrow maybe, I will note what setting the sping is. If nothing helps, a new carb is only 25$ shipped.

 

[WhyMe]

surging in my experience means it running lean. Clean the carb orifices and see what happens

 

[jakewells]

Either a dirty carb or a worn throttle shaft.

 

[rocky37]

The mower is surging/hunting because the carb is dirty. The main jet needs to be cleaned. You may be able to clean the carb without removing the carb. There is a main jet at the bottom of the carb that retains the fuel bowl. Take that bolt/jet off and spray carb cleaner through it. This may be enough to fix the issue. The reason why the engine is surging is because the carb is causing a lean condition and this causes the engine to slow down. After slowing down, the condition is back to normal and the governor will increase engine speed and then the condition starts all over again...surging.

 

[Brybo86]

i had a mower with that same engine after starting it one spring it was surging try holding the spring/throttle in a fixed position, if it still surges then your carb is dirty if holding it still (try holding it still at low and high RPM) stops the surging then you just need to buy a new governor spring i bought a new spring and the mower is still running great to this day

 

[mk378]

The part that is moving is the throttle plate. With no load, the engine should run steady and slow if you hold it against the stop on the slow end. If it stalls out when you do that, the low speed circuit in the carb is clogged, and that will cause the rpm to surge up and down with no load. Basically the engine stops firing completely instead of going slow-- as it slows down too much the governor pulls the throttle toward wide open, and then it starts firing again and revs up too much. This repeats as the surging pattern. Some versions do not have a low speed circuit at all and they are prone to surge anyway.

 

[Convert]

Clean the carburetor, the emulsifier tube has for tiny little holes in it towards the threaded end ,clean those holes out and everything should be fine .had the same problem with my snowblower with a Briggs engine. TOMB

 

[Lubener]

Carb needing cleaning, rebuilding or replacement.

 

[eljefino]

Originally Posted by WhyMe

surging in my experience means it running lean. Clean the carb orifices and see what happens

+2

 

[motor_oil_madman]

It will suge if you run it without the air cleaner on just fyi. Had that happen once while I was testing my carb cleaning job. Then it stopped once I put it back on.

 

[alex_at]

so update: Took the carb off and opened it up. It was pretty clean, I was expecting varnish and gunk. I didn't have carb cleaner on hand, shops are closed due to corona. But brake cleaner and my portable mini compressor did the job. Now it runs fine. No surging, just nicely running. After reassembly I managed to completely flood the engine, i was priming too much. But got it running. Changed the 3 or 4 yr old 5W-40 A3/B4 to Petro Canada Duron XL 15W-40. Discovered that the cutting knife was pretty loose - so fixed that too. Now the mowing season can begin. Thanks everyone for your help.

 

[thastinger]

It is running lean, you either have an air leak in the intake track (like where the manifold attaches to the cylinder hear or on the engine side of the carb) or your jets are clogged in the carb, thus not delivering enough fuel. When the engine is lean, it tries to run at a higher RPM than 3600. You governor is doing its job fine it seems.

 

[dwendt44]

The governor arm could be sticky as well. Clean and dry lubricate the pivot point. My 2¢