Well there are several things here. First while there are two spark plug leads, there is only one coil. I don't see where you cleaned the carb float bowl. Remove the hex head plug on the lower right side (when facing the carb) be aware that gas and perhaps crape will run out. IF this doesn't help, you may need to remove the top of the carb and clean the bowl. Caution: the gasket must come off with the top, this gasket will be very hard to find short of an overhaul kit if damaged.

Before removing the carb top, you may want to check compression on erratic cylinder. It is possible a valve is sticking OR a valve seat is hopping out. Also, there is an adjusting screw just below the air cleaner sticking straight out at you. Turn the screw 1/8 turn counter clockwise.

Walt Conner

Thanks for the advice Walt.

I removed the carb last night, disassembled and have been soaking it in carb cleaner. I got a carb overhaul kit and will be putting the carb back on tonight.

I will check compression on both cylinders.

I'm not sure what adjusting screw you're referring to. I'm assuming you're referring to an adjusting screw on the carb. The only screws on the front of the carb that could be adjusted are the Idle Speed screw and the Idle Mixture Jet screw. The Idle Speed doesn't seem to be my problem and according to the Briggs and Stratton manual for this engine, the Idle Mixture Jet screw is nonadjustable.

So I put the carb back together with the new parts from the rebuild kit and put everything back together on the mower. Started up fine and ran steady at full throttle. Tested low and medium throttle and seemed to run good. So I decided to take 20 mins to mow the front lawn and see how it ran. Everything seemed good while I was mowing, so when I got done I lowered the throttle to about half speed and it started surging again. Brought it in the shed, checked for good spark on both cylinders and ran engine on each cylinder separately. Fired it back up with both cylinders and ran fine at all throttle levels. Mowed the back lawn the next morning and no problems at all. Ran it at low, medium and high after I got done mowing and no surging.

I am still a little concerned though because it did surge after the first mowing when i put it back together. Do you think my problem is fixed or is there something else I can check?

The funny thing is my friends mower does the same surging when he runs at half throttle, but it runs fine at full throttle. He has a different model, but its a Briggs and has the same basic configuration. Is there a known problem that will cause these engines to surge when not at full throttle?

You are esentially seeing the effects of the governor trying to find a "sweet spot" in lower RPM range that it is not able to find when the engine has no load on it.
The surging is actually quite common to the opposed twins and is not really a "problem", it's just a characteristic of an engine that was built to do some work at full open throttle and full fuel flow through the main jet. At low RPM and no load, the governor has to hunt for satisfaction
that it can't seem to find.