Hey guys, I dug up an old push lawn mower from in my garage for my sister. It probably hasn't been run in 5 years so I took it all apart and cleaned it a bit. I changed the spark plug and put a bottle of carburator cleaner through the gas tank. Now it seems as if its not running at its full potential. For example it bogs down a bit in slightly tall grass. Is there a govener on these? I believe its a 3.5hp briggs and straton motor. Any ideas why it doesnt seem to run as fast as it should? Also can you use a grinder to sharpen the blades? Thanks

 

As a rebuilder of dozens of Briggs and Stratton single cylinder engines, I feel I can answer this. The governors are usually air vanes that are blown by the flywheel, and are conneted to the throttle assembly. On 3.5 horse engines this is hidden behind the cowling that holds the rope starter. You can check to see if it is connected or, more common, if the line is rubbing on the cowling. Remove the air filter and see if the choke connection is working properly.

It is safe to grind the blade, just use a blade balancer or it will be uneven.

The throttle assembly on these, the 3.5 horses especially, are the most complicated things on the engine. I could probably reassemble one of these blind folded, as I once fixed them in school competitons, so if the throttle assembly is fine get back to me for more ideas. It may be time to check compression or the carburetor or something.

 

Yes it has a governer its a air controled governer.It sits under the cover its hard to discrip but its a plastic piece that swivals connecting to the carb.Is it a 3 hp or a 5 hp if its a 5 then Jegs sells racing set ups for the 5 .As to grinding the blades yes but use a bench and balince the blade.How to balance its easy take blade bolt hole use finger or other object and get it to balence.

 

If you've got a grinder and a vise you can balance the blade prettty easy. Put the handle of a screwdriver in the vise, with the end of it stick out to the side. Put the blade on the screw driver horizontally, and see if it turns one way or the other. If it doesn't turn, you've got it balanced. You can take a little bit off the side that falls down if it's not.

 

Being that it had been sitting for several years, my guess that you have a restriction in the carburator. Just running carb cleaner through the gas tank will not get the job done. I would order a carb kit and disassemble the carb and give it a complete cleaning. A carb kit for the 3.5 hp Briggs will probably be less than $15.00. I bet that will solve your power problems.

 

Give me the model and type numbers off the shroud and I can get you a part number for the carb kit if you want.

 

I'm betting the valve seats still have some carbon keeping them from closing all the way. Did you remove the head and use low grit paper or compound on the valves and seats? Just my $.02. Nat

 

What exactly does a carb kit do? No I did not use sand paper to clean the valve seats. There was some black soot on the the valves and around there but I cleaned them. I guess I should get a carb kit but I don't really understand what all that does. I'll look today and see if I can get it to work better. Thanks

 

A carb kit replaces all the gaskets and orings inside the carburator.

If you havent already cleaned the carb (take apart and clean well) then do so.

The 3.5hp pushers arent realy that powerfull as it is. I bog down mine all the time in thick grass and its brand new.

You could bomb it and hook up a manual trottle control and kick up the revs a bit but thats dangerous if it somehow gets away from you. You could also throw the weak oil dipper and blow the motor.

 

Something else to check on a motor that does not rev up properly is a partially blocked muffler. Not that common a problem on the 4 strokes such as the B&S but can be a problem on 2 strokes. If this machine has sat for a while is it possible that mud wasps have built a nest inside the muffler?
A quick and dirty fix for dried varnish inside a carb is to drain it and then fill just the float chamber with a mixture of 50/50 lacquer thinners and regular gas. Start the engine and run that thru then try it with just straight gas. WARNING: Do not let the thinners/gas mixture sit for more than a few minutes in the carb as it can damage any rubber in the carb. This is why it is necessary to quickly go back to 100% regular gas. There are commercial products that do the same thing and are not as harsh.

 

This is great. BOMBing lawin mowers Kind of off topic, but we had a 3.5 horse briggs and stratton a couple years ago and I rigged up a straight pipe for it Dad never really noticed until he had to use it, then he welded a $2 muffler on it

 

I reccomend a Scotty II to keep those EGT's down and keep the COOOOoooooooOOOOooooo0000000l air flowing.

Maybe some bigger injectors??

TWins would be a nice touch. Nitrous or propane should get her buzzing again too.

 

Cumminsdude, I assume you've already checked all the throttle linkages between the carb and governor to see if they're connected and aren't rubbing on the cover?
Depending on the carb. type, it might be easier to buy a new one than rebuild. I didn't know you could rebuild the one pieces...
Another possibility would be a sheared flywheel key. Little piece of aluminum on the flywheel that breaks in half if the engine stops quickly, so if you hit an object the flywheel's inertia doesn't break the connecting rod. These can lead to problems if they are damaged.

 

Ok thanks for all of the ideas. I think I've come to realize that the 3.5 hp just isnt what I thought it was. I will clean the carb one more time when I get time. I'm working on a weedeater now! Thanks all

 

do yourself a favor..never rig up a nitrous shot to a push mower if you value your neighbors windows or pets.. AND the little motor.. ....on a lighter note has anyone ever had rope burn from one? ouch..