Originally Posted By: ac_tc
the silencer (exhaust) is usually a ridiculuis piece of trash!
Open it up and let it breath, i once made a pipe and just let
it exhaust under the deck...didnt sound to bad.
also intakes are relly bad enginered, use your dremel!
Milling the head -ok but watch for valve clearance!
Yeah, I used a 3.5hp Briggs mower with 3/4" straight pipes for a few years, the neighbors loved it.
Cheap aluminum lawnmower engines usually have a lot of casting flash or other mismatch in the intake area, a dremel can really help. Just like working on a 350 chevy, but smaller...
I would also think if you wanted a less restrictive air filter, but not quite so much work as that cool oil bath filter, you could use a go kart filter that will let in more dirt, but mount it on the top of the recoil housing where there is less lawnmower dust.
Oh, and current production small lawnmower motors/carbs are GARBAGE for power (torque) thanks to our friends at the EPA. If your lawnmower has the newer non adjustable type carb, you might be able to find a bolt on replacement that is adjustable from an older mower. (ebay!) More power and easier to start.
I have a Horizontal Briggs Intek engine on a generator I built that started as a 5.5hp 190cc. I stroked it to 206cc, put in a go kart rod, replaced the plastic cam with an iron one, and found an older adjustable type carb, increased the CR a bit. It's putting out at least 8-10hp now.