Motormind, that doesn't always work quite like that. Yes, when forcing air through a smaller orifice, it does move faster. But air being pulled(suction) can only go as fast as it is pulled, and is limited by the smallest point. In other words, you can't "port" the carb and expect increased performance if the head isn't ported.
Of course, a turbocharger would change that. Then, you are forcing the air/fuel, and suction has nothing to do with it anymore.
A turbocharger is a device that forces air into the carb at a substantial rate. It is driven by a device that the exhaust goes through. FYI, a supercharger is essentially the same, except it is belt driven. I don't think anyone makes either for these types of motor, although I seem to remember a month or so ago someone posted one that would fit.
Try this, but be gentile. With compressed air, take off the air filter of your motor. With a spray fitting, shoot a quick burst of air into the carb and see what happens! But doing this bypasses the governor, so don't hold it on for long. Just a short burst.
cut the ez spin lobe off the camshaft so that the intake valve closes all the way on the compression stroke. You will see an improvement in the low end power and the engine will idle lower . Or find a cam from a 1960 or older 3hp briggs.
well heres the good thing.... the one 3 horse im rebuilding is from the 50's. so i beleive the cam would be good. this project and all my projects have been put on hold for a year due to down sizing of my house. but, now things are up and im ready to pick up were i left off! im gonna post some pics of the build here in a few days, the moter i used is the one i posted pics of in the post earlier and is my avatar photo as well!!!
OK, that's a good start. If that is the original engine cover for that block then it a 1958 to 1960. the ez spin started in 61. Are you sure that it is a 3hp ? that is an early style up draft carb off a cast iron briggs and not original to the engine but it will work fine. That's a hard to find carb so don't scrap it. For your build, keep it simple and just do some basic mods.
1, stress relieve the rod-polish up the casting seam
2,porting, don't go crazy just smooth up the casting burrs and round the top edge of the port to smooth up the turn into the valve also clean and lap the valves
3,cut eyebrows and make a rounded ramp into the cylinder
4 mill the head
5 header or drill out a stock briggs round muffler
6 low restriction air filter
any stock briggs carb will work fine for this.
these simple mods don't cost anything to do and will help improve the performance. I just built a couple 3hp briggs engines like this and saw an improvement in the mid range power.
then just get it running good first, your first mods should be a low restriction air filter and a header which can be just a legnth of water pipe. Later you can add a milled head to raise the compression. You can get by without changing any thing else inside the engine or add them one at a time once you research it and know what you need to do.
Im looking fornhelp beefing up annoldn3hp flathead. Its a kawasaki copy of a briggs. Im using this engine as it is the largest i can fit in my frame. Im looking for anything i can do to give it a bit more. I dont mind the work and i understand a 5 hp is easier to get parts for but like i said this is the biggest block i can fit.