racing gokart

[j2004jeepwrangler]

Hey guys I could use alittle insite on porting a 5hp Briggs flat head. I ported the intake and exhaust, but Im wanting to put a D shape in the exhaust will jb weld hold up?

[MX Quad Dad]

would this be a OHV engine?

Im not even sure if they make a 5HP OHV. I had the good fortune to take a few laps on a cart with the old flat heads 5hp. the guy who let me take the laps was a racer and built his own engines. every time I hit the throttle I would look over at that little briggs and had a hard time beliving it had that much power. I talked to him for a while and he told me a lot of what he had done to it. unfortunatly it has been a while and can't remember much. I know he said he had made a jig and ground the heel of the cam to get more lift and didn't use a keyway in he flyweel just valve grinding compound.

He could have been feeding me a line of bull but, he had retired from racing and it was just a club that just spent a weekend a mounth at members who had a track in thier back yard. I allways think I will look him up and build a couple carts.

Oh yeah... no knolage if the jb will hold up

[j2004jeepwrangler]

Yes its a flat head 5hp. Ill upload some pictures of the port work and jb weld. I shaved the eye brows and milled the head. Im putting a 6hp intake valve in it. Its 2 mm bigger, and im going to try a 22 mm round slide carb. Im working on a 3 stage exhaust. I don't have the billet rod or flywheel, so it wont be reved passed 5, 000 rpm. I built a ho da clone 5.5 hp put bigger valves and heavier springs and it just rips for a gokart. It will even bust the tire yes one will pill on black top for a good 5 feet.

[MX Quad Dad]

before my son started racing MX, he had come home from a fair with the rules for garden tractor pulling. my fatherinlaw had an old 12HP simplicitiy that he had picked up for scrap. the rules at that time said I couldn't swap to a side draft carb. I am a bit of a pac-rat aand I had a lot of briggs parts plus a box full of updraft carbs. anyway between the parts swapping and a lot of grinding in the intake and exhaust (the exhaust had female pipe thread which I groud completly out plus a bit more). Had a a friend who owned a machine shop put his spindle tach on the crank and he had me run it up three times before he finally said I had it turnning 6500. and that was with a stock crank and rod that I modified slightly in hopes of it channel more oil to the rod jurnal. of coarse it only hit those rpm's for a short time. but we ran it for two seasons and he hit a few pulls after he started running MX.

Should allway know wha type of compiition you have before you get your hopes up. I thought it was a bunch of kids, but there were guys there that had been pulling garden tractors for years and those built Kohlers are hard to beat we did start to get thier attention tho.

[j2004jeepwrangler]

Well I got it ported I actualy put a + two mm valve in it and ported the intake and used the jb weld to help flow. I put a D shape in the exhaust . To took the cam put it in a vise heated up and twisted it by about 2 dagrees, had my dad weld the cam wich took FOR EVER to file down. But finally got it together and started Im pretty sure my right arm its twice as big as my left. But it runs great. It has a mean idle to it pretty thumpy. And revs like no other. Dtill have to mount it to the kart and test it.

[MX Quad Dad]

QUOTE (j2004jeepwrangler @ May 20 2013, 01:55 AM) <{POST_SNAPBACK}>

had my dad weld the cam wich took FOR EVER to file down.

thats why the guy I talked to, ground the heel of the cam, which I believed he would have had to weld up the tappet where it touches the valve to take up the clearance.

funny, people stil call them a 5HP briggs. I really wonder how much HP you can get out of them on gasoline and alcohol