Rejetting the carb ?

[wbilotta]

A neighbor gave me a kart with a briggs 5hp Model#130202 engine. He also gave me a couple of boxes full of spare parts. As usual, I can't leave something stock so I did some research and was amazed at the amount of aftermarket/hotrod parts available.

So yesterday I took the head off and removed some of the metal between the intake/exhaust valves to make it easier for the engine to flow. Now that I've done this can I install a thinner head gasket to bump up the compression ? I'm thinking I've lowered it a bit by removing that metal.

I installed the billet aluminum air filter adapter so I can run an aftermarket filter and now I wondering if I can rejet the carb to flow more fuel ? I would also like to remove the metal in the middle of the carb inlet where the stock air filter retaining bolt threads into. This would allow for better airflow but I'm guessing this will affect the choke. Has anyone done this and if so did you have any problems ?

 

[RanmaSal]

the material you removed from the head isn't going to lower the compression by much, seriously. If you want to raise compression and raise the CFM rate of the carb you are going to loose out on power after a certain point. There is only so much a 5HP motor can do. I wouldn't modify the intake of the carb to much as the venturi is needed. I would take out the valves and smooth out the casting there to increase flow and use a 6HP carb and shave the head slightly... maybe .020" but no more. A lot of people will say .030", and they are still correct, but .020" is more then enough and keeps the cooling property of the head the same and no worries about overheating and warping the head. If after that you need more power you should think about getting a more HP engine OR change out the valves for larger valves, change out the cam and crank, get a 8HP carb on it and balance the rotating assembly to you can turn 10,000RPM's!!!! Hey, it's been done... personally don't think I'd want something going that fast next to my HEAD, but then again I'm pretty tame

 

[jr dragster T]

Hey, it's been done... personally don't think I'd want something going that fast next to my HEAD, but then again I'm pretty tame

Thats right its been done. The Flywheel and Clutch on my Dragster is about 9" away from my head. The Cylinder head is about 4". Its all about trust in who torqued down those parts. Most of the time its me and when that engine gets going to 9500 I never worry. Do those mods that RanmaSal said and it will help.

 

[RanmaSal]

Thats right its been done. The Flywheel and Clutch on my Dragster is about 9" away from my head. The Cylinder head is about 4". Its all about trust in who torqued down those parts. Most of the time its me and when that engine gets going to 9500 I never worry. Do those mods that RanmaSal said and it will help.

Your scrodial dimentions are far greater then mine my friend... not to say I wouldn't TRY it mind you, but with the wife and the 3yrold sitting at home waiting for daddy to come make the bread for the bread I calmed WAY down and air on the side of safety. There's a country song somewhere in there...

 

[jr dragster T]

Lmao!

 

[oscaryu1]

the material you removed from the head isn't going to lower the compression by much, seriously. If you want to raise compression and raise the CFM rate of the carb you are going to loose out on power after a certain point. There is only so much a 5HP motor can do. I wouldn't modify the intake of the carb to much as the venturi is needed. I would take out the valves and smooth out the casting there to increase flow and use a 6HP carb and shave the head slightly... maybe .020" but no more. A lot of people will say .030", and they are still correct, but .020" is more then enough and keeps the cooling property of the head the same and no worries about overheating and warping the head. If after that you need more power you should think about getting a more HP engine OR change out the valves for larger valves, change out the cam and crank, get a 8HP carb on it and balance the rotating assembly to you can turn 10,000RPM's!!!! Hey, it's been done... personally don't think I'd want something going that fast next to my HEAD, but then again I'm pretty tame

6HP carburetor? Lol. I think the only main thing different there was the stroke.

No more than .030, .040 starts to restrict flow. And definitely not a 4HP "milled" head.

10,000RPM on a stock flywheel? Nahh.... Getting that cam and crank to fit would require quite a stocked up machine shop lol.