bore the carb

[youngdawg]

Does anyone know where to find info on exactly what to do step by step to bore a carb. Also, the clean-up porting can almost anyone do this? Have air tools and the patience.
One other thing. If i have the welds ground out of the stock headpipe what increase would there be from a powerbomb header?

[fmf400ex03]

bump

[boricua]

boring the carb? the carb has a venturi which is sorta like an hour glass. at the narrowest part, a vaccum is created and draws in fuel. if you bore out the carb it could change the venturi and effect how fuel is drawn in....besides that you'll need a mill (big drill press) with a special boring tool and/or a ream, depending on how big you want to go....
grinding the welds?.....probably not going to notice much of a difference....it'll reduce any hotspots and maybe (MAYBE) lower the exhaust port temp. a bit again you may not notice anything, unless the welds are just that bad.
not too sure bout the power bomb....sorry....

[nosliw]

some guys say grinding the welds in their stock header makes a big difference, some says it doesn't. you might need to fiddle with jetting.

never heard of boring a carb. heard of rifling it though, that's supposed to help pretty well.

[youngdawg]

what is rifling?

[nosliw]

Originally posted by youngdawg
what is rifling?

like on a rifle, the barrel is etched around with a spiral groove to make the bullet spin. in physics a spinning object moves faster, and with our quads spinning air means better atomization.

[youngdawg]

I'm thinking of going up to maybe 37-37.5.
Trying to keep it as a sleeper.

Already been bored and cam added.

[Crawl69]

You have to be careful when you bore it, a 400 carb is actually has an oval bore. If you take two measuments 90 degrees apart, one will be about 32 mm and the other will be 38 mm. Average the two and you'll get 35.5 mm. I bored my stock carb in a lathe. Just remember if you do it yourself, the brass tube that squirts gas from the accelerator pump will have to be pressed out. It's a real pain in the *****, and after several choice words you might get it out without breaking it. I used a lathe because all of the mills at work were set up wi something. Just be really careful and remember that the max you can take it out to is 38 mm.

[JOEX]

Originally posted by Crawl69
You have to be careful when you bore it, a 400 carb is actually has an oval bore. If you take two measuments 90 degrees apart, one will be about 32 mm and the other will be 38 mm. Average the two and you'll get 35.5 mm. I bored my stock carb in a lathe. Just remember if you do it yourself, the brass tube that squirts gas from the accelerator pump will have to be pressed out. It's a real pain in the *****, and after several choice words you might get it out without breaking it. I used a lathe because all of the mills at work were set up wi something. Just be really careful and remember that the max you can take it out to is 38 mm.
So when it's bored to 38mm does that mean it's 38mm round or 38mm oval/average?

[Crawl69]

round