If a person puts a bigger carb (say upgrading from a 39mm carb to a 42mm carb) on their quad.

Would he have to have a different size (smaller) jet since it is a bigger carb? or does the jetting have to be the same regardless of the size carburetor installed.

 

It's all about keeping the proper air to fuel ratio. A larger carb will let a little more air into the engine compared to a smaller carb, so the jetting would have to be increased accordingly. This is assuming that the bigger carb is properly matched to the machine though. Just going to a bigger carb can actually hurt performance if it's going onto a machine that actually doesn't need a bigger one. Heck, the edelbrock carb's bore for the warrior is actually a little big smaller than the stock one, and it still adds a bunch of power. The reason is that there is more air velocity in the carb, so the fuel atomizes better and burns more thoroughly.

 

ya but would a bigger size carb have the same size jets? or would it be a lot of guess work to get the jetting right on again.

 

There's a lot of mathematics and physics involved in it. Going only from a small bore to a slightly larger one doesn't make much of a difference at all in the jetting. What makes a bigger difference is the actual design of the carb itself. So it depends on what you're replacing with what. Give some more specifics.

 

keihin PTG23 to a KEIHIN FCR-MX 37mm

it says its for 250-375CC

http://www.keihin-us.com/am/products/fcrmx.php

 

Do you know if it'll even be a straight swap between that and the stock carb? The size of the necks, the lengths, and stuff like that aren't a universal thing. I'm not a big fan of running carbs that weren't specifically designed for the machine, because there can be an ***-ton of work involved between fabrication and tuning.

 

i wasnt really getting serious about swapping a bigger carb into the quad, but if it was ever necessary, or even beneficial, i was wondering how hard it would be.

 

a 37mm in a ds250 would be way too big. That little ds doesn't breath enough to benefit, it would actually loose power and efficiency from it. The only way that any 250 would benefit if it was one of the beefier 250's to begin with, like maybe a mojave, and then only after that's been cammed, high compression piston, exhaust, etc. There is no machine that I know of that when stock, would actually benefit from a larger carb. Maybe a better designed carb, but not just a larger one.

 

When guys go to the TM45mm carb from the bsr 42mm mikuni on the ds650 they use smaller jets but use more gas [img]i/expressions/face-icon-small-confused.gif[/img]

 

$20 says it IS better designed too, though, so it just MIGHT benefit.

i dont know, maybe in the 2 years if a bore kit or stroker kit comes out, i'ld go for it, unless i have plenty of $$ to upgrade, and high comp, then i would go bigger