Your only going to use more fuel if you jet it bigger. If you put the stock carb and a Keihin 39 on a stock motor, the jetting is going is be the same to get the same fuel mixture. If you do mod's to it, then you will have to jet them both up so you can get more air and fuel into the motor. The advantage of a bigger carb is to get more air and fuel (if needed)into a heavy modded motor. If you don't have a lot of mod's to the motor, buying a bigger carb will be a waste of money. If you don't understand this for the seventh time, then you should let a qualified mechanic work on your atv.

 

I should let a "qualified mechanic" work on mine, your the one who's polaris is or was torn up, I think your the one who needs to learn a few things!

 

Let me put in my two cents, It doesn't matter what you do to the engine,The 39mm keihin will use more fuel,because it is a leaky carb.The pwk's leak alot,(I just seen two bran new 35mm keihins leak right from sudco)(never even opend) My 39mm pwk on my 400 scrammy has been great on power but, i have to bring alot of extra gas.The piece of junk has always leaked,and I even got a whole new one.It has a crappy float/needle and seat system which is always in need of some adjustment.The reason why I even deal with it is for two reasons,frist it is a awesome carb when it's not flooding.2nd,it's easy to jet because everyone is using it on there scrammy mods(someone always has the jetting for whatever mod you have to your 400.)
I would like to see some other carbs like lectron's or more mikiuni's used on these 400 mods,I may mess around with a lectron .

 

I guess I have gotten lucky I've had 3 pwk on race mods and never had a leaking problem. I've also got a mikuni 38mm on a trail mod and it's got a leaking problem, but I think it needs a new needle and seat. I've had a lectron on alky and sometimes it would leak, but it had a pump running to it so that's probably why it would leak!

 

Can you use a different needle and seat? I would give Keihins a call and see it they can help you out.

 

Hey Fixitmatt,
I don't know anything about that carb, but some float's have a adjustment on the float drop. Maybe the float is dropping to far and getting hung up and causing it to flooding out. Just my two cent's.

 

I think the rubber motor mounts add to the leaking as well. The 400 motor shakes and it comes out.

Ive used the bowl with no overflow and the fuel will run up the slide needle into the engine at slow speeds(ate plugs left and right) . if you set the floats high enough to stop the leaking from too much fuel on bottom the carb runs out of fuel ontop.

 

There you go WIscrambler,
I think your question has been answered. This carb doesn't sound like it would be good for you unless you are just drag racing. It sounds like your gas mileage would die with this carb leaking all the gas out. Let me know when you get together. I do a lot of riding in your neck of the wood's. Maybe we can get together and do some riding.[img]i/expressions/face-icon-small-happy.gif[/img]

 

I have tried everything new needle a seat and it still leaks. As for the float adjustment,I've tried that too.It doesn't matter it leaks.Maybe the motor shaking is some of the problem,but like I said before I've seen two Bran new pwk's leak and the quad wasn't even riden yet.(bran new banshee 421)

 

WOW, that blow's. Maybe they need to make the bowl's bigger so they can drop the float level so the gas doesn't splash out that easy. Or they can make some kind of splash shield to go into bowl. It's just a thought.