400ex carb tuning v.13147234

[not2hi]

Just bought a stock 400ex carb to throw on our 300ex...148 main 38 pilot 2-1/2 turns on the bottom screw...

FYI, wiseco 11:1 .040 over, webcam, titanium valves and springs, FMF megamax system, no limit CDI, Uni fiter and holed airbox with lid

when we first put it on, it fired right up, ran a minute or two then died...wouldn't restart. Yesteday had the plug out for a while, popped it back in, fired right up and then died.

after further review, its fouling the plug, and gas is even the airbox, so its flooding...

guy I bought the carb from was using in his 300 an said it worked fine.

So i'm not even sure where to start - most jetting instructions start at idle, whereas i can't even get this one going for any length of time.

So I'm looking for advice on what to do first...

also, I'm going to buy some main and pilot jets for tuning, but not sure what sizes to buy (couple sizes smaller and couple sizes bigger for both?) and i guess a bunch of new plugs.

thanks
-mark-

[BEAVER.989]

First thing you'll need is a smaller pilot to get it to idle. I'd start two sizes smaller than where you're at.

[not2hi]

cool, thanks...I'll buy 2-3 sizes smaller and maybe one bigger

jets-r-us is a good place to buy?

[BEAVER.989]

Jets R Us is a great place to buy. Save your money on the larger jets, you don't need 'em.

[not2hi]

looks like the smallest pilot is a 35?

[BEAVER.989]

From what I can tell, you are correct. It seems strange to me that being off one size on your pilot would be causing so many problems for you. I think you may have other issues.

[not2hi]

i'm going to order rebuild kit first, certainly can't hurt...wondering if there's a float issue there as well

i see alot of peeps running 42 pilots in their 300exs with the 400ex carbs.

i agree, i wouldn't think the 35-38 would make that much difference either.