jetting..

[Fleshwound]

what size main jet should i run with just a 440 kit and wb slip on?
and what size pilot jet do i go to after removing the choke and dremeling the sides??

[Fleshwound]

bump

[jerry-89-250R]

no one can tell you the exact main, there's too many thing's too consider, good starting point 160 main, ride it and go from there, i would try needle raising the needle too 2nd position from top also, but that's just a starting point, on pilot jet, up 1 or 2 sizes should be fine

[Fleshwound]

yeah i figured that but its just that i am rebuilding it over the winter and just wanted to get an idea of what to start with at the beginning of the race season...thanx

[flying400ex]

What is the stock main jet size? Isn't it 155?

[intruder]

The stock main is 148. The jets I have in my sons 440 with port and polish are: without airbox lid 45 pilot and 190 main with the clip all the way at the bottom on the dynojet needle. With the lid on, 42 pilot and 170 main and move the clip up 1 position on the needle. But there are alot of factors to consider air filter, altitude, temp. Its more of a trial and error type thing. But you want to be rich if anything. I was told wind it out in third gear and pull the engine kill check the plug it should be like a clay brown color.

[Desert Rat]

If you buy a dino jet kit it has good instructions that includes variable in the tables like altitude. It also has a new and different needle that works better than the stock one. It has a variety of main jets you can use for different riding conditions. Also, if you do the plug check you need to warm up the engine and do it with a new plug each time or a used one that has been sanblasted clean to get a good reading. To check the main jet run it all out in high gear for fifty yards or more and kill the engine and pull in the clutch at full throttle to do the plug check. Do the same thing at half throttle to check the needle position. If it starts and idles good you don't have to mess with the pilot jet. The porcelain tip on the plug shoud be a tan color. White=too lean. Black=too rich. Some people advocate just increasing the main jet size until the engine starts to blubber and then drop back one size. You won't be running lean for sure if you do it this way. I run a stock pilot jet, 165 main, and the needle clip on the second from bottom position at 4,000 ft. elevation on the quad in my signature.

Pilot jet size affects starting and idle.
Needle position affects mid range.
Main jet size affects top end.

Very little overlap in the affect of one on the other.

[Scott400EX]

ok heres what i have. 42 pilot, needle clip 3 from the top, and a 165 main. and the pilot screw a little over 2 turns out.

Mine smells rich at idle is my pilot too big for the mods i have listed below. It starts without needing to punch the throttle at all. and idles but tends to need the throttle held a little till it warms up or it will cut off. the plug was dark brown but i havent checked it in a while.

what would you all try in this case? I have a 40 and the stock 38 pilot too.

[400exBro]

i am running a 160 main, 3rd notch on the needle, and a 42 pilot jet with a wb e-seris 12 discs, 4- 7/8" holes, and a K&N air filter...

And the elavtion change between me and you aint that much, so i think you should start at a 170 main and work from there, also what comp piston are you running??

lata
Bro

[Fleshwound]

i dont even know what piston is in the engine...
the guy that i bought it from had it totally done up then parted it out ...im not sure whats in the engine.....
i think os valves and maybe some porting....it seems faster than just a 440 meh....oh yeah i am running a k&n with an outerwear and no lid