Hesitation When Hitting The Throttle

[countypark]

Can anyone tell me if I the Pilot Jet size has anything to do with my quad hesitating when I have it at idle then punch it to WOT?

If I ease it from idle to WOT it responds ok.

I am running a 400ex carb on a 330EX with a TC cross country cam. 11.5:1 compression

I adjusted my needle to the second notch from the top and the mid range seems better but I still get the hesitation.

I haven't tried adjusting the air screw yet.

My main is a 150.

[luvmyex]

turn the air screw out little at a time till it stops.

[countypark]

I am pretty sure it is out 1.5 turns.

I read that if the pilot is to lean it will cause the throttle response to lag. If I turn my airscrew out more will it richen the mixture?

[TRX_Thumper]

yeah it will richen it...but it might be best to just go ahead an bump the pilot up one size

[countypark]

OK

I switched my pilot jet from a 40 to a 42 and the quad won't start.

I have my air screw out 1.5 turns which is supposed to be ideal.

It started fine when I had the 40 in. I wonder if I should go down to a 38.

I set my needle to the top clip.

[BADTRX400EX01]

Go back to the 40 pilot, run the bike in the "pilot" zone, then read the plug. If plug looks good you may have accelerator pump troubles. If plug looks lean (doubtful since you said the bike wouldn't start with the 42 pilot jet-I assume it fouled the spark plug?), you need to turn the FUEL screw out in 1/2 turn increments until the plug looks rich, then go back 1/4 or 1/8 at a time until it looks good. don't pay much attention to what the "optimal" setting is supposed to be, you have a built motor, and bigger carb. Turn the screw in if the plug looks rich. BTW, the four stroke carbs have fuel screws, which by suggestion of their name, means that they control the amount of fuel for their given range. On these screws, turning the screw out richens the mixture, because it is letting more fuel in. On two-strokes there is an air screw, which by name suggestion meters air in their given range. Turning these screw in richens the mixture because you are getting less air in the mix. Hope this helps!!

[SUPERFLY 400]

I had the same problem with my 400. My problem was that I did not let the bike warm up. Try riding around to warm the engine up, then put in 1st gear and go full throttle. It will either bog out or you will land on your *****:D Make sure your plug is clean before you go out. You need to have your bike warmed-up before making any final adjustments. Don't make sense to adjust a carb on a cold motor!;) Good Luck!

[toby400ex]

My 400ex is bugging the chit out of me with this jetting, ive been using the dynojets instructions, using a dj146 main with the airscrew out 3.5 turns and needle clip on the 3rd groove. Today i went from the recommended dj146 to a dj142 yet the plug is still black, should i try turning in the airscrew till the plug is the right color. It seems to run perfect but, but i want the plug too be right.:(

[TRX_Thumper]

countypark before i sold you the carb i had it on my stock 300ex with a DG muffler and uni filter...i had a 40 pilot in it and i first treid a 128 main...it ran but was extremely lean..i threw a 145 in it and it ran pretty good..needle set in the middle spot...it was pretty spot on perfect then...i actually found out that with the 400ex carb i needed a larger main than with the 300ex carb

[RIDER11X]

I could be wrong, but these symtoms sound likea pilot jet being too rich. I would try the 38 pilot to see if it clears up. The needle should not be a factor in this kind of a problem. But don't just take my word for it, check around.:)

[countypark]

Ok, here is where I ended up.

I went up on my pilot and the quad wouldn't start, so I went down to 38 and it still wouldn't start.This was with the pilot screw set at 1.5 turns out.

So I put the 40 back in and the quad starts and idles fine.

I turned the pilot screw in to 1 turn out and eliminated the hesitation.

I set my needle clip to the 2nd postion from the top and I have nice throttle response.

I had a 150 main in and the quad broke up at WOT so I dropped to a 138 and it winds out nicely but a little lean. I tried a 145 and it still broke up so I think I will end up with either a 140 or 142 main for optimum top end.