not running right?

[jak1389]

hey everyone, i just got finished rebuilding my motor to a 426. i started the jetting at 165 main and 40 pilot. the 165 seemed alittle fat, like it would die and not idle, and have a little ploop sound (sorry, but that best describes the sound). it was not a loud pop like the sound of a lean motor. i moved it down to 162 main and now it pops alot, and when i get to about 1/2 throttle it boggs and feels like its about to die, until i let off the gas. when i rode with the 165 it was the first ride on the fresh motor. i am still breaking it in, and figured i would try and tune the jetting alittle bit better, but i seem to have made things worse. would the 160 actually be too rich, and that is why it is bogging down. i rode it with the 160 for about 5 imn and it seemed to be ok, and then all of a sudden it boggs down at 1/2 throttle. i am bamboozled and need some help. thanks alot.


~jason

[jeremy_283]

what altitude are you at?

[jak1389]

my elevation is 1013 ft. can someone tell me what symptoms they are, if its too lean, or rich or what? thanks for any help

[sixer3]

the popping is a lean symptom, not idling would have nothing to do with your main jet, a 40 pilot sounds a bit small try a 42 and 45, also loosen your mixture screw out another half a turn, try running a 170 main, maybe bigger?...see hoow it runs like that, if it bogs down till it dies, your probably a little rich on your needle, have you adjusted the clip on your needle at all?

[jak1389]

i believe the clip on the needle is on the 2nd notch from the top down. ill try putting the 165 back in tomorrow and give it a test and see if it runs any better.

[GPracer2500]

Originally posted by jak1389
i believe the clip on the needle is on the 2nd notch from the top down. ill try putting the 165 back in tomorrow and give it a test and see if it runs any better.

I believe the stock needle position is the third position (the middle slot). 2nd postion would be leaner and too lean. In my experience, the only reason you ever have to go leaner on the needle (on the 400EX) is to accomidate high elevations. Move it back to stock and that should help with your 1/2 throttle running issue.

Remember that the needle is the primary circuit for about 1/8 to 3/4 throttle and the main is the primary circuit for 3/4 to full throttle. There is bleed-over between the ciruits, but focus on each circuit individually.

http://www.sparksracing.com/center/400ex/calib_chart.gif

[jak1389]

ok i have figured alot out since ive been on last. the reason it all of a sudden started bogging at half throttle is becuase my choke was loose and from riding around it bumped up and was on. i cant figure out how to tighten it up so i just zip tied it open. i brought the main jet down to a 155 since a buddy said the popping could be from excess gas in the exhaust. much better throttle response. it still pops alittle after i let off and the plug is dark. a car fanatic friend said that it might be possible the overlapping of the valves becuase of the aftermarket cam may cause this, since it does in the car world. does this sound like it is the case with me, or should i keep trying to tune it? thanks

[GPracer2500]

When does it pop? Is it a sharp, crisp POP or more of a wet sounding BLAPP?

[jak1389]

it pops on deceleration. i believe its more of a crisp pop but im not sure if i would be able to tell the difference.

[sixer3]

pop on decel is almost always an exhaust leak or even more commonly a lean pilot jet and/or air-mixture placement, unscrew your mixture jet 1/2 turn and throw in the next size pilot and the backfire(pop) will go away, excess gas doesnt usually create a backfire unless its causing detonation which usually if its doing that you'd be having a lot more questions other than there is a pop sound, good luck

[GPracer2500]

Try a 42 pilot.

[jak1389]

ok i have a 40 pilot now, i just got a 42 today, so ill try the 42 pilot and ill mess with the mixture screw and see how it is.

all my 4 wheelers/dirtbikes poped when letting off the gas without the clutch engaged