400EX Popping????

[kennyo1]

I have a 2005 400 EX. Curtis Sparks( X6) exhaust, installed a sparks 6degree timing key a few months ago but have not had a chance to take it out. After the key install I started it, and ran around the yard and it seemed to be running fine.

I started again yesterday and it is popping. With it in neutral, it pops while revving, pops on decel and pops at an idle.

Does this sound like a carb problem. It seems like everytime I let it sit, I have to dissassembel the carb and clean it. The jet gets blocked. I have dumped the tank and never found trash.

Should I go through the carb again? Any other ideas? am planning to take it out this weekend if I get it running right.

[zach0199]

Mine does this too even after rejetting i have different exhaust than you but the same senario as you I still cant figure the problem out.

[kennyo1]

I did not rejet or change anything except the timing key. It just started running bad. Does it sound like a card problem? It seems like I have to pull the carb apart and clean it every few months. Is thsi normal?

[CJM]

Some popping depending on the mods is ok. Mine is bored 416cc, 11:1 piston, cam, exhaust, no airbox lid. Mine was popping still even after I rejetted but not as bad.

My mechanic told me it was b/c the cam was letting air in still..

A more stock atv needs to have the jetting redone better if it pops.


Originally posted by kennyo1
I did not rejet or change anything except the timing key. It just started running bad. Does it sound like a card problem? [b]It seems like I have to pull the carb apart and clean it every few months. Is thsi normal?[b]

If you let the gas site in the tank for awhile then yea b/c the ethanol frigs up the carb. Dont let it sit or buy star tron additive (bike shop will have it) to combat the breakdown of ethanol.

[JOHNDOE83]

They arent supposed to pop, I have a 440 with a stage 2 cam, and mine never pops....never.

The pilot jet and air/fuel screw need adjusting, sometimes you can get away with just the air/fuel screw adjustment.

Any more then 3.25 turns out on the screw needs a bigger pilot jet.

The cam will not make it pop, and doesnt keep sucking air still, like that mechanic said.

you need to tune it a lil more.

[CJM]

I had several different sizes in it since I redid it with a buddy and it still popped. We decided it was either the cam still letting in some or the exhaust was slightly off (which it is).

Even so, slightly lean gives you better power overall imho. So long as its not excessive and the popping isnt insane.

Least thats how it always was with my buddys motorcyle, he always wanted it slightly lean.

[JOHNDOE83]

Yeah but the poping would be from the pilot jet, and that has almost nothing to do with performance.

The pilot only works from 0 to 1/8th throttle. and slightly rich on the pilot gives you off idle torque.

trust me! its the pilot jet or air fuel screw.

[CJM]

Originally posted by JOHNDOE83
Yeah but the poping would be from the pilot jet, and that has almost nothing to do with performance.

The pilot only works from 0 to 1/8th throttle. and slightly rich on the pilot gives you off idle torque.

trust me!

I got ya. His is probably off in jetting, I know my exhaust is leaking ever so slightly in my case.

[zach0199]

im running a 42 pilot and 2.5 turns on the a/f screw what should i look to change to help with the pop

[JOHNDOE83]

if you take your air box lid off does it make it worse?

[zach0199]

Havent rode it with the lid off, if its better or worse were do i go from there the a/f screw? Would i be able to tell instantly if I took it off?

[JOHNDOE83]

I dunno, I dont know how bad it is now?

take it for a few spins with the lid on now, then take it off and go for a few, then try it on again, and let me know...lol.

if its worse, you need to turn the air/fuel screw out more or maybe even get a bigger pilot jet?

I have a 440 that doesnt even pop if I run it without the slipon.

[zach0199]

Ok just took it out it runs alot worse with the lid off almost wants to stall out with decell and idle speed in first gear.

[JOHNDOE83]

turn the air/fuel screw in all the way, then turn it out to 3 complete turns and see if it helps at all.

[kennyo1]

I don't believe that it is the jetting. It ran fine before I put in the key and ran fine right after.
Could it be possible that it is the carb?? Doe spopping ussually point to the pilot jet?

Maybe I'll dump the tank and take apart the carb again tomorrow.

Where should I adjust the A/F screw ?

[zach0199]

i turned it 3 turns its almost completly gone should i go to 3.25 turns or jet up the pilot its a 42 already and my mod list isnt crazy does this poping effect anything my fuel is a little old to could that be subject also?

[JOHNDOE83]

kenny, sometimes the pilot jet will get clogged from bad gas, but that still means its the pilot jet thats making it pop.

zach, if I were you id either turn it out 3.25 or go up 1 more size on the pilot jet.