Popping when letting off throttle.

[Zakradu398]

My mods are in my sig. Before I did a header, no lid and uni filter. I could go WOT in 5th, let off the gas and it wouldn't pop at all. Now when I do it, it still only does it 2 or 3 times real small but I like it to be spot on ;) EDIT: This is with a 42 pilot. Should I go out on the air screw?

Also, with these mods and about 900-1200 ft elevation does a 155 main seem right? I mean it runs great.

[2003TrX400eX]

might not be gettin enough air

[CJM]

Originally posted by Zakradu398
My mods are in my sig. Before I did a header, no lid and uni filter. I could go WOT in 5th, let off the gas and it wouldn't pop at all. Now when I do it, it still only does it 2 or 3 times real small but I like it to be spot on ;) EDIT: This is with a 42 pilot. Should I go out on the air screw?

Also, with these mods and about 900-1200 ft elevation does a 155 main seem right? I mean it runs great.

First try unscrewing the air/fuel screw so its 2.5 turns out and see if the popping goes away. It doesnt try putting a 160 in there and check the plug/

Whats the plug look like now?

Also put the lid back on and see if it goes away before you do anything else, it does your lean.

[Zakradu398]

WAs already at 2.5 and I took it out to 3 b ut it still does it

[CJM]

Up the main slightly maybe 1-2 sizes, see what happens.

I have a similar issue but the pops arent to bad. When I had the EX carbon there they were mild-moderate pops and I was going to do a 45 pilot, never did tho.

[Zakradu398]

It's not bad at all. like i said, 2 or 3 tiny pops but I just want it to be spot on for piece of mind

[CJM]

I wouldnt worry if its just some mild pops like that. It pops loudly then its a problem.

Up your main 1 size see what happens.

[rageatvlawson8]

could be a exhaust leak as well. If its got a leak it will pop on deaccel. try screw and pilot jet

[2001400exrida]

The main jet has absolutely nothing to do with popping on decel. I would ignore the advice given about upping the mainjet.

If you're getting popping on decel it's your pilot circuit. Since you're already 3 turns out on the screw i would up your pilot jet 1 size and then bring your a/f screw back down to around 2-2 1/2 turns.

popping on decel is a notoriously lean pilot condition, it's an easy fix sometimes. My 450r pops on decel and there is no way for me to get rid of it, i've put 3 different exhausts on there and messed with my jetting more times than i can count. I simply live with it, lol.

[Zakradu398]

Its not an exhaust leak for sure. Whats the next size pilot from a 42? 45?

[ride red 14]

42 is plenty big on the pilot jet. Did you replace your crush gaskets when you put your header on?

[CJM]

Popping can be a lean condition that lies between the overlap of the main, pilot and needle.

It can also be an exhaust leak. Turn the quad on, stick your hand with a glove over the end of the exhaust. You hear air escaping you got a leak.

Ex: with a 42 pilot, needle 3rd notch and a 170 main my bike would pop a bit if I went WOT and downshifted to slow down really quick. The overlap from the main, pilot and needle wasnt enough. Upped to a 172 and it barely popped. Was I slightly rich on the main, yep but the overlap was richer at the higher end and helped with the popping.

Ex 2: Using the 450r carb and a 52 pilot, 170 main and needle 4th notch-no popping whatsoever. HOWEVER it was too rich of a pilot and was flooding when trying to start sometimes. Switched a 50 pilot, slightly lean no more issues starting and slight popping.

Being slightly lean on the pilot wont hurt anything. You make it to rich the popping goes away, too lean and your SOL-you want a fine balance.

If anything if your doing like I did and going from WOT 4th-5th gear and then letting off completely to stop then downshifting and it pops its gonna happen no matter what. You just fed the engine and carb massive quantities of fuel and now your cutting it off.

FWIW I tried a 45 pilot with the EX carb and it was way too rich. Live with slight popping or be rich, your choice.

[Zakradu398]

Guess I am just over-reacting about this. I know on some higher hp things such as my bike (yz450), it will pop no matter what. I just figured I could eliminate it. Thanks though.

One more question. Say im in 3rd-5th gear at low rpms. I hit the throttle to fully open. It seems once the revs hit about half way to open, it picks up a lot more power. Is this a jetting problem?

It's not a clutch either. I just put a new Tusk clutch and hd springs in. (which is awesome by the way)

[CJM]

Wheres your needle, 3rd notch? Try moving it down to the 4th notch.

[2001400exrida]

the popping, especially if it's minor, is definitely not going to hurt anything. But no matter what has been said here, popping on decel indicates a lean pilot circuit.

There is no such thing as circuit overlap. If you give full throttle in 4th gear and then let off and decel and it's popping then you are a hair lean on the pilot. Severe popping would mean you are way too lean on pilot, if it's minor popping on extreme decel it's mostly normal.

I can't stand poor carb advice, when somebody tries to tell you to up the main jet because it's popping on decel that is the wrong advice, there is no such thing as carb circuit overlap, they are all independent circuits. Popping on decel can be 1 of two things. An air leak, or a lean pilot, that's it, the main jet is not the cause here.

[Zakradu398]

I think I have it on the 3rd or 4th. Probably 3rd though.

[2001400exrida]

Originally posted by Zakradu398
Guess I am just over-reacting about this. I know on some higher hp things such as my bike (yz450), it will pop no matter what. I just figured I could eliminate it. Thanks though.

One more question. Say im in 3rd-5th gear at low rpms. I hit the throttle to fully open. It seems once the revs hit about half way to open, it picks up a lot more power. Is this a jetting problem?

It's not a clutch either. I just put a new Tusk clutch and hd springs in. (which is awesome by the way)

I"m not sure why CJM has referred to your needle setting because what you are talking about has to do with the main jet. Anything at full throttle is the main jet, the needle has nothing to do with full throttle. You may be either too rich or too lean on the main jet if it's not giving you full power when you give it full throttle. I would go up 1 on the main and see if it helps or worsens. The needle setting has nothing to do with what you are describing, you're describing a full throttle sympton, not a half throttle symptom.

The reason i'm standing up in this thread is because i built 2 400ex's and did tons of carb adjusting and CJM was always there to give advice, but there were many times when his advice only created new problems or made things worse. Please respect my advice and understand i've tuned 400ex carbs for 5 years now and I know that if you're not feeling all the power you should have at full throttle, you need to adjust the main jet, not the needle.

[Zakradu398]

Not when I'm giving it full throttle. I said when I am at WOT and LET OFF and its decellerating.

[CJM]

The pilot, needle and main jets overlap...

http://www.exriders.com/vbb/showthread.php?s=&threadid=445695&highlight=jetting+placement

Also like I said earlier, up to the next main, 158. How your plug look Zak? Still gives you an issue adjust the needle since it fine tunes everything.