[YellowTrx400]

Hey guys, new to the forum, been working on my 2001 400ex and it’s popping on decel and doesn’t want to idle. I’m going to pull the jets out tonight and see what size they are. It has DG header and slip on exhaust with stock air flitter. Depending on jet size, if it’s stock what size do I go to?

 

[SlammedRanger]

Depending on altitude and ambient air temp of where you live. But probably is the ball park of 170-175 main and a 42 pilot jet.

 

[YellowTrx400]

Depending on altitude and ambient air temp of where you live. But probably is the ball park of 170-175 main and a 42 pilot jet.

So I was thinking of doing a 175 main and 42 pilot with the mixture screw somewhere around 2.5 turns. I’m in California

 

[SlammedRanger]

Sounds like a very good place to start!

 

[LedFTed]

how far are you above water=altitude/where you live. i'm close to 600ft :smile

 

[LedFTed]

how long have ya had the 400, an how long has it been popping? is it backfiring through the exhaust?

 

[YellowTrx400]

how long have ya had the 400, an how long has it been popping? is it backfiring through the exhaust?

I’ve had it for a couple years. Started popping a while ago and stopped riding it. Want to get it going again. It seems to be backfiring through the carb. I’m about 200’ in elavation

 

[LedFTed]

i think that puts you in a different ballgame. then the carb, it could have to do with a valve or timing. i doubt the carb does this.

 

[SlammedRanger]

i think that puts you in a different ballgame. through the carb, could have to do with a valve or timing. i doubt the carb does this.

It can do this when its extremely lean at idle. It will cough and stall usually. Although alot of times its also a sign of a stretched timing chain.

 

[LedFTed]

i think that puts you in a different ballgame. through the carb, could have to do with a valve or timing. i doubt the carb does this.

It can do this when its extremely lean at idle. It will cough and stall usually. Although alot of times its also a sign of a stretched timing chain.

my 2000es used to backfire on deceleration.. could it be that a lean mixture, would have the opposite effect. i also noted while looking for the reason the 2000es back fired through the exhaust, some sites said it is normal, for that model, to run rich, an backfire, on deceleration.. i beg to differ. once i got the carburetor, rebuilt right, adjusted right, it quit doing it after the carb rebuild. ed

 

[SlammedRanger]

Yeah popping on decel is generally a main jet issue. Coughing and random stalling and no idle is usually a pilot jet/mixture issue. In most cases the popping is caused when the main jet is very lean and it dosnt detonate the fuel clean and it builds in the header and ignites and pops. It can also be caused by an exhaust leak or even a partially blown headgasket. Pulling to much air in and causing the lean condition. But on the 400ex motor that i am very familiar with. They almost always have a slightly stretched timing chain. Which just adds to the problems throwing the timing off alittle.

 

[YellowTrx400]

i think that puts you in a different ballgame. then the carb, it could have to do with a valve or timing. i doubt the carb does this.

Just pulled the jets out. It’s got 148 main and a 38 pilot, to small for having the header and slip on exhaust correct?

 

[SlammedRanger]

Yep thats stock jetting

 

[YellowTrx400]

Yep thats stock jetting

So should I go 175 main 42 pilot?

 

[SlammedRanger]

Thats a starting place. But honestly jetting is different for every engine. It depends alot on your altitude and ambient air temp. Shoot even berometric pressure has a role in tuning. The only question will be the stock filter. And im guessing here. Stock airbox lid still?

 

[YellowTrx400]

Thats a starting place. But honestly jetting is different for every engine. It depends alot on your altitude and ambient air temp. Shoot even berometric pressure has a role in tuning. The only question will be the stock filter. And im guessing here. Stock airbox lid still?

Yeah stock air filter and lid. Is there any mods a I can do to the stock lid? Drill holes? Take lid off?

 

[SlammedRanger]

You can take the lid off if you dont ever ride in sand or mud. It will be a noticeable gain in throttle response and alittle bump in power. But the sound is what you will notice the most. It will be alot more throaty sounding.