[ItsMichaelH]

Ok, so I've got a 2000 400ex and it runs pretty well, the only thing is that on decel it has a lean pop. I believe its a stock motor with the full yoshi pipe with the header and a uni air filter. The airbox has 3 1-inch holes drilled into it already. I was in the carb and it has a 142 pilot and 150 main. Do I need to go bigger on the main? How much bigger?

 

[SlammedRanger]

Are you sure they a keihin jets? Its not a dynojet kit or anything? If the main jet is a hex shape i would leave the 42 pilot and up the main jet for sure. 150 is 1 step up from stock. 148. For a slip-on and a filter its suggested to run a 155. Full pipe and midified airbox lid i would bet you are going to be around a 165-170. I would also suggest dropping the clip on the needle 1 slot. Should wake up the mid some. My .02

 

[ItsMichaelH]

Are you sure they a keihin jets? Its not a dynojet kit or anything? If the main jet is a hex shape i would leave the 42 pilot and up the main jet for sure. 150 is 1 step up from stock. 148. For a slip-on and a filter its suggested to run a 155. Full pipe and midified airbox lid i would bet you are going to be around a 165-170. I would also suggest dropping the clip on the needle 1 slot. Should wake up the mid some. My .02

Right on, how do you adjust the needle? Not sure what kind of jets they are? I believe the main jet is the bigger hex shaped one.

 

[SlammedRanger]

A dyno jet kit would be a round jet in a holder. Keihin jet would be one solid piece in a hex shape. To change the needle position you go through the top of the carb and take 2 small screws out of the arm that goes down into the slide and one bigger screw out of the slide arm itself and pull the needle up out of the slide with a pair of needle nose pliers. Then change the clip into 1 slot lower on the needle. And do reverse to put it back togeather. I highly suggest a magnetic screw driver or you risk losing the tiny screws down in the slide.

 

[ItsMichaelH]

A dyno jet kit would be a round jet in a holder. Keihin jet would be one solid piece in a hex shape. To change the needle position you go through the top of the carb and take 2 small screws out of the arm that goes down into the slide and one bigger screw out of the slide arm itself and pull the needle up out of the slide with a pair of needle nose pliers. Then change the clip into 1 slot lower on the needle. And do reverse to put it back togeather. I highly suggest a magnetic screw driver or you risk losing the tiny screws down in the slide.

https://gyazo.com/cbd63a837dfd81515c91cca7e31baf73 heres a pic

 

[SlammedRanger]

Thats a keihin oem jet. No jet kit. 150 is way to small for your mods.

 

[ItsMichaelH]

Thats a keihin oem jet. No jet kit. 150 is way to small for your mods.

Ok, so I should be going around 165? Wheres the best place to buy individual jets? https://www.ebay.com/itm/Main-Jet-S...ash=item1a2e16c83f:g:jmIAAOSwCMFaA6pZ&vxp=mtr would this work?

 

[SlammedRanger]

I get mine from jetsRus because its local to me in ohio and i get them next day. But anywhere you can find them. Local honda dealer or most any powersports place can get them. And i would get a 160-165-170-175 to cover all your bases.

 

[ItsMichaelH]

Ok, well today I ordered the Genuine Keihin jets from JetsRUs in the sizes you advised. Hopefully they get here soon and I can get this 400 tuned up.

Merry Christmas btw!

 

[ItsMichaelH]

So after work today the jets came in the mail. I started out with the 160 main and it still had a little lean pop on decel, so I went with the 165.. It's about 7 degrees Fahrenheit outside right now so I didn't get to test it too much, but on decel it might have had a slight pop (didn't get to ride much as it was dark and super cold), but nothing major like before. I'm gonna run it around a little after work tomorrow and see what I'm dealing with. Might have to bump up to 170? Not sure yet. btw - haven't adjusted the needle yet (not sure if i have to) and im just about 3 turns out on the mixture screw.

ALSO: Not quite sure what it is, but seems like this bike idles a little rough like is sputters out the exhaust every once in a while at an idle. Doesn't seem too bad, but any ideas??

 

[SlammedRanger]

3 turns on mixture is telling me you need a bigger pilot jet. You use the mixture setting to find the proper pilot jet size. 2 3/4 or above need a bigger pilot jet. 1 1/4 or lower you need a smaller pilot jet. Thats probably why its idleing weird. I still suggest dropping the needle clip. Your mid power will increase! I promise! LoL

 

[ItsMichaelH]

3 turns on mixture is telling me you need a bigger pilot jet. You use the mixture setting to find the proper pilot jet size. 2 3/4 or above need a bigger pilot jet. 1 1/4 or lower you need a smaller pilot jet. Thats probably why its idleing weird. I still suggest dropping the needle clip. Your mid power will increase! I promise! LoL

Aren't a lot of these guys running the 38 pilot which is stock? I'm running a 42, not sure how much bigger i should go.
Also, i'm curious, how do you typically adjust the pilot jet and know when it's good? any methods?

And you've got me convinced, i'll drop the needle tonight

 

[SlammedRanger]

Depends on alot of things. One is the ambient air temp. Another is your elevation. And barometric pressure plays a part in it aswell. The best way i have found to adjust mixture is to lower the idle till its as low as it can to stay idling. Then turn your mixture screw in 1/4 turn incraments with a few second in between each. When you get it to almost seat or lightly seated the quad should run really rough and maybe even stall. If it stalls put it to 2 turns out and start it back up. If not just start turning it out in 1/4 turn incraments again. You are looking for the highest smoothest idle you can get. If you keep turning it out passed 2 3/4 and the idle is still going up you need a bigger pilot jet. You are looking for between 1 3/4 to 2 1/2. If its in that range your good to go. Now be careful because if its as cold there as it is here you will not be able to tune it in properly until your at your ambient air temp for your area.

 

[ItsMichaelH]

Depends on alot of things. One is the ambient air temp. Another is your elevation. And barometric pressure plays a part in it aswell. The best way i have found to adjust mixture is to lower the idle till its as low as it can to stay idling. Then turn your mixture screw in 1/4 turn incraments with a few second in between each. When you get it to almost seat or lightly seated the quad should run really rough and maybe even stall. If it stalls put it to 2 turns out and start it back up. If not just start turning it out in 1/4 turn incraments again. You are looking for the highest smoothest idle you can get. If you keep turning it out passed 2 3/4 and the idle is still going up you need a bigger pilot jet. You are looking for between 1 3/4 to 2 1/2. If its in that range your good to go. Now be careful because if its as cold there as it is here you will not be able to tune it in properly until your at your ambient air temp for your area.

Yeah it's super cold here so i'm gonna leave it until we get a warmer day

 

[ItsMichaelH]

Ok, it's been some time... but I messed around with the jetting. I've got the 42 pilot in and the 170 main along with dropping the clip on the needle. Still pops out of the exhaust on deceleration. Any ideas? I can't imagine I need a bigger pilot or main with just a stock motor and a full exhaust. Can anything else make this popping on decel? Seems to run fine and have the power it should with the jetting.

 

[SlammedRanger]

With a full pipe, a uni, and holes in the airbox. Yeah you could need more then a 170 main jet. Keep in mind though that when it warms up you will run richer. So the 170 may pop when its cold out. Because its a tad lean. But come summer time it may run perfect. Im in the same boat rightnow. Waiting on the cold to break...