400ex Carb on 350x PROBLEM

[350xx]

Hey guys.
So my 350x has a k&N and a freeflowing exhaust, otherwise its stock.
So i finally got a 400ex carb all rebuilt and put on my 350x.
After 50 kicks it starts.
I turned the pilot to 2.5 turns out and it doesnt really want to idle.
you give it a tiny bit of throttle and when you let off it goes pum pum pum.
when you give it 1/4 throttle, maybe a bit more, and then let off it goes pum pum BANG!!!! BANG!!! lotsa backfiring.
So i turned the pilot out more, to 4 turns, still backfiring but idles a little better.
I put a new plug in before i did this.
Took the plug out and there was no black at all, white.
LEAN right?

But i cant adjust the pilot out anymore..
Any clues guys?
Thanks!

[Twilight]

Need new jets in the carb. What are the jets in your 350x carb? You need to do some trial and error probably.

Also make sure there is no air leaks.

edit; 42 pilot jet and a 165 main should help you

edit2; bad fingers...

[350xx]

Im using the stock jets for the 400ex in the 400ex carb.

[Twilight]

thats not much help, what are they?

[350xx]

The slow jet is 38 and the main is 148

[Twilight]

have you made sure theres no kinks or bends in any of the cables?

[3wheely]

Sounds like way lean to me. Do you have the stock filter to put on and try for now? K&N's allow a lot of air flow and will cause lean conditions. It might be enough to get by until you re-jet. I had to do this to mine.

[350xx]

Im thinking it needs jetted differently. With my 350x carb it ran perfectly.

Cables are all fine.
What do i need to change to get it to run richer?

[3wheely]

On a stock carb and stock bike it's 1-3/4 turns out. Obviously it would be different with a 400ex carb, exhaust and filter.

[3wheely]

Go smaller. It's trial and error. Buy a few to save time.

[350xx]

yeah, i have it at 2.5 turns out, but super lean still..

[350xx]

go smaller what? main jet?
Why does twilight say to go larger on the slow jet?

[3wheely]

I thought the further out the leaner it gets? Have you tried less turns? If still no difference you probably need to re-jet. Have you went to the technical section and read the thread about tuning and jetting? It's pretty helpful.

[Twilight]

the jetting i gave should be the equivalent and will get you on a good start. run it on those settings for a ride, take out the plug and do a plug chop. From there you can either post pics of what it looks like, or you can go from there and find the perfect jetting.

[3wheely]

They both do different things depending on the setup. Read up on that thread. It's very helpful. Jetting is never fun.

[Twilight]

OOPS my bad.

165 main and a 42 pilot.

Sorry, always start out too rich. I have the slippy fingers. If you wanted you could always go 170 to start as well.

[350xx]

Okay, i have some jets in the shop and i will try out the main jet first since thats an easy swap.
I have the stock 40 pilot from the 350x i could put in after i see what the main does.

[350xx]

I read the jetting 101. It says the main jet is for higher rpms and to check it, run at WOT for a couple seconds then shut it off immediately and pull the plug. if still lean, then i will go up. Next would be the needle, because if it is too far in, then i wouldnt be getting enough fuel. Then my screw adjustment. Im thinking i need a bigger pilot jet because if i rev it, it slowly returns to idle and thats an indication of too lean.

[3wheely]

Twilight was right go larger on the main and adjust from there. My bad I confuse myself sometimes. Once you get that straight see what you got at 1/4 throttle. Adjust the needleclip for this (up for rich down for lean) then go to the pilot. Then you should be able to fine tune.

[3wheely]

Pilot effects up to 1/4 throttle.

[350xx]

Okay so i put a 160 main in and gave it near full throttle for 2 seconds, then shut it off and pulled the plug. still very light.. It runs fine at upper throttle, but when i let off it backfires like crazy.

[350xx]

How do i adjust the needle? i have the top part off, what now?

[Twilight]

Is the engine getting too hot?


take the slide out, then adjust the needles spot with the circlip.

[3wheely]

Move the clip up to richen.

[350xx]

I moved the clip up so its on the 4th notch down from the top.
There isnt much noticable difference, and still running pretty lean with backfiring.
160 main
4th notch
38 pilot
will idle okay, but occasionally pops and sometimes dies randomly.
throttle response is good all the way through, but its just backfiring so much. POP POP POP!

[Twilight]

go to a 170.

internet jetting is impossible, buy ill try and help.

[350xx]

I went to 168 because thats the biggest i have.
It will go full throttle with no sputtering and this thing flys! But my low end is kinda poppy. Like i let off it will pop and backfire. im thinking my next step is to go up on the pilot jet.
current:
168 main
38 pilot (have a 40 in 350x carb, idk if it will fit)
2 turns out on the fuel air screw

Doesnt really like idling, sputters and pops occasionally. if i turn the idle up it will idle fine, still popping, but if i turn it to what it should be, it chugs and dies.

[350xx]

OH, and i did a plug chop after racing around, The tip is very light, ceramic inside is white, threads are darkening from heat but thats about it.

[3wheely]

I believe that would be the pilot at this point. The only way to find out is change it. The main has nothing to do with idle.

[just ben]

haha the blind leading the blind. I am guessing from your sound or typing affects that its back firing? That is usaully a sign of a rich condition. The backfiring is the excess fuel igniting in the exhaust.good luck

[350xx]

It does backfire. yes.
When i let off the throttle.
That does mean it is rich..
should i try going down on the needle, aka up 2 clips.?
The only thing confusing me is the fact that the plug remains white and dry.. Hmm.

[3wheely]

Did it back fire with the stock carb? I had an exhaust leak once and it backfired like crazy until I fixed it. Is the float level? Still seems lean to me at least that's what the plug shows. It's all trial and error especially with a different carb.

[350xx]

It only popped when i was going downhill before, or if i got it really high in the rpms and then let off and let the compression slow it down.

Im thinking of going to a different pilot. I will buy a 42 and a 34 or 36 and try those.
Thats very time consuming though.

IF it doesnt sputter at WOT then my main jet shouldnt be too big right???
I think my idle is too rich or too lean. since it dies by itself sometimes. hmm.

[350xx]

Okay guys.
I think the pilot jet is the culprit.

I turned the fuel air screw out to like 3.5 turns
Got rid of most of the backfiring, however there is still some popping at very low throttle, under 1/4.
Pilot effects idle thru 1/4 and thats where I am seeing issues.

A smaller pilot jet it is.
Then i will have to re-adjust my fuel air screw possibly.

If there are any disadvantages of having a huge main jet please speak up. Because my throttle response is perfect and it doesnt sputter anywhere throughout the throttle range, and WOT has no sputtering whatsoever.

[3wheely]

Sounds like your on the right track. Just remember the spark plug will tell you all you need to know. A goldish tan color is what your aiming for and obviously a good running bike.

[350xx]

Yup :]
Getting a pilot tomorrow.
Right now im at 38..so i will try a size or two lower. im thinkin, with the amount of sputtering i will only need to go to 36. so we will see. depending on price i may pick up more.
The plug trick isnt working for me. no matter what ive done it says lean. So i will do this, see how the sputtering goes, and get a good half hour of riding or so. and then check the plug and see what it looks like.

[350xx]

First off, I will try to bring the clip up, lowering the needle.

[3wheely]

Yes, I would say 4 down is still low.

[350xx]

stock setting on needle is good. Now i just need to go to my local dealer and get a smaller pilot jet.

[350xx]

Still waiting on a response to: If there are any disadvantages of having a huge main jet? WOT doesnt sputter at all, it just rips!!

[3wheely]

You could always switch it out with a smaller one to verify. Only takes a few minutes. If it doesn't sound right then your probably on the right track. Doing plug chops you really need a few new plugs. There's no real answer. Every bike is different.

[Dirtcrasher]

My 3560X carb has a 50mpilot and a 160 main an is still off......................

I give ya credit for trying :beer

[350xx]

Okay, went to my dealer and they didnt have any!!! they could get it shipped and my total cost for one slow jet would be 20 dollars. Screw that.
EBAY HERE I COME!!!
This will work.
I know it will.
Going for
168 main (may drop to 160)
35 pilot (should lean out the bottom end some)
3rd clip on the needle AKA stock.
Currently 3.25 turns out on fuel air
NEED TO GET CORRECT STOICHIOMETRIC RATIOOOO haha
:Bounce

By the way 3 wheely and twilight, thanks for the help.
After some good reading and tests I have a better understanding of these overcomplicated carbs.

Total invested: 39.50 for carb (needed work), 7 for main jet, new slow jet will be 7. And some hours of testing and work past and yet to come.
Better than paying 100+ for a perfect carb and still having to go through the grueling jetting process.
Vid and pics in a new thread maybe sometime.
Ill keep ya updated. Thanks again.