Help with 400ex carb

[dripinc09]

1999 400ex
k&n and White Bros E series with no baffle

Not* origional owner

I have been fighting with this thing for quite some time now, always seemed to be running dog rich. My first attempt at resolving my issues I found the previous owner had a 165 main in her. I thought that was really too big so I downsized to a 152 ( I think I was suggested that size from somone on this forum). That was a no go, backfired like crazy and loss of power, so that way lean as piss I assume. I threw in a 155 for the time being and called er good for the moment. It does not seem like she has the power I felt with the 165 in. But with both the 165 and 155 had my plug fouled, even after messing with the air screw.

(on the trails people behind me could smell unburnt fuel outa my tail pipe)

What I just realized:

In my Claymer it directs the needle to be adjusted to 3 down from the top which is the stock position, so I had done that while messing with my jets. What I had just realized was in the Clymer manual the Needle in there has 5 slots, and mine has 6 slots... Is this an aftermarket needle posibbly? And if so do you think I need to try 2 from the top instead to lean it out a bit?

Im not a carb expert by any means, which is why I am asking help from you guys

hopfully somone will throw in their 5psi (2cents)<<-Im a turbo guy

Thanks
in advance!

[CJM]

If its backfiring on decel its either an exhaust leak or the pilot jet is to lean.

Heres what you should do:
Put a 155 in it, needle 3rd notch from the top-top is the non pointy end (it does sound like you have an aftermarket needle both of mine have 5 notches but it shouldnt matter to much), and turn the air/fuel screw out 2.5 turns and see what happens. Your pilot jet should be a stock 38, might want to try upping to a 40.

But really if it backfires alot look at the exhaust and look for carbon build up (black), its probably an exhaust leak.

The needle, and main jet really dont have that much effect on decel.

[honda400ex2003]

i would be willing to bet that you have a dynojet needle. I think they are 6 slot and would probably make it near impossible to tune with it in there.

the dj needle either makes the mid super lean or too rich without shimming it up to get it inbetween the 2 which may be an option for you to get it close. I would rather see you get a stock needle and go from there for ease of tuning without a dj jet too.

i still suggest a 152, stock needle 3rd notch, and a 42 with 2.5 turns out on the f/a screw.

if you could get your hands on a 138 dj main with the rest of the dj stuff including the main adaptor you could run the dj needle on the 3rd notch and the 138 dj you would be good to go.
steve

[dripinc09]

I currently do have a 42 and the air screw is 2.5 turns out.

With a 152 (and the dj needle on the third notch) I got a nasty backfire on accel.

I will try to pick up a stock needle this weekend and report back my findings. Thanks alot for the help!

[CJM]

Yes, the DJ needle could be causing issues.

The pilots rather rich as well for just a slip on but it will work.

Try this: Start the quad up, take your hand and stick it over the exhaust and see if you can detect any leaks-you got leaks then the exhaust is leaking causing a lean condition when you let off throttle.

[dripinc09]

Well I got a whole rebuild kit for her over the weekend and built it up and installed the fresh carb Saturday evening. Today I went and got my summer tires put on and was able to test out the carb work. It runs way better! It is smooth through the throttle and doesnt smell like raw fuel any more. Looked at the sparkplug and it looks almost perfect.

Before It was damp and fouled before the rebuild.

My issues seems to be resolved. Thanks guys for the help!

[honda400ex2003]

what did you end up with?

152, 42, 2.5 3rd notch?

steve

[dripinc09]

155, 42, 2.5 turns a/f screw

I am starting to think there are some aftermarket parts in the motor. I will take a deeper look when I replace the timing chain/tensioner later this summer.