400ex Carburetor Probs.

[Dalex]

I just bought a 400ex it has been sitting for about a year and the carb was pretty gunked up, I cleaned it out several times all jets are clean, but at low and mid throttle, under a load it spits sputters and smokes. The diaphram doesn't have any holes or cracks. I just don't know what else to do. the nut on the jet holder (that holds the main jet) may be part of the problem, does anybody know where that should be set ? I didn't pay any attention to it when I disassymbled it. AT high RPM's it seems to be ok , but if i try to go from slow speed to mid range on an incline it acts up.

BTW what is the proper spark plug gap for the 400ex?

All jets are stock 38 and 148

Any help would be great, I am all out of ideas.

Thanks for reading.

Dalex

[Spikers400]

make sure your gas is good, drain it and replace it.

[Dalex]

I did put new gas in it. but there may have been a half a pint of the old gas left in the tank that I forgot to remove, do you think that could be screwing things up? I filled it to the top with 92 octane.

[Dalex]

could this be an electrical problem?

[Spikers400]

Go to the powertrain section and read the thread i made. I had the same question about the mainjet holder thing.

"that makes a big difference on power. this piece that the mainjet screws into is called the needle jet holder. you will see a nut on this piece. you need to screw the needle jet holder into the carb and tighten the nut so you can still see 2-3 threads left on the needle jet holder. making sense?? Cals400ex

I would try that, i doubt its electrical, if it starts ok.
Plug gap- .025"

[Dalex]

I did read your post earlier, but I am at work right now so I can't check it, I think I set it to three threads showing but not sure, I had it turned up and down so many times.

thanks for replying,
Dale

[mojoe2878]

did you make sure the small hole in the carb it self was clean? the one where fuel flows through to get to the engine adter it passes the pilot jet is the one im talking about. take the pilot jet out and blow compressed air through the hole where the pilot jet screws in and make sure its clear. it sounds like a pilot circuit problem since its doin this at low speed and at low throttle position.

[Dalex]

Yeah I blew out the holes good. It sounds like it is starving for air
but I can't find any obstructions, i'm gonna try a new plug in it .

Is DPR8Z the correct plug number? (NGK)

[mojoe2878]

yeah thats the right plug

[Dalex]

ya know I also did a valve adjustment on this, could that affect the mid-range like that, if I mis-adjusted it? It's not backfiring though.

[mojoe2878]

yeah that could effect the performance. if their too tight then the valves wont fully close and if their too loose they wont open all the way.

[Dalex]

Well after :
re-adjusting the valves

installing a new spark plug

and adjusting the nut on the main jet holder down to 2 threads

my 400 is running alot better, I took the airbox lid off and that helped a little too (I will put that back on though)now nstead of missing and bogging , but when I take a small hill slowly closer to the top it ( when the incline is a little steeper) it starts acting up a little like it is not getting gas (or is getting to much cause it's smoking a little) maybe I should turn that nut out one more thread so that there are three threads showing.

[cals400ex]

i wouldn't mess with the needle jet holder if it is between 2 and 3 threads showing. going with 3 showing is going to lower the mainjet in the carb. remember, when we are working on this the carb is upside down.

what are the mods on your bike and what jetttign you run?

[Dalex]

I took my friends Carb off and measured his jet holder which has never been apart it was .959 in. from the bottom of the nut to the top of the main jet. (I based my mic. off of the tab that is made into the carb to hold the baffle in place) ask me if you don't uderstand that.

I hope that measurement might help someone who has that problem , even if it is not right for your application it will give you a basic area to start.

I have stock jet installed ,148 main.