Just got a 400ex used for my 450r :).... Need help

[lumi]

Alright well,

I was reading the DIY and such,

I changed the oil and oil filter today with a OEM oil filter and filled it with HP4 oil.

I then got a new OEM air filter

I also adjust both the intake and the Exhaust valves to spec.

The quad seems to be completely stock except for a White brothers E series slip on.

Here is the STORY:

The quad back fires and pops loud when i am on the gas lighty and when i release the throttle.

It wont stay running on idle aswell. and bogs and dies sometimes.

So i tore into the carb and i found these jets:

The main jet is a 165 and the pilot/slow jet that is next to it is a 38.

And as for the A/F screw, i am not sure how many turns out from in it is suppose to be


Can you guys help me and tell me if this is a jetting issue?

What is the stock main jet and slow/pilot jet?

How many turns out from all the way in should i turn out the A/F screw?



Thanks alot!!

[jelrod05]

the stock main is 149,pilot is 38,and screw should be at 2.25 turns out from lightly seated

[storms400ex]

stock main is 148

[clemsonteg]

Originally posted by jelrod05
the stock main is 148 ,pilot is 38,and screw should be at 2.25 turns out from lightly seated

Fixed it for ya :D

And if you have the airbox lid on and it is stock except the slip on a 158 would be the absolute max main I would run, probably between a 152-155 to be right

[lumi]

Yea stock airbox and the lid on with OEM airfilter.

Alright yea sounds like the Main is wayy too big and the Screw is def turned out too far..

going to the shop tomrrow and get a new stock main jet and adjust the crew.


P.s. what is with the nut on the main jet anything i should do with that?

Thanks alot for the fast replies and help guys!

[Sinister95Z]

While you are in there, try a 42 pilot. It is a very popular pilot size that makes starting much easier. There is a how to in the "Articles" tab up at the top of the page.

My suggestion would be a 42 pilot, 50-52 main jet and the screw 2 turns from lightly seated.

The nut you see is part of the main jet.

[Sinister95Z]

You may also want to check out the needle and clip position. You said that the problem exist when you are on the gas slightly. The main jet only afffects 3/4 throttle and above. Pilot jet is from idle to 1/8 throttle and the needle and clip position is 1/8 to 3/4.