More Jetting Woes Part 2

James Dean,

Thank you for the info. I took apart the carb again just to make sure that nothing was clogged and that the accelerater pump was working ok, everything checked out fine. So I put in the 170 main and the 45 pilot the fuel screw is at 2 turns out, Needle in the third position from the top and I put in a new plug. I went riding and for 10 to 15 minutes everything was ok. Then it started running choppy (best way I can think to describe it), but it never quit, it will idle now and doesn't sound like it is going to die everytime you let off of the gas. I rode the last mile home at about 1/8 to 3/8 throttle. That seems to be where it runs the worst. As soon as I got home I pulled out the plug, from the base of the electrode up to the tip was sooty black but just the very tip maybe 1/16 of a inch was light grey almost white. My take on this is that I need to drop the main jet to a 168 and riched up the fuel screw a little. Does that sound ok or should I try something else. Also can I still use this plug and get a accurate reading or do I need to put in a new one. The friggin thinks are going to break me. Thanks for you help.


It has been in the high 40s to low 50s here so I don't think it is col enough to partially cover the radiator. Thank you for the help anyway.


I don't follow you on the plug chop. I'm not familar with that term what does it mean. Thank you.

[This message has been edited by GRC (edited 12-22-2000).]

plug chop

ride it flat out in top on a road & hit the kill button with the throtle still wide open. clutch in & freewheel to a holt. as it's impossible to do this i suggest flat out, pull in clutch, let go of throttle & hit kill button.

your reading isn't worth bothering with. go by the seat of your pants & how it felt. JD will help you.


Now I understand, Thank You.


The main jet won't help for 1/8 to 3/8 throttle jetting problems.

The needle clip/diameter and pilot/pilot screw are the things to adjust.

Suggest you try both out and in on the pilot screw by 1/4 turn. You then should consider clip #2 on the needle, DRS#2 is close to DVR#4, stock YZ400 needle setting.

This may seem backwards, but the needle at #3 could have been borderline rich before with a lean pilot jet. Richening the pilot made it idle better at the expense of an over rich 1/8-1/4 throttle.


James Dean,

I went to 168 main and 45 pilot Fuel screw back in 1/4 of a turn. THE BIG BLUE BEAST IS BACK!!!!!! Wheelies out of corners from 3rd gear into 4th. Runs great thank you for this help. Hope you have a Merry Christmas and a prosperous New Year.

Glad to here it! Same for you.


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