Carb Questions

2 replies to this topic

Posted September 25, 2011 - 02:36 PM


Got a 98 YZ400F thats stock. I'm going back throught the carb and wondering if there is anything to change to help it run even better. I've done the collar on the accel pump rod to help with bog. That helped get rid of some of it. It starts well and idles well. Does pop on decel just a bit which I believe is OK. I've changed the fuel mixture screw which is out 3 full turns. Added a quick shot accel bowl too. Jetting is all stock. I have stock exhaust but I shortened it about 3 inches (just looks) and repacked it. Thats all I've done and feel maybe I have been counter productive. Just looking for direction like different accel pump diaphram for a little more fuel. Maybe jetting change. Just open to options. Thanks for your time and please let me know if there is anymore info needed.

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  • ttr250dude

Posted September 27, 2011 - 01:29 AM


If you have your fuel screw 3 turns out, it means your pilot jet is too small. Go up 1 size on your pilot jet, turn the fuel screw in a bit, and go from there.

Here's a link to the jetting database for your bike. Spend some time reading the posts to get a good starting point.


Posted September 29, 2011 - 05:08 AM


Thanks for the info. I'm going to take your advise and start there. Just waiting on parts to show up. Thanks for your time.

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