i just put a powroll big bore kit on my cousin's 250ex and we can't seem to get it running right. first off when cold it will NOT idle but after it gets hot it idles wat too high. second when you let off the gas it backfires and shoots a long flame out of the pipe. i have tried to get this thing running right for a week now and i'm just stumped so please help

 

hondaguy13,


Your jetting is way off. Before you go any further check your see what color your plug is. Look at the plug readings below.

You will need to go up on your pilot(slow jet)for idle, main jet, and possibly change out your jet needle.

Also make sure to take plug readings after each adjustment. You do not want a lean condition.
Once you get it your quad going, make sure to take plug readings for the circuits marked with *.

White plug = Lean
Black plug = Rich
Tan to Brown = Right on

Here are your carb circuits and what they operate.

Carburetor Circuits
*Air Screw = Idle to 1/8 Throttle
*The Pilot (Slow Jet) = 1/8 to 1/4 Throttle
The slide valve = 1/8 to 1/2 Throttle (Rarely ever replaced)
*Jet needle = 1/4 to 3/4 Throttle
*Main Jet = 3/4 to Full Throttle

Good luck.

Hope this helps.

SB.

 

well the thing i don't get is the plug is black which means it is rich right? well i would assume putting this big bore on it would make it lean

 

You are running rich. The best place to start with jetting is to look at some web sites that get into jetting principals. I could write up a jet how to for you but I may forget something important. The list of items you will need are some new plugs for testing, a clean air filter, and some new jets. Here are a couple of sites on jetting. Also while your at the Honda dealer talk to them about your condition so they can set you up with the proper jets.


Jetting 101

Carb tuning

Hope this helps. But take your time and be patient. It can be time consuming but you will learn alot.

SB.

 

Jetting the 250ex is tricky, even with just a slip on and new airfilter. Don't open your airbox, vents should do it. The 250ex doesn't like alot of air. What main did you put in it? I put a Megamax II and Uni filter on my wife's and added 4 airbox vents and only went up one on the main. I adjusted the air/fuel screw about half a turn and it's good.