2000 400ex: LRD pipe(complete), uni filter,octane boost additive.
No jets have been changed and air box lid is ON.
LRD says to run airbox lid on if no jets will be changed.
PROBLEM: My 400ex cutts out at full throttle, upper RPM ranges, in all gears. It does not cut out when the trottle is instantly hit wide open.
Example: was wheelying in 2nd gear on pavement, smoothly pumping throttle to keep front up and stay at low speed. Went about 40 yards and suddenly it had a cutting out affect and power was lost. let off throttle and just took off again like it never happened. It will not die when this happens and again it is only at full throttle in the upper RPM range. I know it isn't the rev limiter, because I've never hit it and I'm not running the motor any harder. Could this be the octane additive?

 

The cutting out at wide-open-throttle could be a rich condition even though you haven't changed the main jet, and my first thought is that the fuel additive has raised the octane level and is making it run rich, which more often than not is most noticeable at high rpm's. Before I'd do anything else, drain the tank and run it on a tankful of good quality gas (I run 92 octane myself) and see what happens.

 

The cutting out at wide-open-throttle could be a rich condition even though you haven't changed the main jet, and my first thought is that the fuel additive has raised the octane level and is making it run rich, which more often than not is most noticeable at high rpm's. Before I'd do anything else, drain the tank and run it on a tankful of good quality gas (I run 92 octane myself) and see what happens.

 

2000_Warrior, Thanks for your input, I sure hope you are right about the octane boost, because If it isn't that may mean a mechanic bill. I will drain it and refill with pump gas asap. I can't walk right now do to wrecking my 400ex this past Saturday, but I should be able to in a week or so I hope!

 

First, my resume: I build Hi-Perf H-D motors (106"+) and have developed a carb kit for the Keihin carb for these monsters. I have applied the same technology to the smaller 4-stroke motor and Keihen carb. What I have found to work the best on a slightly hopped up 400EX follows. Since you have changed the exhaust (output) you need to change the intake (input). You already have purchased a top-of-the-line exhaust, but you have not matched the flow characteristics with any real modifications to the airbox. You are going to need to either run with no airbox lid and jump up to about a #165 main or you can drill 12-1 inch holes in the lid and install filters in it and jump up to a #160 main jet. This is the setup I am running in my 400EX (used for sand drags--top end all the time). I even run without the 12 filters in the lid using just the plastic mesh screen that holds them in place. If you are concerned with sand, get an outerwear. Also, you should run a #40 low speed jet and turn the air/fuel screw out 3.5 turns from bottom. When you have done this, get yourself a XR250 CDI (same as White Bros. but about $25 cheaper). I am assuming that Purcell, OK is under 3000 ft. elev. Your problem is a lean main, not a rich one! If you go leaner you could burn up that motor! Also, do not use octane booster unless you are experiencing detonation (pinging). Since you are running the stock piston and head gasket, you do not anything higher octane than premium pump fuel. One more note: changing the main jet on the 4X is really easy, all you need is a 17mm wrench and a 7 or 8mm socket (I can't remember which) to do it. Leave the carb on the bike and get to it from the bottom of the float bowl. DON'T FORGET TO TURN OFF THE GAS!!!

 

I must say I agree with Feara400. With a pipe and no jet or air box mods you are running very lean. I have a 99 400ex with an E-series pipe and 165 main jet and run the stock filter with the air box lid off and I've never had a problem.

A question for feara400. I've heard about using the xr250 CDI. Do you know if it advances the timing like the WB's one does? Thanks in advance.

Ride Hard
Chet

 

White Bros. is not a manufacturer of ignitions (or of just about any other part they sell). They are buying other companies products and putting their name on the boxes. The WB CDI doesn't even have the WB logo or name on it anywhere. If you compare the dimensions of the WB CDI with a XR250 CDI, they are the same. Also, the same company makes the CDI for both WB and Honda. One can only assume that WB found out that the XR250 CDI would work on the 400EX giving it a more advanced curve and raising the limit 1200rpm. Buy the XR250 CDI and save money!