XR400R Carburetor Jetting

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XR400R Carburetor Jetting

Post by 4Strokes » Mon Jun 06, 2016 2:53 pm

Topic: UPDATE-XR400 Jetting at 6,500 ft?
Author: xr400jm
Posted: 10/27/2003 8:40:04 PM

I live near Colo. Spgs. at about 6,500 ft. I bought a '96 XR 400 and knew right away it ran lean. I jetted it to the specs a local Honda service Dept. gave me. It does run better, but it's hard to start when cold! If I turn in the idle speed screw a few turns, it'll start, but once it warms up that idle becomes way too fast. I know fundamentally how the tapered needle works, but do you think the position of it is the problem? It's the stock needle, I believe in the 2nd notch from the top. ANY suggestions? Any FULL set-up ideas?Thanks fellas!

UPDATE- I'm currently running a 142 main jet, 65 pilot, and stock needle in the 2nd position. I turned the fuel screw and got almost 4 full turns. Sparkplug is slightly black around the edges, but burning clean in the center. Honda also recommended a needle, P/N: 16012-NKK-000. In the third position.
Bigger pilot, and new needle? Thanks

Reply by Sergeant Tork on 10/27/2003 9:00:35 PM
Are you sure you were running lean? As altitude increases, the air is thinner (less oxygen). Less air equals a richer condition. However, if your dealer gave you an idea of what jets to use and if it runs OK then you may be in the ballpark. You can check the temperature of the engine (high temp = lean) and do a spark plug reading to fine tune it.

Anyway, I think you should concentrate on the pilot system. If needed you could go up one size on the pilot jet, but the first thing you should do is check to see where the fuel screw is adjusted. The fuel screw is located on the bottom front of the carb and is basically that upside down screw. Turn it in clockwise a half turn at a time carefully counting how many turns it takes before seating (lightly but firmly...don't wrench on it). Proper initial setting is 1 and 3/4 turns out. Turning it out counterclockwise in 1/4 increments will enrichen the pilot system. If your pilot system is lean, turning out the screw can make the bike easier to start. If you need to turn it more than 3 turns out you may need to go to the next higher pilot jet.

Reply by Jonathan on 10/27/2003 9:10:06 PM
xr400jm, I recall in 1998, cycle world ran a comparison test of several popular mid sized dirt bikes. while the xr400r acquitted itself well in the test, the writer emphasized that Honda had changed the carburetion in the 98 model year so as to help high altitude running. my service manual (for xr400r) lists a PDK1A carb for 96 & 97 year models and a PDK1C for 98, 99 & 00 models (PDK1C may also apply to 01, 02 & 03 yet my manual is a 1996 - 2000 edition). this chapter also indicates that stock jetting differs between the two carbs with the 96 & 97 models using 162/62 as main/pilot yet 98, 99 & 00 models using 142/52 (again, as stock). I suspect the needle, needle jet, and carb slide also differ, PDK1A vs. PDK1C. I wish I could be more helpful; living near Taos, NM, I too have struggled with jetting for my 00 model xr400r; for the record, 155/55 works for me (k & n air filter, no snorkel, baja designs exhaust tip, all at 7000 ft). here's something that might help, that is, hard starting sometimes means a larger pilot jet (and/or opening the fuel screw further, e.g., half turn more, counter clockwise) is needed. good luck with your xr, Jonathan

Reply by damone on 10/31/2003 11:37:52 AM
I have to turn the idol screw out for all cold starts. Once it's warm I adjust the idle to a good level. No big deal just a part of the procedure.

Reply by NorCAL XR on 11/01/2003 12:21:21 PM
The dual tapered needle comes stock on the 49-state XR. If you have a California model, you have a single taper needle. So if your bike wasn't manufactured for CA, then don't switch out the needle. If you have the needle out of the carb, the dual taper is visible. The first taper is from the tip and quickly has a step in the length of the needle. The purpose of a single taper is for CA emissions. It hinders the jetting from richining up at higher throttle positions. If the needle doesn't taper, a lesser amount of fuel will pass by through the main jet at any given throttle position.

Reply by whyr on 11/06/2003 05:41:44 AM
My 2001 XR400R and I spend most our my time riding above 5000ft in and around Colorado Springs. Recently, I also rode a hares scrambles in Denver, which was 2 hours of WFO. After a recent Moab trip and after the Berthoud hare scrambles, I checked the plug and it was a nice gray over the whole spark plug. I would say that that is pretty good. Currently, my main is a 138 and the pilot is a 55. I remember handling the needle but I don't recall what I did.

Question: I bought the bike used and was wondering how to tell if its from California? What would different if anything?

Reply by Jonathan on 11/06/2003 08:45:50 AM
whyr, one readily visible difference between California xr400r's and 49 staters is the crankcase vent arrangement. my 49 state model has an uncomplicated rubber tube exiting the crankcase, just aft of the cylinder. the tube quickly goes into a "T" fitting with one end heading south, terminating just below the bike's bottom with a "duck bill" like flapper valve: the other tube exiting from the "t" goes up and makes a u-turn by the top of the rear shock and simply ends (that is, open tube is "dangling down": being a little compulsive, I've fixed a small k & n crankcase filter there on my bike). the California models start with the crankcase vent tube exiting just aft of the cylinder (same as 49 staters, so far) yet then goes into a "breather separator" (small plastic box/fitting): from there, one tube goes south, ending just below the motor (again, similar to 49 staters, so far) yet instead of a one way duck bill-like fitting on the end, it has a screw off cap. a major difference is that the second tube (leaving the breather separator) goes directly into the intake manifold (or more plainly put, the large diameter rubber connecting the carb to the cylinder head). as California is often out in front of the rest of the country on many trends (air pollution, for example), the extra efforts to keep crankcase oil vapors from getting into the atmosphere sort of makes sense. it's too bad that a 24 cubic inch motor (400 cc) is subject to this; common sense tells me that air pollution controls are more important on 400 cubic inch engines. say, as a gas gas pro, does that get you free rides on those awesomely fast gas gas 2 stroke dirt bikes or those steady, plonking gas gas 2 stroke trials rides ? either way, i'm pea green with envy. adios, jonnie tree bike

Reply by Jonathan on 11/06/2003 08:51:38 AM
oops ! reading the above, i see a screwed up slightly. the second tube for the California bikes goes into the large diameter rubber tube connecting the air filter to the carb. if i were perfect, i'd be scott summers ! jonnietreebike

Reply by whyr on 11/06/2003 09:34:11 AM
Thanks for the update. I was just wondering why my jetting was so different from riders engines. I thought maybe it was the bike. I'm not a "Pro". The name of the bike is a Gas Gas Pro, but I do get rides on the newest Gas Gas bikes cuz the dealer here is so good. Thanks for your attention to detail.

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