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XR400 Jetting Recommendations

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Good Evening. Yup another Carb Question thread. Hopefully if free time allows this weekend, I will be pulling the carb to get a baseline on what is in there from the PO as he was of age and couldn’t remember. I did and am still doing research on jetting to get comfortable with the process to not blow things up.

I have YT videos posted in my cmbthumper XR400 thread on my first shakedown run after purchase. No real cold or warm starting issues, hesitation at any throttle input or popping on Decel. Couldn’t pull the plug to check color as the PO did not have one. I ordered one and it should be here this week. Don’t have experience on the XR400 or much air cooled motors but my only concern was the heat generated. Temp gun after first 10mi run was 210-220deg +/- 5deg on the lower cases and 245-260deg +/- 5deg on any part of the head.

This has been asked a million times and answered in a million different ways. Would appreciate any baseline starting points on jetting. From my research there is always the "What Bike, What Mods have you Done" questions from the experienced people trying to help. I am slowly learning about my bike, terminology, what certains are, what and why they do the things they do. So, i gathered as much info as i could to help you help me.

00 Honda XR400R CA Model:

E-Start (Not rubbing it in but might be a factor)

Stock Keihin 36mm Carb (Believe it is the PDK1E. Not sure yet how to tell)

Stock Exhaust with Gordons Mod #1 - 3 Holes in Muffler Baffle

** Stock Header with Gordons Mod #2 - Header Inlet Ground to 18mm

Gordons Mod #3 - Snorkel Removed & Uni Air Filter plus Cage

Float Level to 14.5mm-19mm

Stock Needle 3rd Groove from Top (Believe it is the 06012-KCY-771. Not sure how to tell yet)

XR’s Only Choke Plate

14/48 Gearing

Me?? I am a sit-down type of rider that likes to explore, stop and look at things, take in the views for pics and just plop around. I ride like I have no real purpose or destination. I will say that on a very rare occasion when the terrain opens I like to pretend I am racing for overall time. Until I gain some more jetting knowledge, I would rather the jetting be on the safe rich side and have no problem sacrificing some performance and/or response initially.

Ride from my home Ramona, CA 1625ft ASL to 6200ft ASL – 65-95Deg AT – Humidity 0-10%

85% of my riding will be from my house (See below for remaining 15%)

These are the Jetting recommendations I could find that seemed reasonable but not sure which to start with.

1.      Recommended 700 to 3200ft ASL - 160main - #60pilot - Needle Clip in 3rd Position-Recommended Pilot A/F Screw 2.5+/-3/4turn Turns Out

2.      Recommended 3000 to 7500ft ASL - 160main - #62pilot - Needle Clip in 3rd Position-Recommended Pilot A/F Screw 2.5+/-3/4turn Turns Out

3.      Recommended 3600 to 7000ft ASL - 150main - #55pilot - Needle Clip in 3rd Position-Recommended Pilot A/F Screw 2.5+/-3/4turn Turns Out

4.      Recommended 4500 to 11000ft ASL - 155main - #52pilot - Needle Clip in 2nd Position-Recommended Pilot A/F Screw 2.5+/-3/4turn Turns Out

5.      Recommended 5000 to 12000ft ASL - 155main - #58pilot - Needle Clip in 2nd Position-Recommended Pilot A/F Screw 2.5+/-3/4turn Turns Out

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For the remaining 15% of my riding, I will visit these places maybe 3 or 4 times a year for vacation

** Would like and appreciate any general recommendations to Jet for Big Bear, CA – 6750ft ASL to 8500ft ASL – 65-95Deg AT – Humidity less than 15%

** Would like and appreciate any general recommendations to Jet for Mammoth Lakes, CA – 7880ft ASL to 10000ft ASL – 65-85Deg AT – Humidity less than 15%

 

I appreciate any and all help,

Mike

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In my experience, all those jetting combos are off. Too rich, especially 4 and 5. To stay within reasonably acceptable/optimal jetting for an elevation, you should rejet for every 3000'-3500' change in elevation.

For your mods, setup and home elevation I'd go with 158/58. It will rich at 6200' but that's better than too lean. You could try jetting for the middle, between home and that 6200' with a 155/55 and it will run better at 6200' but might be lean around home. Given the type rider you say you are, not riding on the main(3/4-full throttle), you could run 158/58 and drop the needle to the 2nd from top. That would allow the engine to run not quite so rich as you go up in elevation since it sounds like you'll spend most of the time in the needles throttle range. Then lean the fuel screw to adjust for off idle response- up to 1/4 throttle, as you need to when going up in elevation.

Trying to come up with one jetting combo for a wide elevation range of 1625'-6200' without being too rich at one end and too lean for the other is difficult to the point of being unrealistic IMO. Especially for a 7000' change in elevation range as in example 4 and 5. If that's what you want to do, it's just going to take some jetting experimenting on your part to see what you can get away with.

If you use my jetting rule of thumb, change jetting for every 3000'-3500' change in elevation by 1 jet size, you can figure what will be close for any elevation, starting with your home elevations jetting.

I live at 3600', have all of your mods and run 155/55 up to around 7000', depending on weather conditions, before thinking about rejetting. If I know my riding is going to be spent at and above 10k, I run 148/48, so you can see, with our mods, the jetting in your example 5 is way to rich for that elevation.

One other thing. Calif. models have a different needle than the other 49 states. When you get your carb apart, check your needle code. It will be stamped. A16 is Calif. and A16A is everyone else. The Calif. needle is leaner, so your 3rd from top position is leaner than my 49 state needles 3rd from top position.

Hope this helps.

Edited by Trailryder42
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Trailryder42,

Awesome,Awesome, Awesome. Thank you for the response. Going to grab a few cups of coffee and read this a few times.

On a side note. I looked on Google Earth at my riding area. 85% of the time will be max 4200ft. The 6200ft I mentioned was our highest mountain that I would visit but that is peak and the road is 5900-6000ft. For Elevation I am just going to make the numbers even to calculate the jets per your very understandable 3000-3500ft Elevation changes.

From what I gather during my research is Of course the Main, Pilot and AF screw will be the changed items. I have no problem experimenting for my bikes particular needs. A trail side or campsite change of those three would be no problem but my question is on the needle clip. Even if I have to get more on the throttle, is it better to have the Needle clip in POS 3 and change the other 3 items more frequently as it is easier to do than to not have to pull the carb on the side of the road so to speak.

thank you again for the response

Mike

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I'm not sure how much leaner the CA needle is compared to the A16A needle. Whether it's a clip, half clip, etc.. Most of the jetting suggestions you'll get are based folks experience with the A16A needle. A lot of CA folks will upgrade to the A16A as part of doing all the engine, exhaust and airbox mods like yours has. 16012-KCY-681NEEDLE SET, JET $26.08

Over the years, I've found mine runs/performs better at 10k and over when I drop the needle to 2nd from top. Otherwise, I leave it in the 3rd position all the time. If I leave it in 3rd for those high elevations, it still runs fine, just a little blubbery. I don't like that tho, which is why I'll take the time to retune whereas someone else might ride it as is.

Like I said earlier, for a wide range of elevation I may expect to be encountering, I'll jet the pilot in such a way that I can adjust rich/lean with the fuel screw as elevation changes start to effect throttle response. The main can be swapped on the trail by loosening the carb clamps, rotating the carb and removing the bowl plug, a 5 minute job.

Once you determine what runs good for you at different elevations and conditions, write them down in your shop manual. Until then, carry a selection of main/pilot jets and related tools with you.

I've had my XR for 18 years. Any more, it seems like the only tools I carry are a plug wrench and a 2 stroke spark plug.

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