What size jets on an XR400 w/ hi-flow setup?

Hey,

Start off richer first, then work your way to leaner. The 160/60 jets are a good starting point, if not close to perfect at our elevation. Just try it and see for yourself, read your plug and adjust the pilot screw. You can also change your needle clip position which affects more of the midrange. Furthermore, your ideal jetting may be a 162/60, or 160/62, or even a 162/58 or something. It's all trial and error, but I can almost guarantee that the 160/60 jets will be very close to where you want it. Good luck.

Actually, my bike came with the 162/62 jets. With the richer pilot it started easier cold, but flooded out easier. The 60 pilot made it harder to start cold, but throttle response was much better, and the bike started easy hot, and almost never flooded out. However, with you coming up from a much leaner pilot, the richer 60 pilot should definitely help you with cold starting. One trick a guy taught me, was to tip the bike over, to flood the carb, when starting cold. It helps get alot of gas to the cylinder quick. It took only 2-3 kicks compared to 7 or 8 after trying the trick. Good luck.

Hey,
NO, do NOT even think of using needle nose pliers! Jets use a standard metric hex, I don't recall which, maybe 6mm or something.

1) Remove the seat and side covers, and gas tank. Unbolt the exhaust from the rear subframe, 2 spots, unbolt subframe from the frame (down by foot pegs), Loosen airboot from carb intake and then just rotate the rear subframe up to point to the sky. Pull out your airbox while you are at it and give it a good scrub down, in and out, in the airboot, and clean your filter. You may want to support your exhaust pipe so it doesn't hang there and damage your header.

2) Now, remove the throttle cables and loosen the carb from the intake manifold. Pull the carb out the rear, to the right of the shock. Cover that intake manifold so nothing gets into the engine with the carb removed, but don't forget to uncover it when reinstalling the carb!

3) Watch out gas will spill out the carb! Flip the carb over, remove 4 phillips screws and the bowl comes right off. Watch how the plastic baffle thingy inside goes, then pull it out, if it didn't already fall off. Do not mess with the float, it doesn't need to come out. But you can check the float level if your Clymer manual shows you how. Now, you will see long brass hex thingys sticking up, one in the middle(main jet) and one up front(pilot jet). Unscrew them. Use carb cleaner and spray all over, in the holes, clean out any junk in the bowl of the carb. Now install the new jets, tighten them up until they LIGHTLY seat, do not over torque them, put the plastic baffle thingy back in on the main jet, and reinstall the bowl.

4) Now, reinstall the carb and throttle cables, and put everything back together. Route all your carb drain lines, don't forget to put the gas line back on when you put on the tank, and triple check a good fit on the intake manifold and airboot to the carb, you don't want any air leaks. Also, triple check your thottle operation. Make sure there is a bit of free play, and that the throttle snaps back closed, turn your wheel from side to side extremes to make sure there is no binding in the cables.

You will need metric sockets, metric allen wrenches, phillips screwdriver, carb cleaner, pliers (for your gas line ONLY), and alot of patience. You really should get a torque wrench also, but you can get away without it. Keep all your screws and hardware in little groups so you know what goes where, and clean everything. Don't be scared, it's not that difficult. Just be very patient and careful and pay attention. Good luck, ask questions if you don't understand.

I replace the jets with the carb still on the bike. Use a short phillips screwdriver and remove the bowl screws. Replace these screws with allen head screws which are easier to install. The jets may now be easily replaced. As snaggle mentioned the plastic slosh plate must be aligned properly when you replace the bowl. It will stay put on the main jet upon reassembly. With some practice the jets may be replaced in less than five minutes.
I also installed a mikuni pumper from XR's Only last friday and am amazed at the throttle response. The front may be easlily lofted around logs and rocks on tight trails.

Hey Ud!

Did you get the Mikuni 36 pumper? For an XR400? If so, any "ah-ha's" to be aware of? Did you get the throttle/cable assembly as well?

Thanks! E-T

Hey,
I bought my Mikuni pumper from XR's Only. It did come with longer throttle cables. Also, a set of richer and leaner mains/pilots for tunability. However, mine seems to be nearly perfect the way they set it up.

The fit was perfect, they machine their own bushings to fit the intake manifold, everything went together like it was the stock carb. The carb makes the power everywhere, very smooth, with a mean lower-mid to upper-mid pull. The power is crisp and clean, and the motor builds revs up faster than ever before. I'm very pleased with the carb, I only wish I would have gotten it a long time ago.

damn.... I was afaid of that. (big sigh...)
Guess I'll be writing a check tomorrow.... (grin)

Thanks, Snag! - E-Ticket

snaggle couldn't have said it better, The Mikuni is the best change I have done to the bike. Much easier starting and the low to mid stumble is virtually eliminated. The jetting seems to be perfect as received. I did have to adjust the pilot screw some but it was very minor.

Hey,
Xr's Only had it in stock and got it too me within the week. It is expensive, but well worth it. One thing I never did do was suspension work. I recently bought a 2000 XR650R, and other than the huge power difference, the biggest difference is the superior suspension. For a 300lb. bike, the XR650 handles better than the 400 and feels tons better on roots and such. So, for the money, you might also consider some suspension work on your 400, especially on the forks. You will be happy either way, but as they say, power is nothing without control.

Hey,
I'm glad you had good luck. Now, you need to play with your pilot screw, on the bottom of your carb, closest to the engine. First, while the motor is off, count the turns to screw the pilot screw in (righty-tighty, lefty-loosy) until it lightly seats. Remember this position, probably close to 2-2 1/2 turns out from fully closed. Now return the pilot screw to the original position.

In is leaner, out is richer. While the engine is fully warmed up and running, there should be spots in both directions where the motor runs poorly. The ideal position is exactly between the two. For example, if the bike runs bad at 1 turn out, and again at 3 turns out, then you want to be at 2 turns out. Unfortunately, it isn't always that easy. You can also listen to the idle speed. As you turn the pilot screw in and out, listen for the spot where the motor idles the fastest, and sounds the cleanest/best. This should be very close to your best position. Now, since the idle is running higher, readjust your idle screw down to a good idle speed.

If, you can turn the screw all the way until it seats, without causing the motor to run poorly, then your 60 pilot is too rich, try a 58. At the same time, if your motor runs the best at 3 turns out or more then the 60 pilot is too lean, try a 62. Again, if you motor runs poorly close to fully closed, and runs poorly out past 3 turns or more, then your 60 pilot should be nearly perfect (standard position is about 2 1/4, +/- 1/2 or so).

To add to the above paragraph, I've heard that even though your needle clip position primarily affects the range from 1/4 to 3/4 throttle, it still affects the other circuits, by smaller amounts. For example, if your 60 pilot is pretty darn close, but you think it might be a tad lean, then lower the clip on your needle one position to a richer setting ( or raise the needle, same thing, depending on whether you are looking at the clip or the needle). Richening the needle should also richen up your main and pilot jets a tad. At the same time, if your 160/60 seems a bit too rich, leaning the needle a position might be better.

To test for your main jet, install a new plug. Go riding and open her up to full throttle. Clutch, chop the throttle off, and hit the kill switch all at the same time, do not let the motor slow back down to idle. Pull the plug and see what color it is, white/light grey is lean, dark brown/black is rich. You want it to be a medium brownish/grey, kinda like Nestle Quick, or Cocoa powder. Again, changing the needle postion may help a bit, but a 162, or 158 main jet may be in order.

Carb tuning is quite complicated, even with a good starting place, it is a trial and error situation. Always remember that a bit richer is always better than a bit leaner, and only change and test one thing at a time. Keep in mind, your aircooled motor will run hot, especially in the Texas summers, so richer is definitely better (as long as it isn't blubbery and unresponsive).

One more thing, if the exhaust backfires and/or pops kinda like a Harley when you let off the throttle, then you are a bit lean on the bottom. Adjusting your pilot screw and/or needle to a richer setting should nearly get rid of it. However, with a high flow exhaust, you may not ever totally get rid of it, just minimize it.

Good luck, and enjoy your bike. Change the oil/oil filter/air filter/ and clean the oil strainer screen very often. Don't forget about keeping those valves adjusted. I really need to stop writing these darn books, sometimes I confuse myself. Ask questions if needed.

rejetting XR400R

The XR 400 is the best bike I have ever owned, except for cold starts and engine stalls. I also have the Exhaust diffuser and snorkle out of my bike with no jetting changes. Think I'll try the 60/160 jetting set up. This will richen the Ari/Fuel mixture right?


PS Any of you Texas guys want ride let me know, I know of many good places in Oklahoma, Arkansas, Louisiana, and Texas. This is a a great site thanks

I rode my xr4 today, first time in over a month. This bike really rips, climbs like a billy goat, uphill wheelies etc. I never had luck with the 60,160 setup, for my xr use 55,155,needle #3. Gonna lean it out some more when it warms up.

Mountain,
There ia a place in Austin called City Park, this is a desecent place. Between Houston and Conroe you can ride the Sam Houston National Forest. There are probably close to 80 miles a trails there but there pretty much all flat, but beautiful scenery. If you can get away to North Texas I can give you direction to some other very good places. I plan to change my jetting soon hope mine works as well as yours does. Did your local Honda dealer have them in stock?