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xr400 carb problem

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This is my first time to ask a question. I hope it is right.

I have a 2000 xr400 that is difficult to start. Isn't the engine supposed to fast idle with the choke on. All my old xrs would fast idle. This one just barely idles. Any touch of the throttle will kill it. The dealer told me there was a idle enrichment valve, but I can't find it. The carb has a 132 main jet and a 52 pilot. My riding altitude is usually 7000 to 11000 ft.

Thanks for any advice!

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First off, your jetting seems off to me for those elevations. Your pilot is that of a bike with intake and exhaust mods but the main is that you might find with a bike in stock configuration.

You need to tell us what intake and exhaust mods are done. Such as the snorkle being pulled, stock or other air filter; stock, modified stock or other exhaust?

The carb has an idle speed knob. It's that black knob. You may be running your idle too low for the bike to start. Helps to give it a 1/2 a turn or so clockwise before starting.

Make sure you have the position of the choke right in your head. All the way down is choke off. All the way up on the lever is choke full on.

There's not an idle enrichment valve/circuit on the stock carb. It's just simple choke flap.

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Just about every XR I have owned needed the idle speed adjuster set up a turn or so for cold starting. When the engine warms up, turn it back down.

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has your bike been jetted for the altitude? I agree that the pilot jet is pretty big for a stock bike and I bet you can almost start it with no choke because it is so large.

I've played around with my carb jettings and finally bought a pumper carb from XR's Only and it has totally changed the bike. It starts right up whether it's cold or I just laid it down. Before when I would crash, it would take me forever to get the bike started but now, no worries. It has really made the bike much more ridable and the ease with which it starts now is fantastic. It cost around $350 and it took me a few years to come around to doing it but I wish I had done it sooner. It's easy to install as well. As we get older, we have less and less kicks left us in so you gotta do what you can to save em' :worthy:

Patrick...

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This is my first time to ask a question. I hope it is right.

I have a 2000 xr400 that is difficult to start. Isn't the engine supposed to fast idle with the choke on. All my old xrs would fast idle. This one just barely idles. Any touch of the throttle will kill it. The dealer told me there was a idle enrichment valve, but I can't find it. The carb has a 132 main jet and a 52 pilot. My riding altitude is usually 7000 to 11000 ft.

Thanks for any advice!

According to my manual and the dealer the stock main is a 142 and the pilot is a 52, so ir has been leaned out some. The snorkle has been removed, stock air filter. The exhaust is stock with 8 holes drilled around the spark arrester. That is all I know that has been done to it.

The bike runs really good, just hard to start.

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The stock air filter and cage is a bottleneck for the way the rest of the system is configured. You should consider putting in a UNI filter that comes with its own cage.

Then bump up that main to a 150. Drop the needle to the 2nd from top clip position.

I think 8 holes in the arrestor is overkill. I'd plug half of them. If they're 1/4" holes, you can plug them with 1/4" x 20 set screws.

I think the 52 pilot is too rich for your current configuration for those elevations. After doing the UNI filter, a 52 would be closer to what it should be, tho still a little rich once you get up around 9k from my experience. I run a 50 up that high.

The snorkle has been removed, stock air filter. The exhaust is stock with 8 holes drilled around the spark arrester. That is all I know that has been done to it.

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There's not an idle enrichment valve/circuit on the stock carb. It's just simple choke flap.

I agree that the idle speed adjust (throttle stop) might be off.

There IS a pilot screw to adjust the idle mixture on the stock carb of XR400 from 96 on. It is located on the front underside of the carb just under the boot that attaches the carb to the head. The manual says to "turn the pilot screw clockwise until it seats lightly then back it out 2-1/4 turns then with the throttle stop screw set to approx 1300 rpm, adjust the pilot screw in or out untul the highest rpm is obtained" I'd bet my old wheel bearings that this will fix the problem.

For all you jet-nazis, your main jet size will have no appreciable affect on idle speed, and your pilot jet would have to be several orders of magnitude wrong before it will completely useless.

Look to see if your float is set to the correct height; too low and the pilot jet will be starved on demand. For this reason (and to offset bogging on hill climbs) you should fit a small piece of fuel pipe to the to pilot jets to extend its reach anyway.

very important: if the new bike has been standing for any length of time the fuel may have gone off. Drain the tank and the carb bowl (there is a drain plug) and put in new fuel.

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Good on you for bringing that up Meatbomb. There I go again, assuming the poster knew of the fuel screw. Got hung up on the dealer telling him there was a "valve".

There IS a pilot screw to adjust the idle mixture on the stock carb of XR400 It is located on the front underside of the carb just under the boot that attaches the carb to the head. .

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Just about every XR I have owned needed the idle speed adjuster set up a turn or so for cold starting. When the engine warms up, turn it back down.

Christ, I really really wish I'd heard that before. Really:banghead:

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Thanks everyone for suggestions and advice. If I go to a 152 main jet, isnt that going to really richen it up too much for this altitude? I am going to clean it, set the float and put it back together. I will let you know. Again THANKS

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Yes, "if" you keep the stock air filter and cage.

If you install the freer flowing UNI unit, to match what the rest of the intake tract (with the snorkle removal), and modded exhaust are capable of flowing, then the 152 will be very close. May take a 150, especially above 9k feet.

If I go to a 152 main jet, isnt that going to really richen it up too much for this altitude?

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Yes, "if" you keep the stock air filter and cage.

If you install the freer flowing UNI unit, to match what the rest of the intake tract (with the snorkle removal), and modded exhaust are capable of flowing, then the 152 will be very close. May take a 150, especially above 9k feet.

That makes sense. I will go to the bigger jet when I replace the air filter.

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This is an old thread, but might as well prove that I did search for the answer before popping off a stupid jetting question. Parts guy recommended a 132 main jet. I have a stock exhaust and the snorkel removed. Live at around 6000 feet and ride up 9000 regularly. Is this too tiny a jet? Is this for the XR250?

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This is an old thread, but might as well prove that I did search for the answer before popping off a stupid jetting question. Parts guy recommended a 132 main jet. I have a stock exhaust and the snorkel removed. Live at around 6000 feet and ride up 9000 regularly. Is this too tiny a jet? Is this for the XR250?

the title of the thread is XR400 carb problem. so jet sizes mentioned in this thread would not be applicable to your situation.

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Yes, 132 would be too small. For 6k-9k elevation you're looking at a range of about 148-150 for the main. When you get up that high, the stock carb response benefits from dropping the needle to 2nd clip position from top also.

Edited by Trailryder42

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I just checked in mine currently is a 142. Maybe mine is not running rich at all. I have not checked the needle position. I'll report back in time. Thank you.

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Your snorkle is removed and exhaust is still stock. Still running stock air filter and cage?

The jetting I gave is for snorkle removed, better flowing air filter like the UNI and the exhaust tip with Gordon Mod.

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Regarding holes drilled (Gordon Mod) - 4 holes worked pretty good for me. I went up to 6 at one point and it ran like shit. Even with a Mikuni pumper carb. I think over 4 drilled is about the point of diminishing returns for that mod. A bunch of little holes will not flow as well as 1 outlet at the equal amount of area. Plug up half of them or switch to a 96-97 spark arrestor minus the removable pea shooter. Just my 2 cents. :thumbsup:

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