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Jetting newb needs help! XR400 2001

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I just rejetted to 155/58 on my xr.

Starts, runs good but idles fast with full choke, then I turn down choke to half and it dies.

Fuel mixture screw doesn't seem to help.

I'm guessing from what I'm reading that I have the wrong jets?

What jets should I use? current elevation 2200, I ride up to 6000ish often, not really any lower than 2200, mostly 3000-4000

I drilled my exhaust baffle with 3 1/4" holes and removed snorkel, sporting a uni air filter.

I have jets for main 155 158 160 and for pilot 55 58 60 I think... Wouldn't be a problem to buy some more, what do you guys think? It really is a pain to install these things, removing subframe and carb etc.

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Is my jetting likely too lean or too rich? Btw, corresponding to numbers, does lean refer to a smaller number whereas rich is a larger? Likewise do the numbers correspond to larger diameters inside the jets? And one more thing, is it necessary for the pilot jet to = main - 100 give or take? So like if you had 150 then you use 50 ?

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Just read the jets that were in the carb... not sure if they came stock or not.

The main said 138...?

and the pilot said 52S, kinda confused. Anyway..

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I just rejetted to 155/58 on my xr.

Starts, runs good but idles fast with full choke, then I turn down choke to half and it dies.

Fuel mixture screw doesn't seem to help.

I'm guessing from what I'm reading that I have the wrong jets?

58 pilot sounds about right. Is your airbox snorkle torn out? If not, you may be a little rich. Did you adjust the idle knob? Big black knurled knob on the carb - turn it down to adjust idle speed. It is SOP to turn up the idle to start, then turn down as it warms up.

JayC

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I'm trying to process a lot of thoughts here.

First, did you remove the fuel screw for cleaning that passage? If so, did you reinstall the assembly correctly? The spring goes on the screw first, then the washer, then the o ring. O ring in good shape? If you haven't had it out, do so and clean that passage, making sure to inspect the o ring and reinstall the assembly properly. Set it to an initial position of 2 turns out.

Next, be sure you're using the choke right. All the way up with the lever is full choke. All the way down is choke off. Then see if cleaning the fuel screw passage made a difference in the engine dieing after moving to half choke. If not, turn the black idle speed knob in 1 full turn to raise idle speed. Try again. Keep turning the idle speed knob in a little at a time until you can move the choke to mid without the engine dieing.

If that works and you can keep it idling on its own after warming up with choke off, then try to fine tune the fuel screw.

For your mods and elevation I think a 58 pilot may be too rich by 1 size. That is, if everything else is working right and you have no air leaks.

Replace the phillips head float bowl screws with allen head screws. It's easy enough to just loosen the carb clamps and swivel the carb to one side or the other to get the bowl off without needing to remove the whole carb.

I just rejetted to 155/58 on my xr.

Starts, runs good but idles fast with full choke, then I turn down choke to half and it dies.

Fuel mixture screw doesn't seem to help.

I'm guessing from what I'm reading that I have the wrong jets?

What jets should I use? current elevation 2200, I ride up to 6000ish often, not really any lower than 2200, mostly 3000-4000

I drilled my exhaust baffle with 3 1/4" holes and removed snorkel, sporting a uni air filter.

I have jets for main 155 158 160 and for pilot 55 58 60 I think... Wouldn't be a problem to buy some more, what do you guys think? It really is a pain to install these things, removing subframe and carb etc.

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I'm trying to process a lot of thoughts here.

First, did you remove the fuel screw for cleaning that passage? If so, did you reinstall the assembly correctly? The spring goes on the screw first, then the washer, then the o ring. O ring in good shape? If you haven't had it out, do so and clean that passage, making sure to inspect the o ring and reinstall the assembly properly. Set it to an initial position of 2 turns out.

Next, be sure you're using the choke right. All the way up with the lever is full choke. All the way down is choke off. Then see if cleaning the fuel screw passage made a difference in the engine dieing after moving to half choke. If not, turn the black idle speed knob in 1 full turn to raise idle speed. Try again. Keep turning the idle speed knob in a little at a time until you can move the choke to mid without the engine dieing.

If that works and you can keep it idling on its own after warming up with choke off, then try to fine tune the fuel screw.

For your mods and elevation I think a 58 pilot may be too rich by 1 size. That is, if everything else is working right and you have no air leaks.

Replace the phillips head float bowl screws with allen head screws. It's easy enough to just loosen the carb clamps and swivel the carb to one side or the other to get the bowl off without needing to remove the whole carb.

Thanks for the tip on removing the bowl.

Yeah I thoroughly cleaned pilot screw and disassembled / assembled correctly... I think the problem lies in the jet size maybe, I'm going to try some other sizes when I get more time to work on it, thanks for the response maybe I'll try a leaner one, I'll try playing with the idle knob as well.

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Gordon's Mod's suggest a #60 pilot and a #160 main. I've heard of folks using up to a #165 main.

I think you need larger jets!

Perc

That's what my friend seems to think, I might have to buy some bigger ones! I'll try the ones I got first though, just kinda discouraged at how long it takes.

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58 pilot sounds about right. Is your airbox snorkle torn out? If not, you may be a little rich. Did you adjust the idle knob? Big black knurled knob on the carb - turn it down to adjust idle speed. It is SOP to turn up the idle to start, then turn down as it warms up.

JayC

Ok, I'll try that before anything else, thanks.

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Your fuel screw does nothing and you only drilled 3 holes and added a UNI filter correct? Did you pull the airbox snorkel or gring header welds? If not, I would think 58 would be to rich and you should back it down to 55 and see if you get a response from the fuel screw.

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Your fuel screw does nothing and you only drilled 3 holes and added a UNI filter correct? Did you pull the airbox snorkel or gring header welds? If not, I would think 58 would be to rich and you should back it down to 55 and see if you get a response from the fuel screw.

Yeah I took out the snorkel, I didn't grind the header welds. Should I grind those? Is it worth it?

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I didn't grind the header welds. Should I grind those? Is it worth it?

It depends. Some welds are worse than others. I've seen welds so bad that after cleaning them up, pipe id at the weld was almost doubled.

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Its not hard to take off and check, I checked mine when I was porting the intake and exhaust and they were great, barely any material for me to take off, but like trailryder said I have seen some with a lot of material.

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Yeah I took out the snorkel, I didn't grind the header welds. Should I grind those? Is it worth it?

Not likely, unless the welds are really big and ugly. Even then, it will only help at the highest RPMs. I ground mine, but didn't notice much of a difference - mine weren't that big to begin with though.

JayC

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Hm, thanks for the replies. I'll take a look next time I work on it.

So, in regards to my jetting problem, I have taken note of a few possible problems that I should check for.

-Air leaks inbetween inlet and cylinder head.

-Pilot jet clogging

-Pilot screw clogging / damaged o-ring

-Throttle adjustment?

-idle adjustment

-wrong pilot jet.

I went until about four turns out with the fuel screw, and assuming none of the above were a problem then what I've read suggests that I have the wrong size pilot. Too bad I won't get a chance to work on the bike for a little while because I'm pretty busy this week but I think I've got a pretty good idea of what to check.

If anyone has any other things I should check let me know, also still open to suggestions on which size jetting.

I've heard of people who live near me with removed baffles running up to a 165 main, and 60 or 62 pilot, also heard of people using a 155 main who live near me. It is unclear to me.

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So, in regards to my jetting problem, I have taken note of a few possible problems that I should check for.

-Air leaks inbetween inlet and cylinder head.

-Pilot jet clogging

-Pilot screw clogging / damaged o-ring

-Throttle adjustment?

-idle adjustment

-wrong pilot jet.

I went until about four turns out with the fuel screw, and assuming none of the above were a problem then what I've read suggests that I have the wrong size pilot.

Yes, "assuming none of the above were a problem ". But I still say 60-65 pilot is too rich for your mods and elevation. I say 55, but your current problem doesn't support that. That's why I think there's something else going on.

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This does sound like an air leak... Ya think ? :bonk:

Perc

Easy way to check that? Maybe listening to rpms and spraying carb cleaner around the intake manifold?

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This does sound like an air leak... Ya think ? :bonk:

Perc

Just checked, with the little time that I have, no air leaks.

Black idle knob can turn the idle up, but to achieve running without choke, it is a ridiculously high rpm with the choke on, fuel screw does absolutely nothing, from 1 to 5 turns out.

So, I suppose it's a problem on the inside of the carb, which I kinda figured. Problem is, I won't have time to open it up until next week :smirk: Or xmas eve maybe.

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