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Pilot Jet

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I have a 2003 XR400. It is a California bike, all stock with the 52/138 jetting. To run acceptably, I have to turn the fuel screw out about 3 1/4 turns (otherwise real hard to start and it sits there and hiccups at idle). Obviously it needs a bigger pilot jet. However, I am using a stock filter, I have the snorkel in place, and the exhaust is completely stock. So, with no modifications, what size pilot should I try? I am not trying to get any more power, etc. I just want to improve the starting and idle.

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I would try one size larger pilot jet first. More is not always better. Before you change make sure the idle RPMs are at spec.Set the mixture screw with the the larger jet to the same turns as stock. Start and ride the bike until it is fully warmed up, at least 10 minutes. Then turn the mix screw in slowly until the motor starts to sound rough then turn the screw out until again the motor seems rough and do that slowly plus count the turns. Set the mix screw to the mid point of those turns. To test, on the next day do a cold start using the choke and no throttle. Does the motor start after only a few kicks? Yes, next ride the bike again long enough to reach operating temp. Shut off the motor wait about 5 min. and start again when hot. The motor should start after 1~2 kicks. Too lean the motor will take longer to not need the choke, too rich the motor will be hard to start when hot.

Edited by ohio rusty spokes

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Before you go changing pilot jets, remove the fuel screw and clean that passage well. A dirty passage or partial blockage will cause your problems. Same with the pilot jet itself, clean it too. The 52 may be right right size but if there's any blockage, the system isn't going to provide the amount of fuel it should. Same would be true if you dropped in a 55 with the fuel screw passage still needing cleaned.

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That is some really helpful info, I appreciate it. I will definitely try it just as you described. And by the way, I did clean the carb thouroghly and everything is in perfect shape. I will post the outcome in a couple of days as soon as I can pick up a jet.

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I have a 2003 XR400. It is a California bike, all stock with the 52/138 jetting. To run acceptably, I have to turn the fuel screw out about 3 1/4 turns (otherwise real hard to start and it sits there and hiccups at idle). Obviously it needs a bigger pilot jet. However, I am using a stock filter, I have the snorkel in place, and the exhaust is completely stock. So, with no modifications, what size pilot should I try? I am not trying to get any more power, etc. I just want to improve the starting and idle.

I put a 58 in my buddy's '03 Cal XR4 with no mods. Before that it was painful to start. He's happy now but I haven't had a chance to adjust the fuel screw yet. I also went up two sizes on the main. Mileage dropped from 220 to 180 miles for a 3.8 gal. desert tank.

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I was also wondering if anyone has purchased an extended or remote fuel screw for the XR400. I can get a small screwdriver in there past the California oil vapor canister but haven't tried with the motor running.

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I was also wondering if anyone has purchased an extended or remote fuel screw for the XR400. I can get a small screwdriver in there past the California oil vapor canister but haven't tried with the motor running.

I tried and failed finding a remote /extended fuel screw. Going to add and extension to the original.

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Okay, so I put in a 55 pilot jet from the stock 52. When I adjust the fuel screw, I start at 1 1/2 turns out. I can screw it in leaner and the revs drop at about 1/2 turn in from there. When I go back to 1 1/2 and screw it out richer, the revs don't drop even when out to 3 1/2 turns. Any more and the screw would probably fall out. Does this tell me that a 58 pilot may be even better since the midpoint range that the screw likes is somewhere between at least a turn out and at least 3 1/2 turns out? By the way, the bike runs great and starts better than with the 52.

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