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99 YZ400 jetting w/James Dean Kit

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Hello,

My problem is engine is cutting out between 1/8 to 1/4 steady throttle (roundabouts) and pops bad when you let off the throttle. It has also been hard to start, would fire...sputter...die, repeat about 8 times until it finally idled. I'm also in Raleigh, NC so most riding is 0-2500' The settings were:

James Dean kit

170 main

Blue needle 4th clip

65 pilot something (not sure which is which but this looks like a normal jet)

52 pilot something (the one next to it that has little holes in the end)

1 1/4 turns on the air/fuel mixture.

I've turned the screw out to 2.5 turns and it has started easier but it still cut out on 1/8-1/4 throttle. Also seemed to get rid of the off idle bog. I then raised the needle 1 clip but it still does it, may be a skosh better.

From reading past threads on this I'm curious about the pilot jet(s). It appears someone has changed some things (I bought this used obviously) from what James Dean has stated in other posts. My original main jet was a 180 also. Now to complicate this (maybe), the engine was rebuilt right before I bought it and from what others have said concerning how hard it pulls that the mechanic -may- have put a 426 jug on it. is that easily possible? The original owner let it run out of coolant and the whole motor had to be rebuilt (came from Alabama as well). Anyway, I guess I'm wanting to know if I need a different size pilot set up. I'm raising the needle 1 more clip to see if it helps but from reading other posts I doubt it will...

Thanks,

James

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I should also add I have a Ready Filter with an open airbox (no lid) and a non-stock header with the stock muffler that has a Pro Moto spark arrestor endcap.

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The stock pilot jet on the '99 was a #45 (not 52). Try using the stock pilot jet and blue needle, clip position #4, #170 MJ.

There is a chance that the big pilot jet was installed because the carb slide was installed incorrectly. The bike will run horrible at low speeds, pop and backfire, and overheat (is this a coincidence?).

See- 25566126

and - 25566229

Pull the carb out from the rubber boot at the motor and make sure the slide plate has the square end down, and not the "V" end down.

Thanks,

James

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Checked just now and the carb slide is correct. I'll try the #45 pilot jet when I get my hands on one. I'll go research this but does the smaller jet reduce air flow thereby richening the mixture?

Thanks for your time on this.

James

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JamesF,

The #45 will be leaner, as it meters fuel. Use the fuel screw to adjust the idle mixture, starting at 1 1/2 turns out. If the bike needs more fuel than a #45 or #48 flows, I would look for air leaks. It would be unusual to need a #52 with the blue marked needle in the middle clip position.

Thanks,

James

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Good deal, thanks for the explanation. I have to order the jet (s) as none are local that I can find. Hopefully by next weekend I'll know something.

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The other thing I forgot to mention was I practically never have to use the hot start button. Even stalling it in the woods on a 90 degree day. Don't know if that has any bearing on anything as I haven't read exactly what pulling the hot start alters in the carb.

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Ok. Got the 45 jet last Wed. Didn't have time to test ride it until Sat though. Took it for a 60 mile ride in 50 degree weather at a few thousand feet (NW of Franklin, NC in the mountains) and the carburation worked much better. I did have to turn the air/fuel screw out 2 1/2 turns to get rid of the off idle bog when you snap the throttle and to get it to start and idle the 1st or 2nd try instead of the 5th or 6th time. It was in the low 40's when I had to do these settings. So I'm pretty happy with it now. I do have a 48 jet I could try at some point. I also bought a clamp for the air box to carb attachement... prior there was none and I would always zip tie it on. Don't know if that would have any bearing on my problem or not.

Thanks for your help.

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