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Ronnie Mac

Leak jet?

22 posts in this topic

Went to my local yamaha shop today to pickup new spark plug. While I was their, I asked if they had any leak jets (#40). They looked at me like I was nuts and called the head mech who said he has never heard of it! Is this a slang name? Could anyone hook my up with some part numbers and how I to can have a #40 leak jet. :thumbsup:

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yes they do, they come stock with some thing like a 70 and i put the 40 in with a 155 main 48 pilot and it runs like a dream (no baffle fmf header with yzpipe) the leak jet monitors the amount of fuel delivered to the fuel pump assembly (accel. pump).... the lower the number the more gas, high.. less... :devil::thumbsup:

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Cant seem to find it on the online parts page. What number would it be on the exploded view? And cant seem to find it under the 4jt-1494f-03-00 number. I might be looking in the wrong area.

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Gonzo is correct concerning the 400's 426's and the 03-04 450's.....

Yamaha announced earlier this year that they were instituting the leak jet in the 05-450's.

The 250's have always used leak jets, that why you can find them on the fisch.

Bonzai :thumbsup:

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Go to the Yamaha website and look at the online part catalog.

I think that you want item #20 (#40 slow jet, pn 4MX-14948-03-00) on the carb page. Take a look and let me know.

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slow jet is what they call the pilot jet the #40 leak jet yam part # 4jt-1494f-03-00 it is not shown in the manual for some reason? :thumbsup:

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yamakaze, the '03, '04 WR450's use a leak jet. sorry but it's there, in the bottom of the float bowl where it belongs. '03 used a 90, '04 went to a 70.

R.M., it shows up as #14 on the carb blow-up in my manual ('03). the 4JT-1494F-03-00 is a yamaha part number.

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All OEM jet part numbers can be found at ThumperFAQ.com

Jet OEM Part Numbers

YZF/WRF Leak Jet 4JT-1494F-XX-00

#130 XX = 33

#120 XX = 31

#110 XX = 29

#100 XX = 27

#90 XX = 23

#80 XX = 19

#70 XX = 15

#60 XX = 11

#50 XX = 07

#40 XX = 03

#35 XX = 01

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IS THIS ONE OF THE THREE JETS IN THE BOTTOM? IT IS TO THE REARE OF THE MAIN JET AND IS ABOUT 1/4 LONG? THE ONLY WAY YOU CAN GET TO THIS IS BY TAKING THE BOTTOM OF THE BOWL OFF.

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Mtrablue what year and what kind of exhaust and jetting are you running? I've got the sx powerbomb with a stock YZ muffler. I've only changed the main so far to a 175 I think and experiencing a slight dead spot with quick twist of the throttle.

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TREEBARK,

I JUST GOT DONE JETTING AN 04 450 WITH THE SAME SET UP YOU HAVE. FOLLOW THE EUROPEAN SET UP IN YOUR MANUAL FOR THE MAIN AND THE PILOT. I BELIEVE IT IS A 172 MAIN, 40 SOMETHING PILOT, CLIP #5 ON THE NEEDLE (IF YOU HAVE A BOG GO TO CLIP #3),AND 2 1/2 TURNS ON THE FUEL SCREW.

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sanmann, the leak jet is in the float bowl itself. it bleeds (leaks?) fuel from the accelerator pump charge to allow fine tuning. '03/'04 wr's are a bit lean on the fuel squirt so a smaller leak jet puts more fuel into each squirt. i think the 426's had the too much squirt. that's where the bk mod came from. if i write squirt one more time, i'll blush.

tree bark, i use the stock exhaust (gytr stainless header) with gytr insert. i've been playing with my jetting but when i ran the show-me 200 duel sport in june i ran, 45 pilot, 155 main, JD red needle with the clip in the middle, 50 leak jet, pilot fuel screw out 1 3/4 turns. i ran the main a little lean (a 160 would probably be best)to try for just a little bit better millage. not a lot of main jet time on that ride.

i have since blocked off the acv and went to a 42 pilot. i think a 40 might work a bit better. i've run the fuel screw in to about one turn out and there is no off throttle popping. this weekend i'm going to try the 100 pilot air jet/ 40 leak jet combo. i will leave the 42 pilot in as the pilot air jet will put more air in the pilot cicuit. as you can tell, i'm always mess'n with stuff.

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Sorry Gonzo, I found the leak jet in my manual( it does pay to look at)in the 2003 manual its number 14. Orderd mine today.(sure wish I could spell) 5th grade was very mean to me :thumbsup:

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Mtrablue,What does acv stand for? It seems you've got an understanding of these carbs, Can you tell me what the function of all the jets and the role they play for each of the circuits? Where do you ride mostly?

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