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Lowedog

Main air jet on WR 450?

17 posts in this topic

My manual shows the MAJ as a 2.0. Everything I have read in other posts show a number similar to a main jet but more like 200 or so. These posts refer to 400's and 426's. Does the 450 carb have a fixed MAJ or something?

Lowedog

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I did'nt see a MAJ either :) but does anyone know what size the PAJ is. Could not find size of that listed in the manual. Is the adjustable PAJ something you can adjust from outside the carb.

Smoke :D

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...does anyone know what size the PAJ is. Could not find size of that listed in the manual. Is the adjustable PAJ something you can adjust from outside the carb.

I don't own a 450, but I'm 99% sure the PAJ is a 100.

This jet is behind the carb bell, so you can adjust a PAS from the outside only if you take off the air boot, and only if the bell on the 450's carb has a slot to access the air jets, but most of the FCRs I've seen have this slot.

Hope this helps.

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Isn't the main air jet called the throttle slide? :)

Nah, the MAJ is a jet, just like a fuel jet, but it meters the air that the carb delivers to the main fuel jet. It is located behind/underneath the carb bell.

The slide is the actual throttle, and the cutaway can be changed on many carbs to affect low rpm jetting. But in the FCR, unlike many two-stroke carbs, the slide is not something that is changed to affect mixture. That I know of...

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On page 2-8 of the manual it shows the specifications of the carb. It shows the PAJ as a # 70 for the US model and a #80 for the euro model. I'm running a 42 pilot so I think I'm close on the PAJ. I have a PAS from Sudco ordered. I hope it works on the new carbs.

The spec for the MAJ is shown with the symbol for diameter then 2.0 (I can't find a key for that symbol but is a 0 with a line through it). Could that be 2MM?

Also it list the leak jet as a #70 for the US model and a #50 for the euro. Any one know what the purpose of this jet is? I have seen another post about a rework of the leak jet to make it smaller.

Lowedog

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The spec for the MAJ is shown with the symbol for diameter then 2.0 (I can't find a key for that symbol but is a 0 with a line through it). Could that be 2MM?

No, 2 mm would be colossally huge for any MAJ. My gut tells me it is a 200 (signifying .2 mm), but I've no real idea, I don't own a blue 450.

The leak jet meters fuel delivered by the accelerator pump.

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there are some short memories about :D because we once had a thread all about making the MAJ larger and everyone was taking 2.3mm drill bits and making their MAJ's into #230's.

now put two and two together and what have you got when you get a 2mm MAJ?

:D:)

Taffy

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Thanks Taffy! :)

Do you have a chart for MJ to MAJ relationships?

I have found your PJ to PAJ and have copied it for referance.

Lowedog

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Well the PAS doesn't work on the new carbs. The PAJ is totally differant. Wish I would have investigated further before ordering it. :) I assumed they would be the same. Anyone need a PAS? I will make you a good deal on it.

Also on the MAJ, it doesn't have a removable jet. Just a hole in the the carb right next to the PAJ. I assume this hole tapers down to 2mm. Thus the dia.2.0 secification for MAJ in the manual.

If any one has the part numbers for PAJ's for the new carb please let me know. I would like to try a larger one with the pilot I am running.

Lowedog

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Well the PAS doesn't work on the new carbs.

Wow. That is surprising. Why not? How is it different?

I don't get that. I'm pretty sure there is a Yamaha PN for the YZ PAJ, size 100, off the 450 fiche :

5TA-14943-27-00

But there is no optional sizes (unlike needle, main, pilot etc.). So, if it is different, but there are no optional sizes, and a "normal" FCR PAJ doesn't work, then why bother to make it a removable jet?

Maybe I should just go back over to the red side until I own a blue 450. I'm confused. :)

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I beleive the threads are different on the WR450 FCR PAJ jet and the Adjustable Sudco PAJ may not work on the new WR450s. I have a 100 and 70 PAJ they have a 4.5mm diameter thread. I am talking to Sudco to see what options we 450 owners have. So far we just need to buy several jets to get the adjustability. Who has installed the Adjustable PAJ on a WR450? Does it actually thread in?

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Yea, the threads for the PAS from sudco are 6.8MM

Another strange thing is the YZ 450 fiche shows no leak jet. My manual shows a #70 leak jet for the WR. If I'm trying to mimic the YZ jetting, what's up with the leak jet? The fiche for the YZ 250 F shows a #100 leak jet standard with optional jets from #70 to #130. How does the 450 not have a leak jet?

Have you tried the #100 PAJ Indy? If so, did you notice any differance?

Lowedog

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lowedog- I'm also trying to change my carb over to yz jetting. The leak jet has me very confused too. I started a thread over on the yz side to try to sort this out. The yz also has a different part number for the acc. pump diaphragm and the fuel screw.

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Hey Lowedog,

Unlike Taffy, I need a rich Pilot circuit for the Thunder Alley Pipe. It flows extremely well off idle and at lower rpms. I am currently running the 48 pilot with a 100PAJ and it is richer that with the 70 PAJ. I like the combination, I was very lean between 1/8th and 1/4 throttle. Needle diameter helped but could not cure the problem the pilot needed to richen up to make this beast run. I tried going the other way but the backfiring was too bad and loss of pull was noticeable. I have no idea how some of these bikes are running lean pilot circuits. I hope the M or N diameter needle does the trick for me. I have gone down and tried 45,42,40 PJ's with the 70 PAJ and the backfires and 1/8th to 1/4 throttle just got worse and pulled like a weenie . I am going to try a 50 PJ next and see where being too rich takes me. I am seeing results that do not agree with Taffy. I seem to be proving James Dean's and Kaze's experience to be more effective for my set up. I want to make it clear that I am still trying to get the jetting to where I had it with the stock pipe. I had that set up dialed in. My Thunder Alley Pipe just snap crackle popped 1/8th to 1/2 throttle when I first installed it with my dialed in jetting I am trying the EMM,EMN neddles next to see if that will let me bring the pilot circuit back down but I suspect it will let me stay at 48/100. I have rejetted 10 times these last few days tring to dial in my pipe.

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