Fixed 01 WR426 with 03 450 carb; question

I've been screwing around trying to get my 426 to run smoothly on the road (supermoto) for four years. Finally just broke down and bought a 03 WR450 carb on ebay put it on and bingo. The problem was at 1/4 to 1/2 throttle cruising on a flat road doing 45 or faster and having a surge/hesitation that was really anoying, especially going through turns on the street. The old carb had excellent acceleration and top end. When dirt riding I never noticed the problem. I ripped the two carbs appart to compare and the only major difference I noticed was that the starter jet on the old carb is 65 and 78 on the new. This is a Canadian carb. I think it's 72 on US models. Does any one know what the starter jet is doing?

Does any one know what the starter jet is doing?
The starter jet meters fuel to the "choke" circuit when the choke is pulled out.

The starter jet is only for the choke circuit.

I guess that the starter jet is not the culprit. It's obvious to me that the two carbs are quite different. Can anyone post all of the specifications shown in the owner's manual for the 03 WR450 carburetor please?

OK. In case anyone reads this thread I've done my research and know all about the stock 03 WR.

OK. In case anyone reads this thread I've done my research and know all about the stock 03 WR.

Mind sharing? Inquiring minds would like to know. Thanks.

There is a link somewhere on Thumpertalk to download Yamaha owner manuals from Yamaha Australia. The manual I downloaded shows the following:

USA CAN

MAIN 150 160

AIR JET 2.0 2.0

NEEDLE OBDUT OBDUQ

CLIP POS 4 4

PILOT 45 48

PILOT AIR JET 70 80

PILOT SCREW 1-3/4 1-1/2

STARTER JET 65 65

The carb I purchased and installed has a 165 main, NCVQ needle set at 3rd clip, 42 idle jet, and 78 starter jet. I don't know much about the needle. Just starting to learn a little about needle options. I noticed that the bottom end is little weak but I'm running the WB E2 pipe with the plug in it. Once it gets up in the revs it really takes off. I haven't had a chance to dick around with main jet size and clip positions. That's next.

There is a link somewhere on Thumpertalk to download Yamaha owner manuals from Yamaha Australia. The manual I downloaded shows the following:

USA CAN

MAIN 150 160

AIR JET 2.0 2.0

NEEDLE OBDUT OBDUQ

CLIP POS 4 4

PILOT 45 48

PILOT AIR JET 70 80

PILOT SCREW 1-3/4 1-1/2

STARTER JET 65 65

Hey, can someone verify this?

 I'm about to order a bunch of parts, ( 3 different Yamahas, and one extra carb...) and I'd really like to know what jets are used in the Canuck version of the carb on my '02 WR426. I'm thinking of ordering stock stuff, and one set a shade richer for cold weather riding/tuning.

The Canadian carb also does not have a ACV system, hence the different sizes of pilot, pilot air jet, and pilot jet.

 

Also, the main and needle are based around stock airbox and exhaust, which you hopefully will not be using. 

You should be using an N needle (NCVS for example) and a 160/165 main when uncorked.

Both of those listed needles are way to lean for an uncorked motor.

 

 

Colder climates can use as large as an 85 starter jet too.

Good info, thanks! I didn't know about the ACV. I'll do some reading about that.

I understand from searching here, that the euro/Canadian exhaust isn't as restrictive as it appears. I REALLY like the idea of quiet, and easy starting and reliability are 10x more important to me than any increase in performance. I think I'll order both diaphragms, the slide seal thing, a new petcock, a one-up needle, and std and one up pilot, main and starter jets, and start in. Right now, it's below freezing in my garage, no hope of starting it. Happily, I did find the Canadian parts "fiche" on line, so I can order online from the USA using part numbers.

Edited by manotickmike

OK, I've searched.

What's ACV stand for??

Automatic Coast Valve

 

It enrichens the pilot circuit with the throttle is shut, during deceleration.

I leave mine in, and ignore it. 

Thanks!

 Say, is there a thread which details the differences between the US and Canadian bikes? I hear a LOT of rumours, I'l like to know for certain!

It's all in the service manual

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