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oz426

Bk mod on 02 model wr 426 ?

4 posts in this topic

Hi, I did the BK mod, and changed to YZ timing last night on my '02 WR426, and i've just got back from riding, and it's like a new bike. I think it'll take a few rides to get used to the extra punch right through the rev' range. I lot of people have said they lost some bottom end by going to YZ timing, but I didn't notice it. As to your question, my '02 model had about 3.5 seconds continuous spray from the accel ' pump, I reduced it to somewhere between 0.50, and 0.65 seconds spray (my youngest son was working the stop watch, so we checked the spray duration about 30 times until we got a consistent reading between those two figures). I used those figures as an initial baseline, but the bike feels great as it is, so I don't think i'll mess with it any further. The reason I did the BK mod' to start with, was that when I was putting around through very tights tracks, on and off the throttle all the time, the bike would bog, and sometimes I could even smell petrol. Anyway the BK mod', and YZ timing combined are dynamite, I wish I had done them seperately, but it was too easy to do the timing when I already had the tank, seat and carby off. Motoman 393's site has excellent photo's and instructions for both the BK mod', and the YZ timing, good luck, Chris.

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Hey Chris, thanks for your reply. I am cuurently thinking about changing to yz timing myself, but was unsure if i wanted to risk losing bottom end power. Now that i know that 02 models require the bk mod i'll probly check my pumps spray length and do the bk mod this weekend and i may as well try yz timing while i'm at it.

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I forgot to mention, but if you decide to do the YZ timing, be VERY careful not to drop the bearing retainers out of the cam holders. As you're lifting the cam holder clear of the head, it may appear that the retainer is firmly attached, but in my case, when I lifted the exhaust cam holder, just a thin film of oil was holding it in place, and when it dropped I was lucky not to lose it inside the motor. I'm pretty sure the instructions on Motoman's site warn about this, but you still need to be very aware, as a simple 1 hour job could get real difficult real quick. If you do the BK mod' and the YZ timing, i'm sure you won't be disappointed.

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