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divebobber

TPS connection to carb

4 posts in this topic

I've got one for you, Gray. I checked the resistance (between yellow and black) of my TPS at closed and opened throttle. It was the same, about 2400 ohms, no matter what throttle setting. It's supposed to be 0 - 2000 at closed throttle and 4000 - 6000 at fully open. I decided to take it off and see if I couldn't clean it out and get it to work. When I took it off, I checked the resistance when the TPS shaft was manually rotated and it checked out perfectly. In the manual (pg 6-9) it looks like there's supposed to be some sort of junction piece between the carb shaft and the TPS shaft that connects them together. As it is, the projection on the carb shaft doesn't reach to the TPS shaft, and it's a female/female connection, so it appears that the little piece is a double male. Ever heard of this? So, my TPS was working but it was telling the CDI that my throttle setting was at idle. Wouldn't that significantly rob full throttle power? Until I find that piece, would you suggest just leaving the TPS unhooked? I forgot to mention, this is on a 2000 YZ426F.

Thanks ahead of time.

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Well, it will work a lot better with it unhooked than with it reading "idle" all the time. When it's unplugged, the CDI assumes full throttle, and times according to rpm.

Go to the Yamaha parts page:

http://www.yamaha-motor.com/sport/parts/home.aspx

Punch in motorcycles, 2000, and find "Motocross 4-stroke-YZ426" in the model list. On the carb page, look at item #43 ("collar"). This may be what you're looking for.

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It's really hard to tell by the pic, but I can't see what else that "collar" might be so I'm ordering it. I've never had it apart before, so it must have been removed by the previous owner. I've never been satisfied with the top end of this bike, now I may know why. I read many posts on the effect of unplugging the TPS. I guess my only concern is having advanced timing at lower rpm and throttle settings (lugging) possibly causing preignition. Thank you for the advice!

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I read many posts on the effect of unplugging the TPS. I guess my only concern is having advanced timing at lower rpm and throttle settings (lugging) possibly causing preignition. Thank you for the advice!

Actually, the timing won't be advanced any more than usual. The CDI advances the timing at cruising speeds in response to the low throttle signal, not the other way around. As the throttle opens and the load increases, timing is retarded to avoid detonation (not pre-ignition) and pinging. With the TPS unplugged, timing is still adjusted for varying engine speeds with the assumption that the throttle is wide open. There is no additional risk of pinging as a result, but part throttle "crispness" and fuel economy may suffer.

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