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WEAL

05 450 hanging idle gone!!!

6 posts in this topic

After playing around with different jets and airjets for a while which all helped a bit but did not cure the hanging idle completely I checked the TPS. All measurements were as specified in the book so I thought I will try it unplugged. Wow - now the idle could be set anywhere between 1000 and 2000 revs - the bike responds better than ever and best of it all it comes down to the set idle the moment I shut the twistgrip! After all that jetting I was quite sure that it had something to do with the ignition been lazy to retard. I went back to the std jetting for this bike and everything works as it should. Tried the bike on the local track and its better than ever. Why does my TPS slow the ignition? Is my CDI not able to incorporate the info from the TPS fast enough to retard the firing point at the right time?

I realy wonder about this as the bike is so much smoother and better without the TPS connected.

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Weal..I have a 04 450f and was wondering the same thing after reading alot of posts about the TPS. My best guess is that the mapping for the the TPS is pretty vague. The TPS tries to anticipate the amount of fuel needed at certain throttle settings based on the anticipated increase in air. I think the slower feeling throttle response with the TPS hooked up is the amount of time it takes for the TPS to "figure out" what it is reading, communicate with the black box and make the appropriate changes. In reality this takes milliseconds but may cause the "slow" feeling. I could be totally wrong here and I hope the other guys will post some thoughts on this as I am kind of wondering about this myself.

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At least on my bike it took up to 3 seconds for the idle speed to come down!! I have seen the same happening on a 07 / 250 Yam and a 06/450 Yam as well. As soon as the guys set the idlespeed higher than around 1000 revs/min the trouble started. As they are too lazy to find out they leave it at a very slow idle - as I don´t like the slow idle and the incorporated hammering the piston skirt gets with low revs I tried for much too long time to correct the problem - now that its gone I don´t care anymore for the TPS as the bike works as it should. This is my first Yam and I was pretty disappointed as I never had any issues with the 04 450 Honda I had before.....

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Weal..I have a 04 450f and was wondering the same thing after reading alot of posts about the TPS. My best guess is that the mapping for the the TPS is pretty vague. The TPS tries to anticipate the amount of fuel needed at certain throttle settings based on the anticipated increase in air. I think the slower feeling throttle response with the TPS hooked up is the amount of time it takes for the TPS to "figure out" what it is reading, communicate with the black box and make the appropriate changes. In reality this takes milliseconds but may cause the "slow" feeling. I could be totally wrong here and I hope the other guys will post some thoughts on this as I am kind of wondering about this myself.
The function of the TPS is to provide load information to the CDI for the purpose of increasing the ignition advance at part throttle. It does exactly what the vacuum advance unit on older car engines did. Since at part throttle the charge of fuel and air in the combustion chamber is less dense, dynamic compression is reduced, and in order to get the cleanest, sharpest part throttle repsonse possible, the ignition advance is increased under lighter loads to offset the lower dynamic compression and get the most out of the fuel charge.

When the TPS is disconnected or fails, the CDI sees that as meaning that the throttle is always wide open, and sets the timing based only on changes in engine RPM. At any engine speed, the WOT timing would be the most retarded.

Three possibilities occur to me as the root of the problem the OP had that was cured by a TPS disconnect:

1) The TPS was in fact either faulty, or set wrong, despite what he was told, and the closed throttle signal voltage was too high, leading to too much ignition advance.

2) The CDI is faulty in that it does not respond correctly to TPS inputs.

3) The TPS and CDI are both fine, and there is an underlying issue with the idle circuit in the carb that is being covered up by the artificially retarded ignition timing.

I'm also curious as to whether the blue wire from the neutral switch is connected or disconnected on this?

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Grayracer - the blue wire is still connected to the neutral switch - should I disconnect this and try the TPS again? The jetting is 48 pilot, fuelscrew 2 turns out. All measurements on the TPS were well within the limits as dictated by the yam book.

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I wouldn't disconnect it, but it might be interesting to check it for function. The wire should be open in any gear, and short to ground in neutral.

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