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forklord

Engine bogging/sputtering/coughing? FIX IT!

14 posts in this topic

Remove TPS (throttle position sensor). I've been posting here recently with tons of questions, rejetting, exhaust , ect. only to find (thanks to EDDIE!) that it was a matter of simply disconnecting my TPS from the head of the carb to the computer. it runs along your frame as you can see in the pic. bike runs ****ing amazing now! enjoy

tpsd.jpg

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I've read about this contraversary before. Some say they notice a difference, others say they didn't notice jack shiz.... My only issue with what you are doing is once you disconnect the TPS, you either have full retarded or full advanced ignition timing 100% of the time. (I am not educated enough on the YZF TPS to post which timing curve, but it's got to be either or). The only thing I can make of this is maybe there is some TPS's out there that have a "glitch" in the ohm output at a certain throttle opening, and the ignition is simply reacting to incorrect ohm inputs ?

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for the headache its caused me and the damn sputters im willing to take a chance. it completely eliminated it. like...completely. eddie says it wont hurt anything on a yz but who knows. i dont know enough about ignition on bikes to even know what it was...how do you think this could adversely affect the bike Polar_Bus? i see you were one of the guys tryin to help me out on my other posts. thanks!

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I did the same thing on my 06. The bike felt like it had a clogged carb or something. After disconnecting the TPS it runs super smooth.

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My tps went out on my 1999 yz400f about 7 years ago and has been unplugged since then without any problems.

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Some have reported after disconnecting that the bike now seems a bit flat/low on power

Also if you did remove, do you have to adjust your jetting?

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I want to know more. I realy don't want to post any info on this subject yet, but I do find this subject interesting. :banana:

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More info:

http://www.thumpertalk.com/forum/showthread.php?p=3680449

Essentially, if the TPS is working right, and adjusted correctly, disconnecting it won't accomplish much. But, if it's malfunctioning in any way, it can make a lot of difference to disconnect it.

So if you unhook it just to see what it does and you don't notice a difference can you just hook it back up or does the TPS have to be reset somehow?

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I be the first to say "I still don't get it gray". I understand that cars have had it for years and the TPS was realy for EFI systems, but why did we get it on our flat slide carbs? I got two strokes with it on the carbs and I can not see one reason its on a two stroker. I'm no pro on the four strokes, but if the TPS can just be unpluged with no problems to the motor, over heating, jetting or will it weaken the life of the CDI, then why was the carbs designed with a TPS? I know your hyperlink said it advanced the timing, but if you can unplug it, does the timing change that much? I did a little research last night and realy didn't find anything that thrilled me. I know I can't be the only one wanting more from this subject.

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I think what you should get from this is:

First off, variable timing was NOT designed strictly for FI, it just happened that it became readily available around the same time, it was designed to improve your engine's efficiency at both fuel consumption and power output throughout the RPM range it uses.

The reason Yamaha put a TPS on the bike is to give it VARIABLE timing, this allows them to get better power throughout the full RPM range, essentially, that is what variable timing does - it allows you to get the most power all the time through the rpm range. Before variable timing, engines were plagued with flat spots at certain rpms because of the ever changing environment - set timing will only work well in the rpm range it was set up for but not outside of this relatively small window.

If you unplug the TPS you will run with a single preset timing (advanced in this case) and you will likely notice a slight power loss in certain RPM ranges because you've gone back to the days pre TPS/variable timing - nothing wrong with it, just not as efficient at giving you power everywhere in your RPM range.

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If you unplug the TPS you will run with a single preset timing (advanced in this case) and you will likely notice a slight power loss in certain RPM ranges

That's not accurate. You need to go back and review the link I posted. The CDI maps timing based on two input variables, RPM and throttle position. When the TPS disconnects or runs out of range, the CDI ignores it, and assumes full throttle for that half of the equation. It will continue to map timing according to engine speed, as it will still have the tach signal from the trigger coil as long as it runs at all. So, no, the timing will not be fixed at a single setting. There will be no discernible difference in performance at full throttle with or without the TPS connected, because there is no difference in the input to the CDI. With no TPS, the CDI sets the load input parameter at full throttle anyway.

The second inaccuracy is that a high TPS voltage, indicating low throttle openings, causes the timing to advance. That means that disconnecting the TPS will retard, not advance, the timing at part throttle.

Variable timing is nothing new, and neither is timing varied according to load. That's been done in the automotive world since the the 1930's or earlier. Timing adjustment for engine speed was managed by centrifugal weight mechanisms, and timing variation for load was done by means of a mechanism operated by manifold vacuum. Intake vacuum rises and falls according to throttle position and engine speed, so it was perfect for that purpose. The advent of electronic timing controls began around 30 years ago as emission control regulations grew ever more demanding. These lent themselves much more readily to motorcycles and were adopted starting around 15-20 years ago.

The reason that timing advance needs to be controlled based on load is that it improves driveability, fuel economy, and general part throttle crispness and performance. This kind of thing is much more noticeable and significant in a car or a road bike (although there are a number of conditions under which a dirt rider would notice it, too), so disconnecting it doesn't usually cause too much excitement one way or other unless it cures a problem caused by a defective TPS.

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