TPS & Floats Question

[davidwagner]

Hi everyone! I bought a 2004 GS500F as my first bike a few months ago. Runs okay, but been working for a couple months on figuring out what's causing the somewhat poor idle, somewhat sluggish throttle response, and revs that don't fall as fast as expected. I've cleaned the carb and had it apart multiple times. Just been going through it a last time before I move on to engine stuff like checking compression and valve clearances. I just tested the TSP sensor, and it checks out according to my Haynes manual. Reads 4.86 kohm, which is right in the middle of the 3.5 to 6.5 kohm range that's acceptable. The manual also mentioned that with the throttle wide open, the middle and outside pin should read 76% of the resistance of the two outside pins (4.86 kohm on mine). This would be 3.69 kohm, but mine is reading 3.96 kohm with the throttle wide open. You guys know if 250 ohms is enough to make a difference? This definitely seems like splitting hairs, but I've been tinkering with this carburetor enough that I'll try anything haha! Figured I'd ask you guys before pulling the thing off, because getting it right at 3.7 kohms without alligator clips will likely be a big PITA.

Also, I've noticed that the floats in my carb aren't level. When one is at the OEM 13 mm height, the other is sagging a couple mm lower. Since they're a single plastic piece, not sure if there's a way to bend them or if I need to buy two new floats? Or does it not even matter? Anyone else noticed one side of the float sitting lower than the other?

p.s. Y'all have an awesome forum here! Unreal amounts of good info. Appreciate the service you do for fellow riders 

[The Buddha]

OMG, that TPS doesn't do nothing. Dont confuse yourself. You dont got fuel injection.
Cool.
Buddha.

[mr72]

plain and simple, switch to 20 pilot jets, while the carbs are open replace all of the o-rings including the hard to get to ones on the pilot adjustment needles, an then set pilot mixture correctly and idle speed with the bike fully warmed up and the problems will most likely go away.

[davidwagner]

Thanks guys! I figured the TPS wasn't too important. Did a bunch more reading last night (including your blogspot carb issues article, Josh, which was excellent!), and I've got the new o-rings and the size 20 pilot jets in the mail! It has been pretty cold in Cleveland, so definitely possible I didn't have the bike actually warmed up all the way. Got the carb looking extremely clean inside and out, and I'll retest once those parts get here and let you know if it's fixed or not.

[chris900f]

I'm going to jump in here, because I've been trying to figure out if the TPS actually improves performance
or is just another emission control. I've heard the bikes still run ok if you unplug the TPS. So...

Since the parts diagram only lists one rotor, the ECU must control idle advance, which is different in
different markets, and a very low 5 degrees here in NA but 12 in the UK. I believe this was done to
meet emissions without the pair-valve thing. (12 degree UK bikes do have the pair valve)

The ignition rotor looks something like a missing-tooth wheel that you would see in an EFI set-up,
except that the teeth are irregular sizes. Since the ECU is not digital (sort of guessing here, re: schematic)
and uses a vibrating crystal to "calculate" optimal timing; it seems that max timing is pre-set by the rotor, and
TPS likely just retards from a pre-set curve.

Is this correct? If so wouldn't it be better to unplug it and default to the pre-set ECU curve, so at least once off-idle,
you would be getting the max timing at each point in the RPM curve instead allowing the TPS signal to pull down the
timing?

[mr72]

Remember it takes like 20 minutes of actual riding for it to get completely warmed up. A lot of us don't ride that far most of the time. Bike should run ok once set up right even when it's cold but you have to warm it up ll the way to get it set up right.

[The Buddha]

I'm going to jump in here, because I've been trying to figure out if the TPS actually improves performance
or is just another emission control. I've heard the bikes still run ok if you unplug the TPS. So...

Since the parts diagram only lists one rotor, the ECU must control idle advance, which is different in
different markets, and a very low 5 degrees here in NA but 12 in the UK. I believe this was done to
meet emissions without the pair-valve thing. (12 degree UK bikes do have the pair valve)

The ignition rotor looks something like a missing-tooth wheel that you would see in an EFI set-up,
except that the teeth are irregular sizes. Since the ECU is not digital (sort of guessing here, re: schematic)
and uses a vibrating crystal to "calculate" optimal timing; it seems that max timing is pre-set by the rotor, and
TPS likely just retards from a pre-set curve.

Is this correct? If so wouldn't it be better to unplug it and default to the pre-set ECU curve, so at least once off-idle,
you would be getting the max timing at each point in the RPM curve instead allowing the TPS signal to pull down the
timing?

The advance is dwell based on the largest nose on the advancer. The advance is set by an IC. I am talking about yamaha that I have opened up. I dont believe there is a retard type, but not 100% sure cos never opened a GS one.
The 04+ advancer and single pickup, and electronic tach - no idea how it all works. Never owned anything after 00. Even the 00 that's in my facebook profile pic is a 95 with 04 body on it.
Cool.
Buddha.

[chris900f]

The advance is dwell based on the largest nose on the advancer. The advance is set by an IC. I am talking about yamaha that I have opened up. I dont believe there is a retard type, but not 100% sure cos never opened a GS one.
The 04+ advancer and single pickup, and electronic tach - no idea how it all works. Never owned anything after 00. Even the 00 that's in my facebook profile pic is a 95 with 04 body on it.
Cool.
Buddha.

Yes, that ECU on the 04+ bikes has a lot of functions, internal relays, the igniters and even a 5v power supply for the TPS and the Tach output. In simple 2d system like the Dyna2000, the pick-up plate position determines your maximum advance; and the circuitry operates as a delay(like a guitar pedal lol) after the 1st revolution, subtracting from the maximum based on RPM. On those Dyna systems there are only 35degrees of "delay" from max. So if you set your plate for 40 degrees, you are also adding 5 degrees at idle.

By adding the TPS variable to the mix (3d) you could alter the amount of delay based on whether your accelerating or just sitting at a steady cruise. I think Suzuki's goal here was just to reduce advance at cruise to burn less fuel (and make less power) as an emission control measure. The fact that the bike runs fine without TPS, means there must be a "master" curve representing the maximum advance at each RPM point. For example the manual tells us 40degrees@4000rpm, but if you're at 4000rpm @ 1/6 throttle the system can "see" that you're not loading the engine very much, and can reduce the amount of advance to save gas. As far as the wonky looking rotor, I think you're correct. The big tooth represents the range of advance available--as for those other teeth I'm guessing they are there to keep the "vibrating crystal" energized, like a quartz timing movement in a watch (from the 1970's lol).

[The Buddha]

You're thinking more CDI vs TCI. The CDI has a capacitor that charges through the cycle the inductive pickup isn't in the spark stage. On a TCI, its got battery's 12v and the transistor just connects the 2 sending a 12v signal to the 30K volt capable step up coil.
As in its not "charging" when its not sparking, its just got the 12v battery voltage sitting there, the instant it gets the induct signal it connects the 12v and instantly it breaks it as the induct signal is gone.
Cool.
Buddha.

[davidwagner]

Just an update on my progress: I think I've gotten the carb sorted out, but can't know for sure since the engine still doesn't make proper power and won't really go over 60 mph. Just falls flat on the highway. Measured the valve clearances, and all are within spec. Here are the values below:

Left hand intake valve: .002"
Right hand intake valve: .0025"
Left hand exhaust valve:. 002"
Right hand exhaust valve: .00225"

I did a compression check and got the following results, which I believe is my problem.

Left cylinder dry warm compression: instantly jumped to 97 psi
Left cylinder wet warm compression: instantly jumped to 104 psi, but on second and subsequent tests, it only got to 92 psi or so, which leads me to think that the increase was likely due to lost volume rather than sealing any leak in the piston rings.
Right cylinder dry warm compression: instantly jumped to 90 psi
Right cylinder wet warm compression: instantly jumped to 105 psi. Subsequent cranks lowered to about 100 psi.

Since my Haynes manual says 142 psi is the minimum acceptable for both cylinders, it seems I have pretty damn low compression. Leaking rings doesn't seem likely, because pouring oil into the cylinder for a "wet" compression test didn't really raise the values that much. Let me know if you think the 10ish psi jump is indicative of leaking rings or not, though... I'm thinking it has to be a leaking head gasket, although I'm not seeing any fouling in that area of the head. I think I'll just replace all the seals and gaskets and reassemble and retest to see if it solves the issue. Let me know your thoughts, though

[davidwagner]

Sorry about the late final update. Had it solved for a while, but every time I remembered to post, I haven't had access to a computer that could access the site.

Final update on this:

Problem I was having: bike sounded like crap, and made little power, bogged in the mids and couldn't go over 55-60 on the highway.

Solution: I failed to plug in the left coil pack after testing the ignition system a while back. The low compression seems to not be an issue, and there was nothing wrong with the carburetor at all. The bike will hit high 80s on the highway, no bogging in the mids, sounds great, generally runs like I would think it should. As soon as I plugged the other coil pack in, it ran like a champ!

Thanks for the help everyone. Keep up the good stuff on this forum. Great resource for these bikes!

[mr72]

I assume you have tested it running after it is fully warmed up, like 20+ minutes of actual riding on the road?

My bent valves causing low compression only manifested an issue when it was fully warmed, at which point it would not run at low rpms and would die if you tried to let it idle. Min rpm was like 7K. Made it quite useless. But I had on cylinder <80 psi IIRC, the other like 105 like yours. Bent valves on both.

Valve clearance check doesn't tell you everything. If it's not leaking past the rings then it has to be either a blown head gasket or it's leaking past the valve seats. If you have bent valves or carbon buildup causing the valves to not close completely then you will get extra big valve lash measurements, low compression, and any day now probably further bent valves or a burnt valve.

I would be very concerned about those compression numbers, and make a plan to correct it.