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09 GS500 stumbles when accelerrating

Started by motoitalia, January 14, 2022, 02:27:53 PM

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motoitalia

Hi Guys, new to this group. My 09 GS500 idles fine but stumbles and falls flat when I give it throttle, I have to rev to 7000  to take off from a stop. Carbs are cleaned and adjusted, TPS is working correctly, I've tried with and without vac lines in place (plugged off)

cbrfxr67

Any mods on it?  Personally I'd play with washers and settings to see if I could tune it,.. Supposing everything else is in order,..
"Its something you take apart in 2-3 days and takes 10 years to go back together."
-buddha

mr72

Let's hear what work you've done on it recently. I'd guess one pilot jet is clogged.

motoitalia

#3
Hot tanked both carbs, new jets, (#20 pilots) set tps, replaced electric vacuum valve. No mods, stock air box and filter, stock pipe.
also replaced the carb mounting boots

Bluesmudge

What do you mean by "set tps"? AFAIK the throttle position sensor is a black box that you can either plug in (3d ignition map) or leave unplugged (2d ignition map, possibly better performance in 1st and 2nd gear) but beyond that you can't change any of the settings.

SK Racing

A TPS can be "calibrated" by rotating it to a certain position and tightening the screws. Exactly how to find the ideal position, is still a mystery to me.
You don't stop riding when you get old, you get old when you stop riding!
1939 Panther 600cc Single - Stolen, 1970 Suzuki 50cc - Sold
1969 Triumph Bonneville 650 T120R - Sold, 1981 Honda CB750F - Sold
1989 Suzuki GS500E - Sold, 2004 Suzuki GS500F - Current ride

mr72

On other motorcycles (like my Triumph and my dad's TU250X) there is a TPS adjustment procedure where you measure voltage or resistance of the TPS at closed throttle and WOT. I suspect the mystery is only how to adjust it correctly on a GS500?

On EFI bikes, this is an absolutely critical adjustment.

SK Racing

Yeah, exactly. I'm baffled that it's not covered in a service manual.

The video below shows how to do it on a Chinese engine, by measuring the voltage. If only we knew the critical voltages for the GS.

www.youtube.com/watch?v=LMtHxWypWkY
You don't stop riding when you get old, you get old when you stop riding!
1939 Panther 600cc Single - Stolen, 1970 Suzuki 50cc - Sold
1969 Triumph Bonneville 650 T120R - Sold, 1981 Honda CB750F - Sold
1989 Suzuki GS500E - Sold, 2004 Suzuki GS500F - Current ride

SK Racing

Maybe we should determine the correct voltage empirically by measuring a few well running bikes' TPS voltage at idle position, and taking the average.
You don't stop riding when you get old, you get old when you stop riding!
1939 Panther 600cc Single - Stolen, 1970 Suzuki 50cc - Sold
1969 Triumph Bonneville 650 T120R - Sold, 1981 Honda CB750F - Sold
1989 Suzuki GS500E - Sold, 2004 Suzuki GS500F - Current ride

sledge

#9
With the throttle closed check the resistance across the two outer terminals, it will be somewhere between 3.5K and 6.5Kohms.
With the throttle fully open the resistance across the middle and rear terminal needs to be 75-76% of the initial reading.

Example.........5k across the outer terminals means you need to see between 3.75 and 3.8K with the throttle wide open.

Sounds complicated but its not, use a very accurate or calibrated digital meter. The terminals are difficult to reach and slight movements of the TPS body make a big difference so go at it gently.


BTW......try balancing the carbs.

SK Racing

Interesting! Thanks for that, Sledge.  :cheers:

Btw, is it mentioned in a manual somewhere?
You don't stop riding when you get old, you get old when you stop riding!
1939 Panther 600cc Single - Stolen, 1970 Suzuki 50cc - Sold
1969 Triumph Bonneville 650 T120R - Sold, 1981 Honda CB750F - Sold
1989 Suzuki GS500E - Sold, 2004 Suzuki GS500F - Current ride

sledge

I had it written down in my old shop notes but I think its in Haynes......the `08 version.


SK Racing

Quote from: sledge on January 19, 2022, 12:52:45 PM
I had it written down in my old shop notes but I think its in Haynes......the `08 version.


Just as well, because I would never have looked in the '08 manual.  :thumb:
You don't stop riding when you get old, you get old when you stop riding!
1939 Panther 600cc Single - Stolen, 1970 Suzuki 50cc - Sold
1969 Triumph Bonneville 650 T120R - Sold, 1981 Honda CB750F - Sold
1989 Suzuki GS500E - Sold, 2004 Suzuki GS500F - Current ride

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