09 GS500 stumbles when accelerrating

[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,..

[mr72]

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

[motoitalia]

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.

[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

[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.

[sledge]

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. 

Btw, is it mentioned in a manual somewhere?

[sledge]

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

[SK Racing]

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.