Piston Lift Control System

[dropbear]

Hello,

New to the forum and first post. I'm in Sydney Australia. I rode bikes for 30 years and I'm now coming back after a 20 year break. I'm mechanically savvy, having rebuilt several bike engines and self taught modern auto electronics with cars, but my bike experience (riding and mechanical) is old school - my last bike was a Yamaha TX650. Side point, I recently discovered with horror that bikes I sold for next to nothing are now valuable collector items and wish I had hung on to some.

I hope someone can help solve this mystery. I bought a GS500 2007 not running and unregistered last week. It had been garaged 2 years and after new battery, fuel and carby rebuild and a few other things, it's running well and off to inspection and registration later this week. In the process of pulling the carbs, I found a part (first picture) screwed to the bottom of the right carby, which is not otherwise connected to the carby or anything else. It has a wiring connector (second picture) not connected to anything and no free connector to attach it, but there is a suspicious wire cut (second picture) right where such a connector would be. The Haynes manual refers to a piston lift system solenoid, but I can't find any reference in the manual or Google to what that is. Maybe some sort of disconnected new rider restrictor?

Any ideas what this is?

[sledge]

3 way solenoid port
Part of the emissions control system which is obviously missing!!
Probably removed by a previous owner.

[dropbear]

Thanks Sledge - that's very helpful.

I'm inclined to leave this alone. The bike has been running like this for at least 8 years and in the meantime has been sold second hand by a dealer and passed registration inspection each year. However, I'm curious how this is supposed to work, especially on a non EFI bike without ECU.

I thought we didn't get the PAIR system in Australia, but the Suzuki parts diagram shows a "Valve Assy, Solenoid" mounted in that position and a still available spare part (but AUD95). I can't find an Australian model wiring diagram, but the US and UK ones in the Haynes manual refer to a "solenoid" wired in between the ignition module and coil, the colours and location matching the cut wires in the picture. How would this work - the 3 way solenoid port is linked to coil activity? Sledge's picture shows 2 ports which appear broken off on mine. Where would these connect? What would they do?

[mentalshark]

From what I have gathered, the control unit (which has a throttle position sensor, coil timing, RPM, and other data) controls the solenoid to disable the plastic part from lifting(passing vacuum into the top of the carburetor, opens the gate that lets air into the diaphragm, therefore, diaphragm cant be sucked up) which I have no idea what it does in what situation.

[dropbear]

Thanks mentalshark.

So this bike does have a (sort of) ECU, for ignition, if not fuel/air mix! Despite being fairly old school itself, this bike has a lot of advances on what I'm used to.

The control unit and TPS are intact and the solenoid (off bike now) is identical to Sledge's pic, save for damage to the 2 hose connection tubes on left. I also found vacuum hoses the right size above the carburetor cut and terminated. Looks like the wiring and hose connections to the solenoid have been cut, but the solenoid itself left on the bike. Factory? Previous owner mod?

I intend to leave this alone, as the bike seems to be running fine. Am I missing anything, apart from this bike not having optimal emission control?

[Bluesmudge]

My bike is set up similar to how you are describing. The solenoid has been unplugged and seems to run as good or better than having it plugged in. AFAIK, there is no performance benefit to having it. Seems like preventing the carb slides from lifting in certain scenarios is meant to lean out the mixture under certain circumstances for emissions. If you have an aftermarket exhaust and/or air filter its easier to tune the bike if you remove some of these "black box" emission controls. There are enough variables in a carburetor as it is.

For awhile I have wanted to see if the '01/'02 carb diaphragm caps fit on the '04+ carbs to complete the solenoid removal by removing those white cap things.

[dropbear]

Thanks everyone. It passed registration inspection, so I'm leaving it alone, things having been learned about emission reduction systems.

Today was fun. I rode it to the mechanic doing the inspection, not far, but heavy Friday afternoon traffic on major roads. I haven't ridden on the road for more than 20 years. My only riding in that time has been trail bikes with my brother on his cattle property. He's always keen for helpers to patrol/repair fences. I was crapping myself at first, but this is a very forgiving bike and I was fine by the time I got home. The biggest issue was too many years driving an automatic car and having no real feel for required rpm or gear change timing. The people saying its soft in the front are right, but I can tell already this is going to be a great commuter.

[dropbear]

I've found the answer I think, after being put on the right track by helpful comments from Sledge, Mentalshark and Bluesmudge.

The solenoid is part of a piston lift control system, used by Suzuki on various bikes, not just the GS500. In fact, the same solenoid part number is specified for other Suzuki bikes.

Apparently it's more about noise control than emissions control, the system using air pressure to delay/restrict throttle response in low gears. I guess the intent is to quieten the bike when working up through the gears from stationary.

Disconnection is pretty simple and seems to be exactly what the previous owner of my bike has done; cut and seal the hoses connected to the solenoid and cut the wiring connection. However, my previous owner has done a pretty slack job; breaking the hose fittings off the solenoid when removing the hoses and not taping the cut end of the wiring connection (potentially permitting a short). Bluesmudge refers to capping the hose connections on the carburettors, which would be the right way to finish the job and I've heard that you can buy these caps online for certain Suzuki bikes, but I'm not sure if this extends to the GS500.

Disconnection apparently has no adverse effect on performance and would make the bike quicker off the mark, so it's no surprise that people do this. I'm a bit concerned about legal/insurance implications, so I've bought a second hand solenoid from a wrecker to put on the bike if I ever need to (in case in the future they become unobtainium), but will otherwise leave it alone.

[sledge]

Nah......It might reduce noise to a small degree but the system the solenoid is part of is all about emissions.

http://gstwins.com/gsboard/index.php?topic=57529.0

[dropbear]

Thanks Sledge. Glad I ran this past the well informed. I know an XF650 rider who thinks he's made a performance mod.