77-79 GS550 Petcock - diaphragm & rebuild?

[Chuck78]

Seeing as how the 77-79 GS550 petcock is a one model only item, there do not seem to be any full rebuild kits out there for them.

My friend has a 78 550 project bike, and the petcock always felt very stiff and gritty, did not want to move very well compared to my new OEM. He is on a budget with just starting back to college and supporting his household, and now his diaphragm seems to have failed.

Surprisingly, all rebuuld parts are available from Suzuki EXCEPT for the diaphragm.
Has anyone ever rebuilt one of these and found a K&L diaphragm that worked?

There is this, K&L part # 18-6637:

https://www.ebay.com/itm/292666535443

Which says it fits a 1980 GS550, 77-79 GS400/425, 77-79 GS750, & many other various GS models.

I told him to try and save up for an oem petcock, which is about $97 plus shipping, shopping for the cheapest price around new but that is tough on his current budget. nothing on eBay as far as 77-79 550 kits or aftermarket direct replacements, and absolutely no generic aftermarket petcocks available for this model on Z1 Enterprises, unlike the 750 and other GS models, which seem to have a wealth of various aftermarket petcocks in the OEM configuration. The 550 has a more compact frame than a 750 or 1000, and therefore the hose configuration is different to avoid interference with the carburetors.


I was hoping that the diaphragm was fairly common across various models. I suppose I can take this one apart and find out here, but was hoping to have a definite solution planned out quickly, and hopefully it would be the affordable one of a rebuild.

Thanks,

Chuck

[Gorminrider]

Did you try georgefix?
here's a link of the search I did there for "gs550 petcock"

http://www.georgefixs.com/search.php?Search=&search_query=gs550+petcock

[Chuck78]

I definitely acknowledge that many people have had problems with the K&L petcock rebuild kits, I believe it is in the thickness of some of the rotating parts that does not work out well, but since all of those are available OEM, that is an obvious answer, but the diaphragm is not available OEM.

[Gorminrider]

you should measure that one because they come with various dimensions-that's been my bane, anyways.....but-I think it might be the o-ring on the plunger that is causing some problems. It's the one thing I've noticed that can be a cheap fix....maybe the kits fit too well and stick...but I've never bought a kit or a diaphragm...for lack of being sure of the right diaphragm to buy (measurement-wise) I've made an emergency diaphragms with dollar-store nitrile work gloves and re-attaching the plunger that is still hanging in there. I think it's not too likely the diaphragm itself causing stiffness because even a thick home-made one cut out of a fuel-pump's rubber works...but is too thick to be happy with the screws that hold the petcock together and wasn't quite big enough to cut the right size out of...enough about my thriftiness problem but the oring is definitely something cheap to try for your friend..

and the petcock always felt very stiff and gritty, did not want to move very well compared to my new OEM

[Chuck78]

I have not gotten over there to troubleshoot the bike firsthand, but it sounds like it is starving for fuel, and I knew that previously the lever on the fuel cock was very stiff and gritty feeling. Now, he says he can't get it to run, when he can get it to start, it will spit and cough and backfire, but when he pulls the choke on further it just kills it.
He has had some issues with poor idle and coughing / sputtering / hiccups out of the pods. I set the carbs up fairly well at first, and then after a few weeks of riding, his idle quality went south, and he started having a lot of hiccups out of the pods. I re-tuned the pilot fuel and air screws, and he said it wad the best it had ran in a while. Then he said it started the popping/sneezing/hiccuping again after we did a 4 hour ride with a lot of high speed/higher rpm use. On his way home it started the idle issues again, popping/sneezing/hiccuping out the carbs after a gas stop by his house. Now it wont start up well and wont stay running.
I'm fairly certain that the diaphragm may have failed and is causing it not to open properly (or the o-ring on the diaphragm, which I now see is also unavailable OEM...
My remote guessing is that it is not letting fuel in, and also potentially flooding carb number three.

[Chuck78]

So is it the O-ring on the diaphragm plunger that is the problem that people complain about in the K&L kits, which causes them not to work after a rebuild?

[Chuck78]

I inquired with GeorgeFix.com, and he had nothing to fit the 77-79 GS550.
The center to center bolt spacing is 44mm as with many other Suzuki GS fuel cocks (some are 50mm), but the hose orientation is different. The fuel nipple points directly inboard to the right, & the vacuum nipple points forward at a slight upward angle:



The 1980+ GS550 must have the petcock mounted in more of a rear-mid position on the tank, as both hoses exit rearward on those. That could possibly be made to work if there is no frame interference, but the OEM being only $45 more is definitely an assured fit.

I have a 750 petcock rebuild kit. I may tear apart his 550 petcock and see if the 750 diaphragm fits the bill, and inspect the 40 year old original at minimum.

[hannibal]

I bought a K&L petcock from Z1. Both the fuel outlet and the vacuum inlet point to the back of the bike. I rotated the rear cover to face forward so the vacuum line works like the original and I'm running a slightly longer fuel hose to reach the rear facing outlet. Not pretty but it works.

[KEITH KRAUSE]

If Pingel makes a fuel valve for the 550, I'd buy it and forget it. Not cheap, but they work.

[suzukizone]

So is it the O-ring on the diaphragm plunger that is the problem that people complain about in the K&L kits, which causes them not to work after a rebuild?

FWIW. Some years ago I thought it a good idea to replace the diaphragm on my '81 GS850G with the K&L item. I figured it was cheap enough and with the age of the rubber a good preventative measure. It failed to shut off the fuel supply. I sent it back for a second one. Same problem. Had a good mechanic check my work. Same result. Replaced with the old original diaphragm which wasn't that pretty looking but now at least 10 years later still working after 38 years. Scientific study?....nope. Personal anecdote?...Yup.

DH

[Big T]

Cap off the vacuum port on #3 carb, use prime as On.

Take the lever out and clean the petcock to take care of the gritty feel. If you have mint oil, soak the O ring and the disc. Cost, less than a dollar.