So I'm still getting to grips with the joys of mechanics. It started as a random idea and evolved into a garage full of bikes and cars and many evenings teaching myself all about them. I feel I've learnt a lot but still quite a novice. I've had success with restoring an old '94 Triumph Daytona, so thought I'd go in for a full on rebuild on two GS500s that fell into my lap. I've always had a sweet spot for the little twin, never look like performers but in the right hands they can show up the bigger bikes, and nothing is better than the look on their faces as you fly through a corner past them 

The majority of the bikes were either in boxes or rusted up and full of spiders and thorn bushes so there was a lot to do. I've rebuilt/replaced/de-rusted/repainted pretty much everything and the bikes are so close to being completed but I've hit a stumbling block on both. The fuelling. I've spent weeks reading through the manual, reading through threads on here and anywhere else and I've got nowhere. I want to be able to say I've fully built the bikes myself but I'm in need of expert help.

My '94 Ocean Blue is what I've been trying to solve this week. When I got this around a year ago I managed to get her running before going into the detailed rebuild. From the top with the fuelling; the tank is clean and the petcock nearly new and working. Fuel is flowing through the hoses into the fuel tap, this was taken from a working donor bike as my one had blown the diaphragm. The carbs have been cleaned and refurbished, nothing blocking the needles and o-rings/seals all present and correct. Floats have been checked and adjusted to manuals specifications, when hooked up float bowls filling and shutting when they should. Electrics all work. For some reason it seems to be starving fuel and I'm stumped as to what is causing it. If I spray some beaded into the airbox it starts fine and dies. I've gotten it to fire up a few times but it'll die after a few seconds. I move the fuel tap from prime to reserve and on, seems to work a bit and then die again. It's like it gets a bit of fuel and then once it's run out it's dead again. Is there something simple I'm missing? Have I missed a step? I want to get out and ride her, seems so close but yet so far!

Any pics you can post of how it is all set up? I dunno if you can do that. Just thought it might point something out. Obviously, vacuum line hooked up, sure hoses are routed right, nothing stupid like pods on them right, uhm,... Trying to think what else I'd check,...

Hi, haven't got any pics at this moment in time, will have to get out to the garage in the day after work and get the airbox off to show the hoses. Fairly certain the lines are all in the right way, always made sure I only pulled apart one bike at a time so I had a point of reference Incase I couldn't remember how it went back. No stupid pods, keep it original. Why change what works, or not in this case 
I've been scratching my head for a long while on this! Found a carb rebuild kit for £14 so I'm thinking to get one and just take everything apart and put together again just on the off chance I busted any of the needles or rings when I put in the last kit perhaps? Thinking for a few quid it's worth a shot, and if not then it'll at least narrow down the cause. Wanted to keep the bikes original but I can see why a lot of people change over the fuel tap as the system seems over engineered!

Could be a gross vacuum leak somewhere causing insufficient vacuum at the petcock. Common places easily overlooked are the o-rings under the vacuum ports on the carb top covers, or maybe the caps over those vacuum ports are missing? maybe the vacuum line to the petcock is connected to the wrong carb? Both have a vacuum port on them but one is blocked internally. if you had a vacuum pump you could apply vac to the petcock vac port and determine if that's the issue.

However, IME even with the petcock nerfed if you put it on PRI it should run, and if the carbs have fuel in the bowls then it will run a few minutes even under load (riding through the neighborhood) before the carbs run dry. So if it's not running but for a minute even with the float bowls non-empty then it would seem that you might have one of the following:
- blocked/clogged pilot jet or pilot jet fuel supply orifice
- blocked/clogged pilot air orifice (it's in the throat of the carb, tiny hole)
- pilot needle (aka "mixture adjustment screw") assembled wrong, o-ring missing, o-ring/washer/spring in wrong order, etc. so that the fuel leaks down the needle rather than going into the jet
- bit of (or entire) old o-ring stuffed in the pilot needle hole blocking fuel delivery

BTW you can check out my infamous blog post which might help:
https://joshkarnes.blogspot.com/2017/09/fixing-common-gs500-carburetor-issues.html

But I would say this:

with fuel in the float bowls, idle "speed" screw backed all the way out (minimum), "choke" jet not clogged, choke engaged and working, pilot jet not clogged, pilot air orifice not clogged or blocked, and pilot needle assembled right with a fresh o-ring and backed out 2.5 turns, THE BIKE WILL START AND RUN. If not, then the problem is not in the carbs. It will run long enough to deplete the fuel in the float bowls, which is minutes.

If you verify all of this and it still won't run, I'd say maybe check compression, spark, maybe bad coils, bad ground, maybe cam timing is wrong, etc.

Thanks for the response, with what you've said in mind I think it's worth me getting another new pair of rebuild kits, pulling it all apart and starting over. The tops of carb caps and o rings around them are all ok so I think it may well be the latter.  Funnily enough I've got your post as a saved bookmark for reference, so will take another read tonight, but what you've said is very helpful so I'll replace and set up as you've said and see how it goes.
I know at this moment the compression is all ok, spark is good and coils are fine, but fingers crossed it'll be fixed before it gets that far 

I read his carb write up before I knew he wrote it.  Good stuff there.

And I'd said stupid pods cause mine came with them and after really having a tough time with a xs400 with pods, I'm not a huge fan.  I think you'll figure yours out here real soon.  Sounds like you have a good understanding of everything and the motivation to get it going.

I wrote that up after struggling through my own work the hard way and sifting through the mass of very durable misinformation all over the internet (like, "hanging idle means it's running lean", "with bigger intake and exhaust, you need bigger jets because it needs more fuel to make more power", "vacuum leaks mainly affect idle" and other hits!).

So far it seems like many people have found it useful! I even see others on this forum pointing people to it. Warms my heart. And hopefully makes people's GS500s run a little better and with less trouble.

It gets shared pretty often on the Suzuki GS500 facebook group too I know it has helped many people!!!

there's a facebook group? who knew?

I'll have to look for it and join! Didn't even think to check Facebook! So I've ordered new kits, thought I'd get another new one for the other bike as they were so cheap.
Took a couple of pictures now I've been out and taken off the airbox, no idea how to post them but will explain the hose layout just to be certain I've not been a complete novice with it all!

So from the fuel tap I have four hoses, narrow hose on the back I believe is the vacuum which is connected into the top of carbs near the choke rail. It's connected to the left carb if you're looking from the back of bike towards the front so it's routed pretty much inbetween the carbs.
The central hose which is the main fuel line?, goes into the bottom connector inbetween the carbs, with the top connector being the breather hose that effectively doesn't go anywhere?
Then the other two hoses on the fuel tap are the main fuel line and reserve line that feed back up to the petcock in the tank?
Looks like it does in the Haynes manual so I'm hoping I've not made a gross error there that's causing the problem.
Hopefully the kits will arrive Monday/Tuesday so I can then update further once I've stripped them and swapped it all over, guess I'll have to find something else to break over the weekend 

Forum has lots of great stuff on there.  I was looking for a post (i think) Bri,...errr Show posted on the lines but I can't find it.  Somewhere somebody said that the manual had the lines wrong in the diagram.

That is right, most of the diagrams are wrong (I think the ones in the manual and on OEM parts sites). Here's the wiki link with really helpful and corrected diagrams. They can also be found in the Files section in the facebook group

http://wiki.gstwins.com/index.php?n=Main.HoseRouting

Quote from: mr72 on September 20, 2019, 05:18:05 AM
there's a facebook group? who knew?

What's facebook???   

Another path you may consider - vacuum leaks can be the bane of any carb system. 

It's possible to take off all the accessory vacuum lines, including to the petcock and PAIR/secondary air.  I mention some of it in my build thread, and there's also tons of other threads about it.
Maybe also check that that your fuel tank is properly vented.  This can cause fuel starvation during riding, but doesn't sound that you're even at that point yet.

Good luck!

Update time! Finally a day off work and the carb rebuild kits arrived so overhaul time. I carefully took apart everything and didn't find anything looking old, knackered or in the wrong place. Still continued with removing everything, gave it a good spray of carb cleaner for good measure and replaced everything with the new kit. Checked pilot screws set up correctly and floats at right height and stuck back together with my fingers crossed!
Hooked it all up and success! No idea what piece was causing the issue as nothing looked off, but it's back to life and I'm now one happy man!
Now for the rain to stop and I can take it for a spin 

Sweeet!  Can't wait to see some out and about pics!

Hopefully will get some soon! Had her running, blowing out all the crap that was in her, started off not wanting to go when twisting the throttle but is getting better. Fresh fuel and running much better.
Few little issues that needed addressing before its MOT, front brake wire had got caught on frame and split, forks were weeping and rear brake calliper leaking but all sorted so fingers crossed she'll have her MOT within the week!
Now onto number two, bought another carb rebuild kit and thought I'd just overhaul it again to be safe, seems to have worked on number one so no harm. Just finishing off putting her together and will see what happens. Fire extinguisher at the ready