Hi all,
Looking for some ideas/suggestions on my nightmare that is the carbs. Sorry in advance for the lengthy rant!
I've completed a full rebuild on a '93 plate and despite the nice clean mot, I've fallen at the final hurdle with it not running right.
I've thoroughly cleaned out the carbs, made sure no holes are blocked and replaced o-rings and such. I painstakingly set them up exactly how the Haynes manual (floats at 14.6mm, mixture screws 2 1/4 turns etc). Fired up fine, idled fine, revs fine in neutral, but when on the road at anything over 1/4 throttle it would bog down and lose revs. Reading the forums some say running too lean, some say too rich. I checked sparks and they were blackened suggesting too rich, as well as firing up inside my garage it smells heavily of unburnt fuel. Ended up with mixtures at only 3/4 turns. Sparks looked much healthier and bike runs better, but still bogging just at higher revs and slightly further on throttle. If you try to quickly go full throttle it'll initially rev up and then jerk and then bog.
Tried a suggestion by another member to try riding with choke on, if it runs better then that's a sign it's actually too lean. True enough that was the case so at his suggestion I backed the mixtures out 3 turns. Again ran a bit better but still showing same symptoms.
I've since checked many things.
Engine timing. All set up fine
Valve clearances. All absolutely perfect
Air filter. New and not blocked
Vacuum tap. All good.
Fuel tank. All clean and fuel running through fine
Fuel lines. None blocked or pinched
Air leaks around inlets. None at all.
I then tried the float level check with clear hose. Showing it was too low. Good to see the Haynes manual spec is rubbish. Based on the hose test I then adjusted the floats to get them to sit at the gasket level.
After making the adjustments to the floats I've then put the mixtures back to 2 1/4 turns to start again with tweaking. It now is struggling to start, I have to twist on the throttle when firing to get her going and even when idling ok it'll randomly just die. It's now acting like it's flooded, struggling to fire up at all and had a nice backfire that scared the life out of me.
I'm going to put the floats back to how they were as that clearly didn't help, but I'm now out of ideas as to what to do next as it feels like I've tried every avenue other than setting fire to the whole thing and just replacing with another bike that's working!
If anyone has any ideas or has encountered this kind of problem I'd be forever indebted to them. It's so close to being finished, I want to be able to enjoy it!

try this, forget the Haynes manual.

https://joshkarnes.blogspot.com/2017/09/fixing-common-gs500-carburetor-issues.html

It's literally the first hit when doing a Google search.

you probably have bad pilot needle o rings, vacuum leak causing slides to not come up, and leaking intake boot o rings. But who knows. Just fix it all. Btw you can't adjust the mixture by just counting turns, you have to do it with the bike completely warmed up listening carefully for rpm changes. But that doesn't really matter if you have other issues.

I'm about to do a carb rebuild, and these kinds of reports are like hearing the theme song from "Jaws" while swimming 100 yards off-shore...

Check your floats by U tube method. I'm pretty sure one or both are high - likely leaking at the seat. I also don't like the 14.6mm method - cos every one I have worked on that was set to 14.6 was horribly horribly off.
Cool.
Buddha.

yeah it's also very approximate to set where the needle just touches the tab. It's possible to get lucky and set it right, but measuring with a tube is way more accurate.

Thanks for the suggestions, I'll strip them back down for the hundredth time and start again. I've checked for air leaks when running by means of spraying easy start around the rubbers and no change in rpm so all seems good. With the airbox off and having it running the slides go up fine and aren't getting stuck. Also has nice new pilot o rings but I'll swap them over anyway.
Funnily enough I use that blog as reference all the time, worked wonders on my first carb rebuild on my other gs and it went perfectly.
I used the clear hose way to check the levels and made the adjustments whilst I had it off the bike being fed by a remote tank and held up by a vice on my desk.
They looked to be spot on but certainly doesn't seem that way so I'll adjust again when stripping.
I'll update with how it goes next and see if I can ride it for more than 5 minutes before it dying on me

So today's update. I've stripped the bike down and pulled the carbs apart.
All the inner workings all still brand new and shiny, but have opted with giving the carb bodies a nice long bath in a vat of brake cleaner for a few days just Incase there's any bits of crud stuck right up inside them.
While they're soaking I've had a look over everything else in preparation for re-assembly.
Inlet rubbers have no cracks or damage and no leaks. Fuel lines all nice and clean as well as the fuel tank.
I've cleaned up the spark plugs, spun the engine a few times and left to dry the excess petrol out of the engine. Checked the oil and looks good so doesn't appear any petrol has mixed when flooding.
Fingers and thumbs all crossed when putting back together.
And yes Josh's blog is like my bible for all this, think I can almost recite it word for word 

Don't soak it in chemicals. And trouble shoot and do 1 thing - not throw everything including the kitchen sink at it.

Cool.
Buddha.

If you've still got the carbs on the bench, do the float bowl test with the tube method before you put it on the bike.  Just find some way to run a temporary fuel line from above and let gravity do the work.

No reason to install on the bike, just to take them off again for each float adjustment.

Then when you have the carbs back on the bike, I found it useful to run it for a very short time without any air filter or gas tank in the way (again, rig up some temporary but safe fuel supply).  This is so that you can check that the sliders move easily when you twist the throttle.  Also that you've got all the throttle cables well adjusted, without having to fiddle with the gas tank on and off.

Well the bike is more unwell than before. I followed the blog to the letter and no joy. I had previously tried the bench testing method to save having to put everything together and remove multiple times but that didn't seem to result in any success.
If I try to run it without any adjustment it won't run for more than a few seconds before spluttering and dying. Ended up having to turn the mixtures all the way back to about 1/2 a turn out in order for it to fire up and stay running even with the choke on. At that point tried to ride it but it would bog and die and be a little better with choke on so it's like it's super lean.
Try and adjust mixtures back out and rides a bit better but still dying. Trying to run at the side of the road and it won't stay running, took the sparks out and blackened. It's like it runs stupidly rich at stand still and then stupidly lean when moving.
Feel like giving up, such a confidence knock!

Quote from: Carlos13w on June 01, 2020, 11:06:00 AM
Well the bike is more unwell than before. I followed the blog to the letter and no joy. I had previously tried the bench testing method to save having to put everything together and remove multiple times but that didn't seem to result in any success.
If I try to run it without any adjustment it won't run for more than a few seconds before spluttering and dying. Ended up having to turn the mixtures all the way back to about 1/2 a turn out in order for it to fire up and stay running even with the choke on. At that point tried to ride it but it would bog and die and be a little better with choke on so it's like it's super lean.
Try and adjust mixtures back out and rides a bit better but still dying. Trying to run at the side of the road and it won't stay running, took the sparks out and blackened. It's like it runs stupidly rich at stand still and then stupidly lean when moving.
Feel like giving up, such a confidence knock!

you sure both the cylinders are firing up? sounds like not, good spark on both plugs? Just incase if afterall its not the carbs anymore🤗
oh and are the carbs in sync? doesnt have to be alot offsync to not run properly

There has to be something bulk wrong, like the pilot and main jets reversed or the pilot needle/spring/washer/o-ring out of order or the needle hung up on the edge of the emulsion tube so it doen't ever go down...

Or you know a dozen other things. huge vacuum leak, bad rings, mouse in the intake tract...

Yeah both firing up, sparks good, and synced up fine.
It's becoming more and more of an enigma to me, starting to think maybe there's a rat or something living inside it or it's haunted by a ghost?!

Pilot needle set up definitely correct with the o ring the right way round. Nothing sticking, all nice and clean and new. If only it were simple! This is starting to make me lose sleep 

ok, its haunted for sure, the carbs aint that complicated, u sure all fuelhoses are in correct spots?

You're not stupidly lean when you try to ride it - that doesn't happen till you get 1/2 way up the throttle position.
I'll pretty much guarantee you your float level is wrong. Idling at 1/2 on air screw is a dead giveaway.
You're not running 60 pilots ? I don't think so.
You're not running 200 mains ? I don't think so.
You're not running 15 washers under the needle ? I don't think so.
You didn't cram the air screw 13 turns past tight ? I don't think so.
You didn't pull a bunch of those air jets in the bell mouth out ? I don't think so.

You have a fuel tap leak fuel into the vacuum side ? This I don't know - make sure.

Yea that leaves float level.

Cool.
Buddha.

Buddha, going by your reply I've pulled them apart again and checking the floats again. Presumably they were too high?
Keep getting dodgy readings from using the clear pipe method, so I've ended up with it all open using a desk vice and elastic bands. It's messy but I can at least see what on earths going on. I've made a bit of adjustment to make the level lower, so will reset mixtures and see what happens

Quote from: Carlos13w on June 02, 2020, 04:52:20 AM
Buddha, going by your reply I've pulled them apart again and checking the floats again. Presumably they were too high?
Keep getting dodgy readings from using the clear pipe method, so I've ended up with it all open using a desk vice and elastic bands. It's messy but I can at least see what on earths going on. I've made a bit of adjustment to make the level lower, so will reset mixtures and see what happens

Yea explain that please - and IMHO dead giveaway clue - dodgy with U tube = dodgy in real life.
You can eyeball it all you want, remember in real world use it is what it acts like as installed in the bike - not by eyeball.
Leaking float spigot O ring will do exactly as you describe. Perfect by eyeball, terrible when installed and run.

Cool.
Buddha.

So sometimes the fuel in the pipe won't go past the drain screw and you can see a slight bit of fuel around the screw. Sorted that with some trusty ptfe tape. But still, when the fuel starts running into the pipe there's always a huge bubble of air sat between the fuel and the drain. Every now and then it seems to work fine but other times not.
Last time trying it, was showing both floats a little under the gasket level, wanted to adjust a bit lower and then when I checked one went really low and other went higher.
I'll check those o-rings again although they're new so shouldn't be failing.
It's just disheartening that I've spent more time on this one issue than I spent rebuilding the entirety of the bike and don't seem to be making any headway on it at all

You're missing something - really if you were to send me your carbs back in say 2015, I'd have sent you a note with the 1 thing that was wrong. Anyway you will have to find that 1 thing you're off on. My guess was float O ring - but find it and you'd have it work great.

Cool.
Buddha.

I'll kick myself if that's the case, but really at this point I'm really hoping that it is the case. After several pulling apart and faffing today one side looks to be shaping up ok and the other not so. I've looked at the other one for this o-ring, it's new and seems to fit in ok, but it's not quite like the other where the rubber seems to make it too big to sit flush. So I've swapped it out and will see how it goes.