Idling issue's after carb sync

[ccogswel]

What I have is a 80 XS11 all stock. My brothers bike. I got it out this year to get it ready. Went through the carbs to make sure they were clean. Got floats adjusted. Started out with 2 turns out for idle mixture screws. Warmed up the bike to get it ready to sync. Used my carbtune. Got all 4 in sync. Adjusted the idle screws. Then resync. The bike will rev up and come back to idle. But it will only idle for about 20 seconds before it slowly idles down then dies. I've adjusted the idle screw with no help. If I turn the idle screw to much it will hang with a high rpm. But if I unscrew the idle screw it will calm down but then after a few seconds it will slowly die down. You can start it back up with no throttle and it will idle up to 1500 and come back to 1100 and then after like 10 seconds it will idle back down slowly and die. I have checked the sync on the carbs and they are all the same. I've done a carb sync at idle and even tried it at 5000 rpms then checked it at idle and still all even. It has new carb boots. No intake leaks. I'm at a loss. Or maybe I need to take it out for a ride? Anyways I hope to get a few idea's. I know I'm not the only one to go through this particular situation. Any help will be greatly appreciated.

[Bonz]

So it ran last season when you parked it, before the carb work? Sounds like a fuel supply issue?

I assume you used a remote fuel source when you sync'd the carbs, as it must have run continuously and for longer than 10 seconds or so at at time?

Do you have a Standard or Special, your signature does not list an 80 model year bike.

My first guess is the fuel cap vent and other first guess is a pinched fuel or vacuum line. Then possibly the Octy if you have a Special.

[bikerphil]

Check your plug color, kinda sounds like a rich condition. Is your float height set correctly to 23MM?

[Bonz]

That'd be a WAY rich condition... As in drowning... Says he adjusted the floats, so that's why I went the starvation route...

[ccogswel]

It's a special. All stock. The floats are 24. The same setting as last year. As for the remote fuel supply I just turned the tank backwards. Hooked up clear fuel lines so I can keep a eye on fuel flow. The only thing I had noticed was a bunch of air bubbles in the fuel line. Maybe that's it? It ran fine last year. But there towards the end I noticed it was having some idling issues towards the end of season. But nothing like this. You can rev the bike up to redline or even 4 or 5 grand and it will come back to a idle. All the jets for it I got from Mike's xs. Got stock size jets. I'm gonna fool with it a bit more this evening.

[Tat2demon]

If you have the old jets, compare them to the new ones. Some have the wrong number of holes in them and are not recommended.

[Bonz]

Do those jet sizes from Mikes match up to the stock jet sizes?

Maybe the jetting is off if the sizes are not apples to apples?

I recall hearing something about that at one time but I'm not sure?

[Bonz]

I see Tat2 beat me to it, didn't see his post on my phone when I was doing my post. Yeah, check those jets...

[skids]

I would like to what you did to fix it after you fix it.

[BA80]

When it goes to die try pulling the enricher lever out and see if that helps.

Also, according to the manual the floats are supposed to be set at 23mm +/-0.5.

24 should be close enough but could be a little low (lean). Those later carbs are pretty cold blooded I've noticed. Don't run well until the engine is completely warmed up.

Just throwing that out there.

[ManagerMike]

Got all 4 in sync. Adjusted the idle screws. Then resync.

The idle screws are what you are supposed to be adjusting when synchronizing the carbs, not the mixture screws. Go back to two turns out on the mix then get the vacuum levels balanced with the idle screws.
Keep in mind, the idle stop screw thumb wheel adjusts #3 throttle plate, the idle screw between 3&4 adjusts #4 throttle plate relative to #3. the screw between #1& #2 adjusts the relation between those two throttle plates, and the screw between #2 & #3 adjusts the balance of BOTH 1&2 to BOTH 3&4.
Once you have all 4 cylinders pulling equal vacuum, you can then move on to adjusting idle mixtures to your satisfaction, then re-sync the vacuum draw again. Lather, rinse, repeat...

[Bonz]

Most bikes will run even with a crappy Sync... he has an issue with fuel I'm convinced of that. If he adjusted the idle mixture screws to sync and not the sync screws then the fuel could be the issue... but that wouldnt explain why it ran well while sync'ing then went to pot.

[BA80]

Most bikes will run even with a crappy Sync... he has an issue with fuel I'm convinced of that.

Agreed, either too rich and flooding or too lean and starving.

[skids]

I would like to what you did to fix it after you fix it.

Good grief! I meant, "I would like to KNOW what you did to fix it after you fix it."

[ccogswel]

Well I didn't get out there this evening like I hoped. But the jets I got from mikes xs were the real mikuni jets. They had the same holes in the pilots as the original ones. The reason for replacing them was the originals were buggered up so I got some K&L kits I bought years ago but had bad jets. So I got those from mikes. I plan on checking to fuel supply as I had noticed there was alot of air bubbles in the lines. I couldn't see it being that but you never know. And I'm sorry I didn't make myself clear about the adjustment steps I done. I synced the carbs first using the screws in between each carb. Sync 1 and 2 and then 3 and 4 then 1/2 to 3/4 then adjusted the idle mixture screws and then rechecked the sync. All I know is something is not right as I can and have had the idle mixtures screws as far in as half turn out to 3 1/2 turns out and it still slowly idles down to 500 rpms and then just as it gets to about 3-400 rpms it dies.I'm using a new carbtune I bought couple years ago. Maybe I need to check it to make sure it's working correctly? Maybe the sync on it isn't right? Thanks for all the recommendations so far.