Dies at idle after warmed up

[glstine]

I have been riding my '80 GS550L since last February and it has actually been running quite well, until yesterday. I hadn't ridden the bike for 1-1/2 weeks until yesterday. The ride into work was fine. On my way home for lunch I was sitting at a stop light and it just died like someone had hit the kill switch. I hit the starter and she fired right up.

On the way back to the office and then on the way home for the evening I had the same thing happen a couple of times. And then again this morning.

It seems to happen after the bike is warmed up pretty well (after a mile or so of riding). If I keep some throttle on it stays running. Idle is set to 1000 rpm +-, if I set it higher it tends to hang a little before returning to idle.

Any suggestions? The only thing that is different is it sat for 1-1/2 weeks which is the longest it hasn't been ridden since I got it back on the rode and its also the coldest weather it's been ridden in (if that could have an affect) mid 30's-40's.

[Nessism]

You didn't mention if the maintence is all up to date: carbs clean with fresh o-rings installed, fresh O-rings on the intake boot pipes, valves adjusted, petcock functioning correctly, etc.

A hanging idle is a bad sign and shows the mixture is lean. Most likely the carbs are drawing false air from the intake boots, or the pilot mixture screws are in too far. I suggest doing all the basic maintenance first, and then tweaking the mixture screws as needed to achieve the highest idle speed. If the bike still has issues after that, you have at least established a baseline from which to work from.

[glstine]

Prior to February and getting it back on the road - Carbs torn apart, dipped, new o-rings. New intake boots and o-rings, and valves adjusted. Also new spark plug caps and the spark plugs were gaped and looked new at the time. New r/r, new battery and coil relay mod.

I've put on about 3500 miles since then and it's been running good. With the idle set at about 1000 rpm or lower it drops back to idle instantly when the throttle is blipped. When set higher it more like fades back to idle, perhaps hangs wasn't such a good term.

I should add the carbs have only been bench synced, a proper sync is on the to do list as soon as I can get a gauge.

[paco13]

Since it does it when warm, and adding a bit of throttle helps I'm thinking a rich condition. Because it happened all of a sudden after running fine I would first think maybe a spec of crudd found its way to a needle, holding it open a bit causing a rich mix. Could be the petcock went south letting fuel into vacuum hose. Or maybe your choke linkage is sticking.

[Nessism]

I'd vacuum sync the carbs and then play with the pilot screws some to achieve the best idle.

[glstine]

Running rich could be correct, I hadn't thought much about it, but the exhaust last night when I pulled in the garage had that rich smell to it. I am curious though, why would running rich cause it to die at idle (and it dies like the kill switch was hit, doesn't sputter and die).

I was going to do some tweaking in January, guess I will move that up and see what I find.

Thanks for the replies.

[79FiveFifty]

flooded carbs if you're running rich enough to stall at idle, possibly sticking float needle / debris behind needle not allowing it to slide all the way in - pull plugs and have a look see if / which plug(s) darker than the rest

[xxspikexx]

sounds similar to how mine is behaving but im still tooling with it.. a colortune isent a bad idea then u can see whats happening inside you combustion chamber ie running rich/lean. less guess work. as far as syncing like said b4 a good bench sync sometimes is better.

[chef1366]

The cooler temp may be why.
First adjust the idle mixture screws the highest rpm method and then vacuum sync.

[glstine]

Ok I really messed something up this time. I pulled the plugs and they were a nice tan color so it didn't appear to be running rich. Took the carbs out and there was find debris in them so I figure some jet somewhere probably got clogged (I guess I didn't get the tank as clean as I thought I did).

So I took all the carbs apart and dipped them for a couple of hours in Berryman's (I did the 24 hour soak thing less than a year ago so I figure a couple of hours was probably good). After dipping I blew every passage I could find out with carb cleaner.

Put everything back together and tried to start her. Only got a click at the solenoid. Long story short, I ended up replacing the starter with one out of a GS850 project I just picked up (I'll tell y'all about that later). Needless to say this involved taking the carbs out a couple of more times (tried cleaning the original starter, but that didn't work I think the brushes are to far gone).

Anyhow, after replacing the starter and getting the carbs back in again I get her to start and she is running really really rich and will only run for a bit until she dies (I presume from being flooded). After numerous changes to the idle mixture screw and idle settings I would find the plugs either black or wet (at one point fuel was spraying out the exhaust). I've got good spark (at least I think so, I don't really know what it should look like but I can see it with the fluorescent lights on in my garage).

So I imagine I must have done something wrong with the carbs. What are the things I should look for? Most obvious to me is float height, but I double checked those and had them set at about mid-height based on the Clymer manual.

Thanks in advance.

(BTW - I did put a fuel filter back on, making sure to route the line so it didn't hinder fuel flow)

I should also add it starts right up from cold with no choke, which hasn't ever happened before.

[chef1366]

It's hard to get too much fuel with the right jets unless the floats got out of adjustment or a float needle is sticking.
What is your voltage at the coils? A weak spark can cause a mock rich conditioin.

[glstine]

I have stock jets. I haven't measured voltage at the coils, however, I did the coil relay mod a few months ago so I would imagine that's not the problem, but I will check that before I take the carbs out again, maybe I'll get lucky and won't have to take the carbs out, again.

[glstine]

I am now at a loss and don't know where to go from here. What I've done:

Tested voltage at coils and have only a 0.1V loss from the battery.
Checked spark on all 4 plugs.
Checked valve clearances, was tight on three valves so changed out the shims on those.
Checked cam chain to make sure it hadn't jumped a tooth at some point.
Tested compression and got 135, 135, 130 and 140.
Took apart the carbs, dipped, replaced O-rings and reassembled.
Intake boots and O-rings are less than a year old. I set the floats at the maximum height to have the lowest gas level in the bowls.
Jetting is stock and airbox and filter are stock.

Since I put the carbs back in it starts easy but was running really rich it would seem (particularly on #4 cylinder, I have turned out mufflers on each pipe and the #4 pipe has white smoke and the pipe walls get damp with I presume gas). It would start and idle however as soon as the rpm's would hit 2000 it would die. I had set the idle mixture screws at 1 1/2 turns out (or so I thought, more on that later). Checking the plugs, #1 was black, but dry. #2 was wet but not really black. #3 was a nice tan color. #4 was black and wet. Not knowing where to go I thought I would experiment with the idle mixture screws and start with just seating them all the way and start backing out slowly.

I started with #4 and looked at the screw and it appears that there was gas on top of the screw. I went to turn it in and it went quite a few turns in before it seated so I obviously didn't get that one set at 1 1/2 turns like I thought. So I decided I would start over on all of them and set them all to 2 turns out. I started her up and she started fairly easily (not as easy as before though) but will only run for a few seconds and then die. In attempting to get her to run had a couple of really loud backfires including sparks flying out of the #4 pipe so I decided it was time to seek help. I did check the plugs one last time and #1 and #3 looked good, #2 was wet but not black, and #4 was kind of wet, but not black.

I don't know where to go from here. Any suggestions would be greatly appreciated.

[paco13]

Check that your plug wires are on right, 1/4 fire from same coil, 2/3 from other.
Did you have all plastic bits and orings removed including the ones on needle valve before you dipped carbs?

Black wet plug, white/blue smoke, and wet residue in pipe sounds like oil burning.

How is the oil, level,smell?

did you check compression after valve adjust or before?

[Nessism]

Did you take the bike out on the road or are you just running it in the garage? If in the garage, you can't judge that way. Set the mixture screws to about 2.5 turns, do a vacuum sync if you haven't already, and then take the bike on the road if you haven't already.