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Bike won't idle

  • Thread starter Thread starter glenwill
  • Start date Start date
G

glenwill

Guest
I'm putting this in Electrical/Ignition, but I don't know where my problem is, so this could be the wrong section.

I have put about 400 miles on my GS550L since I Kreem'd my tank and rebuilt my carbs (with new o-rings, dipped, thoroughly cleaned), and up until now the bike has been running great. When I did the carbs, I also replaced the petcock and all hoses, the intake ports and o-rings, the air filter and the spark plugs. I then adjusted the air screw for smooth idle. As I said, it ran fine for about 400 miles after this.

Suddenly this week, it won't hold idle for more than a couple of seconds. I can start the bike with the choke pulled, and as long as I leave choke on, it stays running. As soon as I push in the choke, it smooths out for a second, then begins sputtering and dies within 2-3 seconds.

I checked all 4 cylinders for spark, and all four seem to spark fine.

I don't know if this is relevent, but after running the engine for a couple of minutes, I thought maybe I could tell if one cylinder wasn't working by checking the temp of the exhaust headers.

Using my infrared meter I get roughly the following:
Cylinder 1: 100-110
Cylinder 2: 200-210
Cylinder 3: 210-220
Cylinder 4: 150-160

Cylinders 1 and 4 are both low, with 4 being very low. Does this indicate what might be wrong? Are cylinders 1 and 4 on the same coil? If so, that might indicate a problem with the coil.

What should I check next?

Glen
 
Since you said it had good spark on all 4 , I'd suspect 2 or more plugged idle circuits- using choke is compensating for a lack of mixture at idle. Maybe, the Kremed tank is shedding something
 
I had pipe temp's all over the place, until I did a bench sync with a piece of MIG wire.
after that they were all within 10 degrees of each other.
Well, for a few thousand kms anyways, then I got mismatched temps and rough idle after pushing in the choke (off).
So I pulled the carbs, did a compressed air cleaning and re-bench sync'd them and every thing was back to normal again for a few thousand more kms.

As for coils make sure they are getting at least 12v to the terminals.
Anything less will affect performance I believe.




Tank
 
Hi,

Is the petcock operating properly? Is there a leak in the vacuum line from the #2 carb to the petcock? Are the float heights properly set? Have you done a close visual inspection of the air intake system to look for air leaks? Are the intake boots and intake O-rings new-ish? What is the voltage at the coils? I also agree that it could be something from the gas tank got into and plugged up the carbs. It's going to be a process of elimination. :(

Recently my bike was acting weird, wouldn't hold a steady idle and wanted to die. I kept adjusting the main idle knob, idle mixture screws, choke and throttle cables, etc. Upon a close visual inspection I found that the airbox had crept back away from the carbs and had pulled a couple of the 'airbox-to-carb' boots off of the carb intakes just enough to cause air leaks. I loosened everything up, put it back in place, tightened the carb clamps, etc, and it idled normally again. Then I had to re-adjust everything once the air leaks were gone. Now my Jessie is running like a champ again. ;)

Thank you for your indulgence,

BassCliff
 
tom203 said:
Since you said it had good spark on all 4 , I'd suspect 2 or more plugged idle circuits- using choke is compensating for a lack of mixture at idle. Maybe, the Kremed tank is shedding something
Click to expand...
Hate the thought of ANYTHING getting into my nice new rebuilt carbs....thats why I started using an inline filter for the first handful of tanks or gas I run after any fuel system work.
I had a thouroughly cleaned tank and new lines and what not and was surprized at the micro sediment the filter picked up. dont want that in my carbs.
I use a 3.88$ Fram filter from wal mart. They are a bit bulky, but only temporary. Paper element catches more than the plastic screen type, I even had the pourous stone type and found sediment in my down stream clear fuel line.
Not saying this is your problem, just sharing.
 
How long had it been since the bike had been started ? Sounds like the pilot jets have become clogged, the ones under the rubber plugs....
Just pull the carbs, pop off the bowls, get the jets out and dunk them in a small container of carb cleaner for awhile. Make sure you can see light through them when you're done. :)
 
Thanks for the replies. The bike has not sat at all. It's had been ridden every few days since I did all the work to get it running. I did bench sync the carbs when I did the work on them.

I have confirmed that the intake boots on both sides of the carbs are fully sealed and the clamps are tight. I also confirmed that the vacuum hose and fuel hose are both on tight.

I guess I'll check the air box and air filter, then the voltage at the coils, and then pull the carbs.

If the coils were not getting enough voltage, or if one of the coils was going bad, would it likely have problems at idle, but rev up just fine?

Would pix of my 4 spark plugs be helpful in diagnosing?

Glen
 
Needless to say, the carbs should be vacuum synced and the valves adjusted before you can diagnose running problems. Coil voltage is a good place to start after you complete these tasks.
 
Nessism said:
Needless to say, the carbs should be vacuum synced and the valves adjusted before you can diagnose running problems. Coil voltage is a good place to start after you complete these tasks.
Click to expand...

Thanks Nessism. The valves were adjusted. I have been wanting to vacuum sync, but haven't gotten around to buying the tool. But before I can vacuum sync, shouldn't I have a bike that can hold idle first? My understanding is that the vacuum sync would be done with the bike idling.

Glen
 
glenwill said:
Thanks Nessism. The valves were adjusted. I have been wanting to vacuum sync, but haven't gotten around to buying the tool. But before I can vacuum sync, shouldn't I have a bike that can hold idle first? My understanding is that the vacuum sync would be done with the bike idling.
Click to expand...
True, but if the carbs are not properly synchronized, it won't idle properly. It's a bit of a viscious circle.

The bench sync that you did was just to get them close enough to be able to start the bike and get it warm enough to do the vacuum sync.
Apparently you felt that going through only half of the procedure was enough. You are now finding that "shortcuts" are actually "LONGcuts". :o

.
 
I actually didn't realize the vacuum sync was critical. I thought that since the bike was running well, it was a low priority until I was ready to spring for the tool.

Would pix of the plugs be helpful in diagnosing the problem?

Glen
 
I measured the voltage today. I have 12.4 volts at the battery, and 10.5 volts at the connector right before the coil. This is with the ignition on but the engine not running.

I'm assuming this is a problem. Is there a component between the battery and the coil that could be faulty? Or is this mean a problem with dirty connections somewhere along the way?

Tomorrow I was planning to trace the wires through and check every connection in the path to the coil.

Glen
 
Usually dirty/corroded connectors and the ignition switch contacts.
 
I went through all of the connections, and found several connectors that were badly corroded, and some that were blackened from arcing. I cleaned them all up. I also took the plugs out and checked compression. I discovered that the plug in cylinder 1 had much too small of a gap It was sparking, but probably too little. That might explain that cylinder running so much cooler.

I put it back together, started it up, pushed up the idle a little and readjusted the air screws. It's running great now, holding idle fine and running well. Thanks all for your help on this.

When I did the compression, here's what I found:
Cylinder 1: 95
Cylinder 2: 120
Cylinder 3: 90
Cylinder 4: 90

Is this a problem? On another thread where someone posted similar readings, someone said that after adjusting valves and carbs, ride the bike and the compression will come up. Is this true?

Glen
 
How you do the test will affect the outcome. The correct method is:
Warm engine
Throttle fully open
All plugs removed (spins easier)
Hit starter button until gauge stops incrementing
Take reading.
Is this the procedure you followed?
 
koolaid_kid said:
How you do the test will affect the outcome. The correct method is:
Warm engine
Throttle fully open
All plugs removed (spins easier)
Hit starter button until gauge stops incrementing
Take reading.
Is this the procedure you followed?
Click to expand...

Oops. I forgot about WOT. I did the rest. I'll do it again tonight with WOT and post the results. Hopefully it's better.

Glen
 
OK, I retested using the procedure koolaid_kid outlined: warm engine, throttle fully open, all plugs out (I had unplugged the connector feeding the two coils).

Now I measure:
Cylinder 1: 130
Cylinder 2: 120
Cylinder 3: 120
Cylinder 4: 130

2 questions from this result:

1) Are these readings good? Borderline? I read they should be within 10 psi of each other, which they are.
2) Why would cylinder 2 measure 120 both with the throttle closed and open? Where as the other 3 were much lower with the throttle closed. Does this suggest carb 2 may be adjusted wrong so that it is open somewhat at idle?

Glen
 
glenwill said:
2) Why would cylinder 2 measure 120 both with the throttle closed and open? Where as the other 3 were much lower with the throttle closed. Does this suggest carb 2 may be adjusted wrong so that it is open somewhat at idle?
Click to expand...
One possibility is that you might not have had the vacuum port (to the petcock) plugged when you did your first check, and it was able to suck enough air to give you a better compression reading.

I don't think that the vacuum port will give it enough air to get a full, PROPER reading, but that is one possible reason for the higher reading.

.
 
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