Bike won't idle

[glenwill]

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

[koolaid_kid]

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?

[glenwill]

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?

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

[glenwill]

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

[Steve]

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?

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.

.

[glenwill]

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.

.

Hmmm...yes, that's a definite possibility. I did plug it when I was adjusting the air screws, but I don't remember whether I had it in when I did the first compression test. Thanks for thinking of that.

What about the numbers? My Clymer manual says that compression should be 128+, and that less than 92 means it needs a rebuild. I am well above the rebuild threshold, but 2 cylinders are below the minimum of 128. Is this a concern?

[koolaid_kid]

Your numbers are fine.

[1_v8_merc]

What's the battery voltage, with the bike running?

[glenwill]

Thanks koolaid_kid, and everyone else who replied.

1_v8_merc, I did the quick test on the charging system a few days ago. At idle, it's 12.58, and at 2500 it's 13.7. This is after cleaning a bunch of connectors and wires.

Glen