1982 550 LTD #2 cylinder issue

I am trying to troubleshoot my #2 cylinder not firing. Heres the story:

Holed piston 1 year ago because running lean. Lean condition is believe to be fixed (cracked carb manifold boot thing). New piston, rings, valve job, valves adjusted, carbs are clean. Compression is 130 lbs and climbing as things wear in and seat.

So, this #2 cylinder was firing when I first put things back together, but #4 had a clogged pilot circuit. I got that sorted out, and now #2 won't fire. It won't fire at idle or open throttle. I figure since it won't fire at open throttle it's not a plugged carb passage. I can get it to sputter if I close the air/fuel mixture screw (really rich mixture). Swapped spark plugs, no change. After about 5 minutes, the cylinder starts to fire and things are good.... So, since it used to fire, I'm thinking its a electrical issue...maybe I could use some new plug wires or have a loose connection from taking the coils on and off a few times? Does it make sense that after the bike warms up a weak spark would be sufficient to fire the cylinder, but cold it isnt?

There is (as usual), many different reasons for a cylinder not firing.
So... you need compression. Which you have apparently in abundance, so lets scratch that out.
Spark. OK, so you can swap the coil connections and wires and see if the problem moves to another cylinder.
If it does, its a spark/electrical issue, there ya go.
If not...
Air/fuel ratio per "gulp".
So... when you pull the plug, is it sopping wet/flooding? Not from the sounds of it. Therefore, more than likely an air leak. Its gulping in air from some external source.
So... start spraying some wd40 around the carb holder and intake/airbox end of the carbs. Dont forget all the possible entry points, like the vac tubes (a crack maybe), linkage, etc.
Make sure the mixture screw o-ring is there. Dont forget to check the gaskets...

GL!

Hopefully this will speed things along for ya...

Thanks for the reply. I was pretty sure everything was sealed up tight, but now I am questioning whether I remembered to put the vacuum cap back on the #2 carb intake holder....

The plug wasn't dripping wet, but it was wet and smelt like gas, so I figured it was getting gas.

I was in a hurry last time and was only able to swap plugs, so next time I work on it (The bike is at my parents place because working on it at my dad's shop is much easier than my garage) I will tinker with the cables since that should only take 5 min. Then back to taking the carbs off again! It's not a big deal... I'm getting pretty good at it!

So I had a couple minutes to tinker with this issue yesterday. I verfified that the problem cylinder had spark. Not the most impressive spark, but it should have been sufficient. I tightened all connections down and fired the bike up. It ran better than last time and actually wasn't missing on #2. However, the header for #2 is hot, but not scalding hot like the other 3 pipes...any ideas?

With ignition switch ON, what is voltage measured at ignition coil primary terminal? (Red/yellow wire.)

Good Fortune!

Not sure. It was close to 12 V after I did the WG coil mod. That was 2 years ago though. I'll have to check it when I get a chance.

What ignition is fitted (oem igniter; Dyna-S; other)?

And what spark plug wires (original; Dyna wire core; other)?

Even with adequate voltage at coil primaries, something is causing poor spark quality. Perhaps a coil is failing; or plug wires are leaking; or weak connection somewhere between coil output and spark plug tip); or plug cap failing or leaking; or simply a bad plug; etc.

Good Fortune!

OEM igniter, newer but non-dyna wire core wires.

I will use my multimeter and do the tests on the coils and see if theres a problem. If its not the cap/wire/plug for #2, and in fact the coil, wouldn't I be seeing an issue on #3 also?

apbling wrote:

OEM igniter, newer but non-dyna wire core wires.

I will use my multimeter and do the tests on the coils and see if theres a problem. If its not the cap/wire/plug for #2, and in fact the coil, wouldn't I be seeing an issue on #3 also?

Imo, given perfect wiring, caps and plugs on both #2 and #3, the spark quality on #2 and #3 should be equal, as both are in the same secondary loop relying on output from the same coil.

Having a strong spark on #3 plug (which indicates good coil performance) and a weak spark on #2 plug would seem to indicate an issue with cap/wire/plug for #2.

If not already done, would remove #2/3 plugs and directly compare visually observed spark quality, and then repeat the observation with two brand new plugs.

What plug caps are fitted? And have the caps been ohm checked?

I prefer Dyna solid metal core plug wires that come pre-fitted with non-resistant caps, and used on non-resistant plugs. In other words, zero resistance between coil and plug spark, but which, if it matters, will result in radio interference. If resistance is desired, it should be in only one place, either in the wire or the cap or the plug.

A simple high intensity leakage test is to spray water mist over the plug wires in a dark garage with the engine running, and watch for sparks.

As known, with good spark quality on all plugs, plus correct ignition timing, and a properly functioning advancer, combustion failure could point to poor compression (perhaps a too tight valve clearance), or imperfect air/fuel mixture (carbs or carb related).

Good Fortune!

I figured this issue out!!! I had some time this weekend, so I opened the carbs again to clean them. I still had to have the idle screw on #2 turned further in than the others. I went for a ride and noticed that it would miss as I neared wide open throttle. I checked the fuel service level...and sure enough, #2 was really low for some reason. So, I have since adjusted all 4 carbs to within spec and it idles like a dream! It has power off the line and as long as you don't go wide open throttle, things are great.

However, if you go wide open, it misses badly. I think it's not related to RPM's, its thottle slide position. I think this because I went up a hill with it and my RPM's dropped, so I opened the throttle and it started to miss. It's very easily reproducable.

I have yet to synch the carbs. When de-accelerating there is lots of "chatter" from the pipes. Not backfiring, but popping chatter. I did have the carbs broken apart from one another to clean them and I notice there is a screw to limit the amount the throttle can be open. When I open the throttle, it does not hit this screw, so one of the slides must be hitting the top of the carb. I did bench synch them before putting them on the bike.

Is it possible that the throttle is being opened too far and starving the motor of fuel?

apbling wrote:

I figured this issue out!!! I had some time this weekend, so I opened the carbs again to clean them. I still had to have the idle screw on #2 turned further in than the others. I went for a ride and noticed that it would miss as I neared wide open throttle. I checked the fuel service level...and sure enough, #2 was really low for some reason. So, I have since adjusted all 4 carbs to within spec and it idles like a dream! It has power off the line and as long as you don't go wide open throttle, things are great.

However, if you go wide open, it misses badly. I think it's not related to RPM's, its thottle slide position. I think this because I went up a hill with it and my RPM's dropped, so I opened the throttle and it started to miss. It's very easily reproducable.

I have yet to synch the carbs. When de-accelerating there is lots of "chatter" from the pipes. Not backfiring, but popping chatter. I did have the carbs broken apart from one another to clean them and I notice there is a screw to limit the amount the throttle can be open. When I open the throttle, it does not hit this screw, so one of the slides must be hitting the top of the carb. I did bench synch them before putting them on the bike.

Is it possible that the throttle is being opened too far and starving the motor of fuel?

Is it possible that the throttle is being opened too far and starving the motor of fuel? NOPE.

And imo pilot circuits and sync aren't related to performance issues at WOT.

Would look to ignition (health fat blue properly timed spark) and compression (including valve clearances to spec).

Might possibly be a main jet issue, dirty or loose or wrong size.

Or maybe dirty or obstructed air filter.

Or maybe enrichment (choke) circuit remaining partially engaged when supposed to be completely off.

Good Fortune!

If not already done, would assure correct functioning of ignition timing advancer seeing it quickly move back and forth under a timing light as rpm is varied by blipping the throttle.

Advancer may need lubing, or both cleaning and lubing.

Good Fortune!