cold cylinder (again)

[billbmsn]

A while back my neighbor and I fought with a cold cylinder on his '75. What I mean is, when we checked the exhaust temps on the header pipes on his poorly-running bike, we found 1 cylinder essentially cold. This header would show 200F while the other 3 headers would get to 400-500F rather quickly. We rebuilt the carbs several times, tried them on my bike to verify the problem and finally resolved it only with replacement of the "cold" carb.

Well, now my '76 is displaying the same symptom. The bike runs as if on 3 cylinders except that pulling any of the plug leads still has an effect on the idle and running. One odd things is that as I was riding it around one day, the problem suddenly disappeared and the bike ran great for a few weeks. After the bike sat for a few more weeks, it's back to running weakly.

Cylinder 1's header is 1/2 the temp of the other 3 headers. It's odd that pulling the plug cable to cylinder 1 still causes the bike to die. I took the carbs off, went through carb 1, not finding anything specific, checked all float levels, buttoned it back up and the problem persists.

I suppose not many people check exhaust temps with an IR gun so there not much experience with diagnosing that.

I must be missing something. I suppose it could be something like a sticking choke plate on cylinder 1, couldn't it? That might account for why pulling the plug lead still has some effect.

Any other ideas??

[roncar]

....The bike runs as if on 3 cylinders except that pulling any of the plug leads still has an effect on the idle and running.....

Cylinder 1's header is 1/2 the temp of the other 3 headers. It's odd that pulling the plug cable to cylinder 1 still causes the bike to die.

I must be missing something. I suppose it could be something like a sticking choke plate on cylinder 1, couldn't it? That might account for why pulling the plug lead still has some effect.

Any other ideas??

I can't answer your main problem, but can address the pulling plug dilemma. That is the wasted spark design of the goldwing coils. In order to have a complete circuit the spark voltage comes out of the coil to the #1 plug, thru the head to the #2 plug and back to the coil. Sounds confusing but hopefully this diagram can help you visualize it.



Therefore if you pull the #1 plug wire, the #2 plug doesn't have a path back to the coil so it won't fire either.

[Whiskerfish]

With the wasted spark design of the Wing pulling one plug wire kills 2 cylinders so naturally it would die. Also this is not a good thing to do for the coils as the energy will find its easiest path to ground and sometimes that will create a weak spot in the coil that will eventually lead to failure.

I routinely use a water spray bttle on the headers when troubleshooting a weak cylinder. Not quite as fancy but just as effective as a IR Reader.
One cooler jug is the same basic thing as any running problem. If the spark there is good then it is either compression or fuel. The way you describe the problem reappearing after sitting naturally makes that carb very suspect. I would start there.

[billbmsn]

Thanks for explaining away my spark plug wire pulling anomaly! So, that's not as helpful for diagnostics as it usually is.

I pulled the carbs again (this is getting monotonous), and opened the plenum so I could check the seals and choke plates. All was normal. I will go through carb one more thoroughly, but I'm not sure what would affect idle and open throttle. There was fuel in the bowl when I took the carbs off, and is was the same amount in all carb bowls.

I hope I don't end up like we did with my neighbor - replacing carbs.

[Cookie]

Bill, if you wanted to test I have an extra set of 76 carbs I will probably rebuild at some point. We could rebuild one of those and swap it in.

[billbmsn]

Cookie:

That's a generous offer. I think between my neighbor and I, we have enough carbs. If not, I will let you know.

Hey, we should get together for a ride. My neighbor and I are planning a run this Sunday, maybe over to Alice's, etc. We've been wondering if there are enough SF Bay Area NGW owners for some regular rides.

Well, back out to the garage for reassembly. Hope it's not in vain.

[Briang]

With all due respect, there is no relationship between electrical spark energy going down one spark plug lead to the head and then returning to the coil back up another spark plug lead.

Pulling any one spark plug lead off any one spark plug affects that spark plug only and no other. The diagram offered is misleading as to the internal connections in the coil.

The "wasted" spark is simply the product of the motorcycle manufacturers way around the need for a distributor, such as the ones on conventional automobile engine.

[billbmsn]

DOH!!

FOULED PLUG!!

I must have a leaky valve seal or something fouling the plug periodically. I was so convinced it was the carb, I neglected to pull the plugs. Number 1 was fouled/wet. Cleaned it up and swapped for number 3 and the bike is its old self again.

[billbmsn]

With all due respect, there is no relationship between electrical spark energy going down one spark plug lead to the head and then returning to the coil back up another spark plug lead.

Pulling any one spark plug lead off any one spark plug affects that spark plug only and no other. The diagram offered is misleading as to the internal connections in the coil.

The "wasted" spark is simply the product of the motorcycle manufacturers way around the need for a distributor, such as the ones on conventional automobile engine.

If this is true, then it's a bit harder to explain my observation. Plug 1 tuned out to be wet/fouled, yet pulling the lead to 1 led to the bike dying.

[Cookie]

Nah,

I think it would still kill both but we'll see what others think. This Saturday and Sunday I'm tied up but I'd love to run to Alice's a bit later.
Alice's is fun just for the bike and car show on a good day.

[dan filipi]

Bill, I had a over rich float height causing a cold cylinder, running too rich causing a cool burn.
Took me 4 times pulling the rack to find it.
Turned out being a aftermarket float valve was letting too much gas in the bowl even at the right float adjustment. Finally got it right by measuring the amount of gas then tweaking the float tab to match the other 3 floats.
Better would have been to get a oem valve I know but that would have been too easy lol.

[mooseheadm5]

The current cannot travel from the coil through the head and back to the coil through the other plug wire. Once it hits ground, that is it! This is from experience working on lots of waste spark systems. You pull one wire, you lose one cylinder. Otherwise, you foul one plug, you lose 2 cylinders.

[Frenchy]

With all due respect, there is no relationship between electrical spark energy going down one spark plug lead to the head and then returning to the coil back up another spark plug lead.

Pulling any one spark plug lead off any one spark plug affects that spark plug only and no other. The diagram offered is misleading as to the internal connections in the coil.

The "wasted" spark is simply the product of the motorcycle manufacturers way around the need for a distributor, such as the ones on conventional automobile engine.

Briang is dead on on! The schematic is misleading!!

[Briang]

Thank you, Frenchy.

The coil itself is grounded. When you un-bolt it you can see the metal contact surface molded into the bolt hole. The other end of the circuit, connected to the plug wires, are simply split into two, one for each cylinder. When the high voltage spark current is produced by the action of the cdi ignition components, this current travels to each of the two spark plugs simultaneously and leaps across the gap from the centre electrode to the tang which is grounded to the head. Since all grounds are common the circuit is then complete. It is impossible for current to be grounded back through a spark plug.

[Cookie]

So if you pulled one the other would still fire? Now that I think of it my Chang uses waste spark and I seem to remember getting home on one bad spark lead.