Kz1100 LTD, 1983, ignition

Starts and runs ok, needs about 1/2 choke to keep running, but it’s fairly smooth. Hesitates when trying to accelerate, but with a little nursing will get to full rpm’s. I checked exhaust tube temperatures at the head, #1 is way low, 140, while the rest are at 240ish. My question is, can a coil, since 1 coil is used for 2 cylinders, could it be not firing to 1 cylinder. I have limited time to spend on it and have not checked caps or plug wires yet, trying to save a minute here and there. Thank you for any input!

Based on your description, my first suspect would be clogged pilot curcuits in the carburetors.

Have you tested compression? You can swap plug and wire from 4 to 1 to see if problem jumps. Only do one part at a time. Has the bike been running recently and did it run good then. Have you checked for obstruction in the #1 carb. Mouse nest perhaps

I think you need to go to square 1 and begin a detailed analysis of your engine. If you don't have a service manual get one asap. When did this bike last run and was it running good? Pull all the plugs and see what they look like, but I would just replace them and be done with it. With new plugs you can really see what the spark is like to each cylinder. As Mikaw stated check your air supply and make sure they are clear. Realistically a compression check should be in order here and certainly a valve adjustment. In fact everything relies on a proper valve adjustment. I am not sure if your bike has one, but check the ignition advancer and make sure it is free. If it isn't it can drive you nuts. Many times in a situation like yours there is not just one smoking gun.
Rick H.

Sloberchops wrote: Starts and runs ok, needs about 1/2 choke to keep running, but it’s fairly smooth. Hesitates when trying to accelerate, but with a little nursing will get to full rpm’s. I checked exhaust tube temperatures at the head, #1 is way low, 140, while the rest are at 240ish. My question is, can a coil, since 1 coil is used for 2 cylinders, could it be not firing to 1 cylinder. I have limited time to spend on it and have not checked caps or plug wires yet, trying to save a minute here and there. Thank you for any input!

It is not so much the coil fires on both; it is more like it needs to spark on both to complete the circuit. One cylinder plug makes positive center electrode, the other one makes negative center electrode.

.... the current flows in the secondary of the coil(high voltage) from one cylinder sparking from block to electrode, to the other one sparking from electrode to block completing the circuit, thus if you open one, the other one would not spark as circuit is not completed...

..........if one fires, it is a good indication the other one is too, and you have different problem as stated in the other opinions given above.

hugo wrote:
It is not so much the coil fires on both; it is more like it needs to spark on both to complete the circuit. One cylinder plug makes positive center electrode, the other one makes negative center electrode.

.... the current flows in the secondary of the coil(high voltage) from one cylinder sparking from block to electrode, to the other one sparking from electrode to block completing the circuit, thus if you open one, the other one would not spark as circuit is not completed...

This is a completely different function then I ever expected. I always thought the plug threaded body was ground to the block. How can that change polarity?

The metal block of the engine is ground, but the secondary does not see it as ground, or actually does not care that it is ground. It's just a conductor to complete a path.

Just as Hugo described, on a coil, one plug wire is positive and the other plug wire is negative. Current flows from one to the other. It just uses the block as a conductor to complete the path. No spark current actually flows to ground.

You don't even need the block to have spark. You can just jump the spark from one coil wire to the other. The coil does not need to be mounted to the bike at all. It is fully isolated from ground. The spark plugs just happen to be in the block because that's where they need to be physically (not electrically). If the block was plastic, the ignition would still work if you just connected the plug bodies together with a piece of wire.

Some other types of ignitions do need to have a path to actual ground.

This page describes some of the more common arrangements for coils and plugs etc.
s3.amazonaws.com/gpzweb/Ignition/Ignitio...esAndCoilWiring.html

I will swap plug wires to day and see what happens, thanks for your help

Will check the advancer to day. I live in a small town with one parts store, went to get new plugs, they only had 2. Will hopefully have a little time to get back to it today. Bike last ran about a year ago, and per owner, not running great. Checked air box, all looks good there. Obviously for the miles on it, the bike has done a lot of sitting. It was kept inside and started every few months. He also said he had rebuilt carbs a while back, how long ago ?. Put a good dose of Seafoam in for now, he had kept it out of fuel until he was going to start it, then just a splash to get it running

Hopefully the previous owner drained the carbs after running it. There are pros and cons of starting a stored machine every so often. I lean towards not. If you don’t get the engine up to operation temp and sustain it for a good length of time you can actually do more bad then good. One being the condensation build up in the crankcase and possible corrosion. I’m more the the camp of putting them in storage with fresh oil change. Drain all fuel from the lines and carb bowls. Adding a fuel stabilizer to the tank. Removing the plugs and adding a very small amount of fresh motor oil and gently turning the engine over a few times, then replacing the plugs. Removing the battery and placing it on a trickle charge in an environmentally controlled area.

I’m not saying this to fault our poster sloberchops, but to make a new member aware of options.

One other thing on buying NGK plugs, here is a perfious post an fake off brand plugs.
kzrider.com/forum/2-engine/612210-fake-n...diums-on-ebay#818095

Keep plugging away and asking questions.

Just one other thing on what the previous owner says, there is a phrase I like to use. Trust but verify!