Compression significantly different between throttle open and closed…why?

wrote:

Yeah that’s how it’s set up.

update: I’ve got 13.3V at the battery. Voltage at the ignition coil leads are both 11.7. Is that normal? That doesn’t explain why one cylinder isn’t firing but I thought they should be at or near battery voltage

edit: if both ignition coils are unplugged from their leads, they will read the correct voltage. I don’t understand why it would make a difference

Should be no more than 0.5v different to battery voltage,
ref your edit - resistance faults show when the circuit is under load with current flowing. When you disconnect the coils and measure voltage in a dead circuit you get false readings.
If the rest of your electrics are working ok then the below link might be helpful
Ignition by-pass relay W - KZRider Forum - KZRider, KZ, Z1 & Z Motorcycle Enthusiast's Forum

So with one coil disconnected I get battery voltages.

With both connected I get a 1.6V drop.

Could you point me in the direction you’d go on this to sort it out?

Both coils and the plugs and wires are all only a few month old. Condensers are only a few months old. 

 

wrote:

So with one coil disconnected I get battery voltages.

With both connected I get a 1.6V drop.

Could you point me in the direction you’d go on this to sort it out?

Both coils and the plugs and wires are all only a few month old. Condensers are only a few months old. 


 

The cause of this is in the supply to the coils ( not any of the components you have changed) this is a result of age related corrosion and loss of spring tension in the connectors and switches throughout the circuit. You can follow the resistance fault finding process in my " fault finding guide" (FAQ section) but it is likely you will find lot's of small loses along the way adding up to the total drop you have at the coils. With resistance faults "the longer it is running the higher the resistance will become" this is due to heat build up caused by the resistance. As I said previously if everything else on the "ign" circuit is working ok the by-pass relay mod will save you hours of work eliminating lot's of small resistances along the way. Many members have been running this mod for years without issue to overcome this age related problem.

Do what you have to do. I did the same mod and got a strong spark and the bike starts on the first push of the button.

HELLA 4RA 003 530-001

 

I will definitely look into this. I think it’s worth noting that I got nearly the exact voltage reading at every connection all the way to the coils as I get at the battery itself. There was maybe a .02V drop by the end. Not sure if that makes the mod less useful or not. I’ll read up on it more

wrote:

I will definitely look into this. I think it’s worth noting that I got nearly the exact voltage reading at every connection all the way to the coils as I get at the battery itself. There was maybe a .02V drop by the end. Not sure if that makes the mod less useful or not. I’ll read up on it more

Are you taking the readings with everything connected and the engine in a position where both sets of points are closed (maximum current draw) DONT FORGET TO CHECK THE COIL TEMP AND DON'T LEAVE POWERED FOR TOO LONG  if so what happened to the volt drop you described when both coils were connected ? - if you take voltage readings with the consumer disconnected you will go down a rabbit hole

Ok jump back from a business trip. Checked the coil voltage at each lead on both coils. 

13.30V at the battery
13.30V at each lead 

Just rebuilt the accelerator pump and #2 cylinder got up to operating temps at idle!!! Big breakthrough. The old vacuum sensor diaphragm was rotten. I think this may help.

wrote:

Yeah that’s how it’s set up.

update: I’ve got 13.3V at the battery. Voltage at the ignition coil leads are both 11.7. Is that normal? That doesn’t explain why one cylinder isn’t firing but I thought they should be at or near battery voltage

edit: if both ignition coils are unplugged from their leads, they will read the correct voltage. I don’t understand why it would make a difference

If these readings are with the coils connected then you have a magic touch given the previously reported volt drop   It is possible that you had a corroded connection and, that by unplugging and re-fitting during your testing has scraped it clean enough to make a good connection !