New coils less power

Hello! Picked up a 79 kz650. Pulled really good but stumbled hard at mid rpms. Got Valvles in spec. Has 4into1 and stock air box with new filter. Put the 17.5, 115 and needle on 4th. Still same. 

Found that one of the coils was going out when hot (dyna coils) replaced with Amazon ones. Stumble is gone but is super under power. Any suggestions? Thanks a million!

Do the replacement coils have the proper resistance?

My leads= .1-.2ohm
old coil (dyna) .1-3.2ohm till hot then 8+ OL
new (Amazon).6-3.8ohm

Could that .6-.8ohm make it waaaay less powerful? Feels like it went from a 1000cc with a mid range stumble to a 250cc that has a slow steady speed increase. If that makes sense. 
The exhaust pipes are all getting hot and they all have vacuum. Carbs are synced up.

I don´t know your bike but the old carb rubber boots are brittle inside and can create an air leak. More air let run the engine very lean and you loss power. Spay some break cleaner around the boots. If the idle goes up or down it´s indicate an air leak. Don´t forget to check your ignition timing is adjusted correct and the advancer is lubed and moving freely to set the correct ignition timing on higher rpm.

wrote:

My leads= .1-.2ohm
old coil (dyna) .1-3.2ohm till hot then 8+ OL
new (Amazon).6-3.8ohm

Could that .6-.8ohm make it waaaay less powerful? Feels like it went from a 1000cc with a mid range stumble to a 250cc that has a slow steady speed increase. If that makes sense. 
The exhaust pipes are all getting hot and they all have vacuum. Carbs are synced up.

What is the supply voltage to the coils with them connected and the engine running ?
Did the coils come with the leads ? (I would normally expect either the leads or caps to be resistive with a reading in the range of 5 - 15 Kohms)

wrote:

I don´t know your bike but the old carb rubber boots are brittle inside and can create an air leak. More air let run the engine very lean and you loss power. Spay some break cleaner around the boots. If the idle goes up or down it´s indicate an air leak. Don´t forget to check your ignition timing is adjusted correct and the advancer is lubed and moving freely to set the correct ignition timing on higher rpm.






no air leaks that I could find. 

 

wrote:

wrote:

My leads= .1-.2ohm
old coil (dyna) .1-3.2ohm till hot then 8+ OL
new (Amazon).6-3.8ohm

Could that .6-.8ohm make it waaaay less powerful? Feels like it went from a 1000cc with a mid range stumble to a 250cc that has a slow steady speed increase. If that makes sense. 
The exhaust pipes are all getting hot and they all have vacuum. Carbs are synced up.

What is the supply voltage to the coils with them connected and the engine running ?
Did the coils come with the leads ? (I would normally expect either the leads or caps to be resistive with a reading in the range of 5 - 15 Kohms)





I'll get that info tomorrow morning. Thank you.

 

wrote:

Hello! Picked up a 79 kz650. Pulled really good but stumbled hard at mid rpms. Got Valvles in spec. Has 4into1 and stock air box with new filter. Put the 17.5, 115 and needle on 4th. Still same. 

Found that one of the coils was going out when hot (dyna coils) replaced with Amazon ones. Stumble is gone but is super under power. Any suggestions? Thanks a million!

First question.  Did you change anything else, other than the coils, between when it "pulled really good' and "super under power"??


Second, you mention you're running 17.5 pilot and 115 mains.  The factory service manual lists a pilot jet of 15 and a main jet of 97.5 or 102.5 depending on the country where it was sold.

Are you running the stock 1979 VM24 carbs?  If you are using the stock carbs with the stock airbox, a main jet of 115 is very large.  Even if you have an aftermarket 4:1, most of the time rejetting isn't necessary if you keep the stock airbox.  

How did you arrive at 17.5 and 115 for jets?

Have you got the HT leads mixed up.

I used the ignition cables and boots from the dyna coil I took off.

#4= .3ohm boot 13kohm
#1= .1ohm boot 5kohm

#2= .1ohm boot 5kohm
#3= .1ohm boot 5kohm

With engine idling at 2k rpm with black lead on negative and red lead on positive post on coil.

Right side coil = OL ohm, 5.9VDC, 9VAC
Left side coil = 1.9-3.9ohm, 0VDC, .08-.1VAC

From everything I have looked up on the internet and my manual they seem to be the stock carbs. It has a accelerator pump that from my knowledge is working. At least with a bench test when pumped vigorously. Haha.

I got the jet sizes from the internet. What sizes would you recommend with this set up? Back to stock?

wrote:

I used the ignition cables and boots from the dyna coil I took off.

#4= .3ohm boot 13kohm
#1= .1ohm boot 5kohm

#2= .1ohm boot 5kohm
#3= .1ohm boot 5kohm

With engine idling at 2k rpm with black lead on negative and red lead on positive post on coil.

Right side coil = OL ohm, 5.9VDC, 9VAC
Left side coil = 1.9-3.9ohm, 0VDC, .08-.1VAC

That's good, so you have resistive caps. With the voltmeter, the black lead should be on "Battery negative terminal" and red lead on coil feed (yellow/red I believe)
PS: you can't measure resistance (ohms) in a live circuit