TOPIC:

I have a 78 KZ650 with the stock Mikuni carbs.
Running pods and a 4-1. Stock jets 97.5. Assuming stock pilot jets.
Air screws are 3/4 to 1 turn out.
I knew I'd be running lean, I did a short drive with new plugs and here are the plug pictures.
Cyl 1 on the left, 4 on the right.
I think it's weird that 1 and 3 seem rich and 2 and 4 are lean.


Will bigger jets fix this? Or do I have a weak coil also?

Thanks,
Dan

With pods you must go up a size or two on the main and fit air corrector jets.
www.kzrider.com/forum/23-for-sale/611992...lide-mikunis?start=0
Base rings are mostly clean and this is your mix strength which is on the lean side .
They should have a full turn of light soot.
The rich appearance on 1-3 may be due to leaking choke plungers.
Plug readings only indicate the fueling at the time of shut off so that is the state of running at idle unless you did a plug chop under load at higher rpm.

I’d check the spark or compression on #2. It doesn’t appear to be firing... either it’s so lean it can’t fire...

I killed the bike under load and coasted to my driveway for the plug reading.
Exhaust of cylinder 2 was hot. It is running.
I will recheck compression. When I purchased the bike last fall, I checked compression, and they were consistent. I don't remember the # though.
I have the air corrector jets, they will be installed when i pull the carbs to rejet.

Is there a way to check choke plungers?

Zed1015 would know, but I’d say if you can just slightly lift the choke lever without and rpm change then you might have a plunger leaking.... adversely if you do start to raise the choke lever and no change then they should be good...

Edit.... I just noticed a mistake....

Adversely if you raise the choke lever and you do get an rpm change then the seat might be good...
Sorry

The choke plungers will be leaking, they all are at 40 years old but it is to what extent.
The sooting may be due to other issues such as oil burning, leaky guide seals or worn ring etc and the overly lean plugs may be due to leaking intake boots on top of increased air from fitting the pods.
The plungers are obsolete and currently i am the only person world wide who offers a Viton re-seating service.
I've just done one set and the user reported that the gas mileage went from 29 to 42 mpg just from that.
There's no real way to test them apart from what Mikaw suggests but even that method may not be conclusive if other problems exist.
I would fit the air correctors and larger mains before you go any further and see how you go from there.

I found some 110 jets sitting around.
should i try those? or are they way too big?

110 to 112.5 are a good place to start.

Thanks zed. I'll start there.

I installed the air corrector jets and wow, seems like a different bike off the line.
I installed 110 main jets, but haven't done a plug chop yet.

At midrange RPM the bike sputters and power drops off.
I think i need to raise the needles correct?
I'm 90% sure i have the needles in position 3. Should i drop 1 step at a time or go all the way to position 5?

I'm pretty sure the 650 stock position is 4 so you need to lift it a notch to get it to stock which may also cure the hesitation.
Feathering the choke at the point of the stutter is a quick way to see if you are lean or rich.
If the the choke cures the hesitation you are lean and vice versa.

Good point on the choke. I will check that out.