Kawasaki 750 misfiring when hot mystery

[ShreddinSD]

So my current problem is that after about 15 minutes of run time(hard run time) once everything is hot, I have a bad misfire like it’s only running on one cylinder. Someone in a previous thread that I believe had the same problem described it as the sound of slow machine gun fire. There was no resolution in that thread. Only the one post stating the problem actually. This is a mystery to me since this is a lost spark system and it can’t possibly be firing only one cylinder-I don’t think. I have tried swapping multiple things with the same results including spark plugs(which I also tried .020 gap with no change), cut wires back, stator, even swapped in a whole different e box with CDI and coil. The e box has not been tested but performed as it should for 15 minutes until the same problem occurred. I think I have swapped everything and the problem persists. I have been to the bay to test and failed five or six times now so it’s getting old. The last time I did not have my test E box secured well as the wires are short and it pulled a sp boot off the plug. I limped back on one cylinder running just like it does when it gets hot, cut the wire back 1/4” and it ran for a few minutes till it got hot and did the same thing. Once it is hot and misfiring it’s pretty much game over for that day. It needs to cool for a long time before it’ll be back to ripping…for 15 minutes. A long time ago I had a similar problem due to a fuel filter that was getting too restrictive after about half a tank but I have been through my fuel system, have no filter and even got a new sbn46 chasing a recent fuel problem.( My fuel pick up tube was leaking under the fuel cap but only at high rpm AND the seals on the butterfly shaft on my carb were worn.instant runaway.) It definitely feels like ignition to me now. Right now I am suspecting a coil so I will buy a brand new OEM SXR coil. It seems like it could possibly be broken sp wires but I have tested with the second ebox and coil so ?? Sorry for the long read, this is frying my brain!

Thanks for any help, there’s got to be something I’m missing

 

[WFO Speedracer]

Usually on 750's doing that it's a bad stator , that being said Kawasaki spark plug wires are crap , yours are most likely 25 + year old crap , I have seen on several Kawi's over the years seriously broken spark plug wires , on a 650 I worked on in a span of like 12 inches the wires were broken at least in ten places, all of those small breaks are like additional spark plug gaps , I would start with a new coil and work from there.

Also ohm out the spark plug caps to make sure there is no high resistance hiding in there , one more thing IMHO you don't need resistor caps and resistor plugs , one or the other , you are adding resistance the spark has to jump with each resistor component that you add to the system , it's the same as widening the plug gap , a spark will only jump so much gap before it starts to misfire , on an old ignition system with an old coil and 25 year old wires it might just be enough to cause a misfire.

I hope this helps , if the shoe fits wear it , if not throw it back in the closet.j

 

[kevbo]

Pull the plug caps, trim back the insulation, and pull on the center wire. It’s probably okay if the wire won’t pull out. Next look at the stator, they are likely to cause temperature related problems.

 

[Scorn800]

Change the coil with the wires with OEM kawasaki, use the OEM plug boots

 

[ShreddinSD]

I ordered a new oem sxr coil and plan on swapping in yet another used stator. This one’s teal so it might be a couple years younger than the others…wires look good. I think the coil is off a 1994 yami wr3. plug boots ohmed at .005

Could a leaky head gasket possibly have these symptoms? (ADA head new o rings but the deck was not mirror finish) Start to leak once it’s hot? I popped the head off just to see and one exhaust port looks a little milky. Thing is, that’s the mag cyl with 175psi and the pto only has 165 now. I felt at least two times like there was water on the sp after a plug chop but wasn’t sure if it had been from my hands. That was when tuning before it got hot and falls on its face…

 

[ShreddinSD]

I always use the blue oem sp boots. Does it matter with a Zeel CDI if you use resistance sp boots or not? They require resistor plugs is why I ask. I’m waiting until I get things sorted to swap in the Zeel…

 

[WFO Speedracer]

Usually on Kawis it's the deck surface that's uneven if there is a head gasket leak , it is from the studs pulling causing an uneven surface, the only way to tell is pull all the studs and sand it on a surface plate.

 

[ShreddinSD]

it was the stator. Back to brap )

 

[WFO Speedracer]

it was the stator. Back to brap )

It usually is

 

[Myself]

It usually is

You called it! I was thinking the same thing as well.