Oil foul spark plugs

Hello, my kz750 twin keeps oil fouling, idk whats wrong. Please help.

What heat range are the sparkplugs? Are you using B8ES or B9ES?

Mine did this and I ended up rebuilding the whole engine because nothing simple worked. Tried going to a hotter plug and still kept fouling them out. Sometimes a motor just needs the rebuild.

Im using the b8es.

Did the engine rebuild work?

'how long since the valve stem seals were replaced? If they are original, they almost certainly need replacing.

kledda970 wrote: Hello, my kz750 twin keeps oil fouling, idk whats wrong. Please help.

If it is oil fouling, it's almost certainly bad valve guide seals. After you turn off the engine, the oil runs down and hits the plug. Guess how I learned that.... :ohmy:

kledda970 wrote: Im using the b8es.

The 750 twins use the B6ES which is hotter than the B8ES.

Hoyt Clagwell wrote: 'how long since the valve stem seals were replaced? If they are original, they almost certainly need replacing.

+1 I have had my 750 twin since new in 1979, and my seals fail about every 10 - 12 years. Each time I pull the head, I see the oil gunk trail through the valve seats and on the valves from the oil that baked on. You can also see it in the spark plug pocket.

yeah the rebuild worked. I guess it was probably bad rings in my case. Oil should never make it to a plug. If its oil soaked then in my opinion its probably the rings and its allowing the oil to escape. Luckily for me I had a back up bike and didn't lose any riding during the season. I rebuilt the motor then it was winter so I went bonkers and striped it down and turned it into my cafe. Anyone can do it with just a few tools. I think the olny thing besides the rebuild kit that I had to buy was a cylinder bore\polisher that hooks to my cordless drill to get some fine scratches out. If yours is badly gouged you'll have to take it to a shop. I suggest you buy a manual if you don't have one, any take plenty of pictures while taking it apart to reference when going back together. Masking tape and a sharpie helped me a lot.

Hi! I also have the plug fouling issue. The bike runs great with new plugs but they get fouled quite quick. Maybe like 100km or something near that.

Have tried almost everything except oil seals and piston rings now. Really like the bike and I think it will be with me for the rest of my life.
- Dyna S ignition spot on.
- Dynatek coil
- Strong spark with new plugs.
- Valve clearance within specs.
- Former perfectly clean BS38.
- Now new VM34s.

Have not done compression- or leak test yet.

Is it hard to change the oil seals and piston rings? I have the shop manual and read it for a couple of years now:) Do you need the special tools or can you do it otherwise?

//Fredrik

What bike, miles, etc. Common issue with 30+ year old bikes.
Start a new thread on it with lots of pics.:woohoo:
Steve