Any suggestions? KZ750 motor issue

[Ituen]

My bike overheated a little over a week ago. I made an appointment for my bike shop, but I got tired of waiting and decided to pull the plugs. The bike runs, but I don't want to run it or ride it anywhere until a mechanic looks at it. I pulled the sparkplugs and the outside ones look OK. Just a little carbon on them, dry fouling. The inside plugs have oil on them. I also noticed the hoses (clear greenish blue) going to the outside carbs have dark fluid in them. Any ideas to what's wrong? Someone here mentioned the bike was running lean after the carb rebuild with a jet kit and Vance and Hines exhaust. Did I blow a head gasket? Is the motor toast? Any ideas?

[Ituen]

No ideas, guys?

[Alizard]

Oil on plugs can come from a several reasons: collapsed oil ring and leaky valve seal are the most common.

If you blew a head gasket, the bike should be running terrible.

Fisrt thing I would check is cylinder compression.

I can't tell from the picture if it is water cooled, if so check the oil for radiator coolant.

[Ituen]

It's an air cooled motor. I'll buy or borrow a gauge to check the cylinder compression. Thanks!!!

[Partstime]

How did it act when it overheated? Did the oil light come on? Check the spark on the inside cylinders...you may have a bad coil.

[Ituen]

Originally Posted by Partstime

How did it act when it overheated? Did the oil light come on? Check the spark on the inside cylinders...you may have a bad coil.

It started to smoke everywhere. It wouldn't idle or stay running without opening the throttle. I could smell burnt oil. The oil light would come on when it stalled, but the bike would restart easily. I could hear a ticking sound from the top of the motor. It sounds OK now when I first start it up, but then it runs funny and the ticking is back.

[oldcoldankles]

I experienced the exact same symptoms when my wife accidently put diesel in our weedtrimmer.

[Ituen]

I'll test the compression over the 4th of July weekend. Stay tuned!

[agawam]

just in case I have a good 82 650 engine for sale or trade, near springfield

[vinnye]

Compression test is the place to start - and also see if your oil level is dropping much.
Was the smoke mostly out of the exhausts or was it from around the motor itself?
I agree with Bountyhunter - if it was your head gasket the motor would run badly and you should be able to see where it was blowing from. It would leave a trail of carbon etc that you could see.
Not sure about the liquid you mentioned in the hoses?
Have you tried draining the carbs at the bleed off screw at the base?
It could be that you have some crud in your gas?
An in-line fuel filter would be a good idea on such an old bike - you may have rust / debris in the gas tank itself that has collected over the years and has got past the screen on your petrol tap.

[Ituen]

agawam: Thanks, but I'm going to do a motor swap. I want to put something in with more power.

vinnye: The smoking was from the motor. I have a couple of oil leaks (cam gasket and head gasket) and smoke came out from those areas.

[A2rider]

So what motor are you going to put in it?

[Ituen]

I'm thinking about putting a '00-'02 ZX6R motor in it. KZ750s (738cc) with the 810 big bore kit only dyno about 80-85 whp. I'll be in the 90-95 whp range with the factory ZX6R. Hopefully it won't be too difficult to get 100 whp from one.

[A2rider]

You might want to think about frame flex.

[Ituen]

Originally Posted by A2rider

You might want to think about frame flex.

I already have the "frame flex" issue covered. I'm going to use a modified crash cage. The motor is carbed, so I don't have to go through the pain of wiring the bike for fuel injection.

[StarGate]

Originally Posted by Ituen

The motor is carbed, so I don't have to go through the pain of wiring the bike for fuel injection.

Yea but what about the rest of the wiring?

[A2rider]

Originally Posted by StarGate

Yea but what about the rest of the wiring?

I haven't looked it up, but do the speedo and tach still work off cables?

[Ituen]

Yes, I have to change the instrument cluster over.

[gpzrocker]

I just had my 750 motor out and in the parts washer at the shop. Interesting thing is these aircooled 750's are H-U-G-E. I imagine that when the measuring is done, there will be some cool spacers on the motor mounts. Not sure I would want really long bolts holding in 100HP, so I imagine that creative blocks or tabs could be welded on.

End result should be interesting: lighter but what looks and is a physically much smaller motor in a big 80's frame -- in my mind I see a few inches between of the tank and the motor. That and frame rails that completely enclose the motor.

Interesting.

So how did you overheat said motor? I have done some pretty stupid things to KZ motors: When I lived in VA Beach I would spend hours on the strip, moving maybe 40 ft an hour in the blistering heat. I thought I was cool, now I realize I was an idiot, but the bike never died in a way that it wouldn't start up within an hour of rest, and never blew a gasket.

guess I was just lucky with them bikes. That watercooled Yamaha gave me fits though.

[Ituen]

Originally Posted by gpzrocker

"...So how did you overheat said motor?...".

Someone here mentioned the yellow-blueish coloring on the header from my pics was the motor running lean. I guess I didn't fatten it up soon enough. I got stuck in rush hour traffic in a tunnel on a 90-degree day. The bike started idling a little faster and oil smoke started coming from the gasket areas. I heard a little tapping noise from the top of the motor. It wouldn't idle. I had to keep the throttle open so it wouldn't die. It runs fine when it's cold, but I'm not a mechanic. I really didn't think it was too bad until I pulled the plugs and found the oil on them. I just got it back from my motorcycle painter too. The paint is brand new.