Topic: The Mosquito! (Kawasaki KZ250)

[Scott S]

 I'm just getting started on this one, but here's the plan...
 
 After getting a FREE KZ250, I found a titled frame and decided to build a stripped down, bare bones cafe' bike. Old school, 250cc Thumper. Clip on's or low Clubman bars, minimal wiring and lights, drum brakes, skinny tires, etc.
 The old girl only has 19hp, but at less than 300 lbs from the factory, I figure I can strip this thing down to closer to 250lbs.

 I did some research and found out that it's a 1980. I've got to pull the head and free up the piston, but the '78-79 KZ1000's share pistons with this bike and overbores are available.
  Looking inside the clutch side, everything looks really nice and the bike only has a little over 4,000 miles on it.

 Here's the ugly "before" pic:


 And here's a little inspiration. I "believe" it's a Wards/Riverside or Benelli from the late '50's to early '60's. I snapped theses pics in the swap meet at Barber this year.

[Scott S]

 Here's the vicious powerplant. One fourth of the mighty KZ1000!
 I've also determined that the carb isn't stock. It's a Mikuni round bore; no vacuum diaphragm. I haven't figured out what size it is or what it's from, but the P.O. had electrical tape wrapped around the throat to make it fit the manifold. Yeah, I'll have to do something about that.
 But the velocity stack must add 2HP!

[Scott S]

Now, just use your imagination....


 Or maybe something like this?

[Tugboat]

Man, that one in the last picture is totally bada$$! Good luck with yr project!

[Scott S]

 I think the last one is actually a KZ250 twin, but you get the idea.
 I wonder how I can tell what carb I have? There are no numbers on it. If I measure the throat and/or slide diameter, think I can find out?

[Scott S]

 Disassembly has begun. Got the engine out of the frame and lots of unnecessary stuff unbolted. Slapped on some Super Bike bars I had laying around....looks better already, huh?


 I took the engine over to my Dads house. He has LOTS more experience with engines than I do when it comes to getting inside of them. This thing hardly weighs anything!

[Scott S]

 Tied up the cam chain and had the head off in no time. The tach drive pinion gave us the most trouble. It didn't slip out like it was supposed to. Stupid me damaged the seal on the end, but I think I can repair it with an o-ring. We had to remove the cam and then remove the tach drive once we had the head off.

[Scott S]

 This was the source of all our woes. Someone left the bike sitting outside and the piston was stuck. A few raps with a block of wood and a hammer and she freed right up.


 It's a shame, too, because this engine is like new. The piston barely shows any wear, measures out fine and we can reuse it. Unfortunately, the cylinder wall has a ring from the rust that a hone won't remove. No worries, I have a new (used) cylinder on the way.

[Scott S]

 Inside the engine shows like new, as it should with only ~4,000 miles on it. We also peaked inside the oil fill hole and the clutch basket looks the same....like new.
 The oil was fine when we drained it; no water, so I feel like the bottom end is fine. It turns over easily.


 I'm going to try removing the carbon from the head and cleaning up the combustion chamber with a brass brush. Think I can get away without lapping the valves? The rockers, springs and adjusters are all in great shape.

[tbpmusic]

... Think I can get away without lapping the valves? .........

Do they leak??
Sit the head on it's side or whatever - fill the intake port with acetone - watch around the valve face in the combustion "dome" area.
No leakage or seeping is permissible, none at all.

Then turn the head and do it on the exhaust port too.
If they don't leak at all, I wouldn't touch them.

[seanbarney41]

Hey man, I just saw this on KZR...hi there

[Scott S]

 Well, the exhaust valve passes the test, but I'm getting a little weepage on the intake valve. Not pouring through, but over time the combustion chamber did get damp to the touch.
 Not surprising. That's the valve that was stuck open and, I believe, how the water got in the cylinder.
 Think a good valve lapping would take care of it?

[BruceDeuce]

Subscribed!

[kirkn]

Yep, lapping will do it.  Especially if it's just getting damp after a few minutes - not pouring out immediately.  Nice little project.

Kirk

[Scott S]

 The head has been bead blasted, cleaned, valves lapped and new valve stem guides installed.

[Scott S]

 The "before" pictures came out blurry, but here are some "during" and "after" pics of the carb. It was pretty nasty.
  I talked to Sudco and, best they can tell, it's an OEM carb. What model and for what bike...who knows? It's based on/closely related to a VM28. I also found a proper air filter that fits it and a manifold that will only take a little bolt-hole modification to make it work (NOT wrapping with duct tape!    )

[Scott S]

 While I was working on that, my Dad was cleaning the piston, the rings, ring grooves and checking everything to make sure it was within spec. This engine still measures out brand new. It sucks that someone let it sit outside for so long.

[Scott S]

 My girl and I went to a nearby motorcycle junkyard yesterday to scout for parts. We didn't have much luck but ,just as we were getting in the car to leave, she spotted this tank covered in some leaves.
 It's a Garelli moped tank. The inside is pretty clean, it's solid and amazingly straight. It will take some minor frame mods to make it fit, but it's just the look I was wanting. Plus, it was only $15! They had a cool Monza style flip cap for it for another ten bucks!
  I'm not sure of the capacity, but if the KZ250 gets 70MPG, it ougt be good for at least 100 miles. Stay tuned for this one....it's gonna look neat.

[Scott S]

 We got the replacement cylinder all cleaned up and started putting the engine back together.

[Scott S]

The hardest part was getting the cam timing right. It took us a couple of tries, but we eventually got it.

[Scott S]

Not knowing exactly what the carb came from, I had to order a manifold to fit the carb. The mounting holes weren't quite the right spacing, but my Dad took care of that for me.
 Mounts up real nice now. I still have a little cleaning and detail work to do on the lower half of the engine.

[hoodellyhoo]

looking good! Thanks for the updates.

[Scott S]

 Unfortunately, I don't think the tank will work. Even with minor mods to the frame and tank, I can't get the back to fit. I can get the front end down and make it look nice, but because if the backbone on the bike, the rear is going to leave a HUGE gap. It will show the tunnel no matter what I do, making seat fitment an issue. Bummer.

 I do have a "Plan B", though. Stay tuned.

[Scott S]

 So....I picked up another tank to work with. It's not all the way forward on the frame in this pic (yet more customizing to be done), but it looks like it will work.
 Any guesses as to what it's from?


 Maybe this shot will give you a hint. It still has that "skinny" look we were going for.

[Scott S]

And my Dad fabbed up this acrylic plate for the timing cover. Apparently, there's a special "tool" from Kawasaki that's used to time the engine. I guess there's oil behind this cover when the engine is running.
 That "special tool" is a piece of clear plastic, so we made our own.