The Mosquito! (KZ250)

scott s

Over 1,000 Posts
DTT BOTM WINNER
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:
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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.
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Re: The Mosquito!

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!
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Re: The Mosquito!

Now, just use your imagination....
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Or maybe something like this?
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Re: The Mosquito!

Ambitious project. Be sure to post lots of pics so we can see the transformation.
 
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+1! This could be very cool. Im sure those HP numbers can be upped a good bit with some work.
 
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cool little scoot. Might have to do some work with the dip of the seat pan to get inline like the examples you've posted.

It's cool when the small displacement bikes use the big boys pistons. My yamaha sr250 uses the xs650 pistons and rings. Way cheaper by 20 bucks a piston using the xs650.

Jay
 
Re: The Mosquito!

Jeepers Creepers ;D What a score!
The engine must be barely run in.
Good on ya!
:)
 
Re: The Mosquito!

Just a few random thoughts.

Taking that modified one as a starting point, use a squarer seat to work with the engine castings and tank profile which are less round and more square. Maybe an A1R seat might work there.

Please use a small inner rear fender to keep water and rocks out of the carbs. It also make the back end more tidy IMHO.

How about making it into a small version of Eddie Lawson's Z1000 racer or the ELR. That would be cool. Eddie ran #21 so at 1/4 the size, this one would be "5 1/4". That would cause people to stop and ask WTH.
 
Re: The Mosquito!

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?
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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!
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Re: The Mosquito!

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.
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Re: The Mosquito!

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.
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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.
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Re: The Mosquito!

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.
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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.
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Re: The Mosquito!

You probably could get away without lapping the valves but for the little time and effort now is the time to do it.

Keep the pics coming.
 
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The head has been bead blasted, cleaned, valves lapped and new valve stem guides installed.
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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! ::) )
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Re: The Mosquito!

Looks good, glad to see you went with the valve lap. It could make a difference and now it's one less thing to worry about
 
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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.
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Re: The Mosquito!

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.
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Re: The Mosquito!

I like the shape of the tank. Are you going to try to get it to set flatter?
 
Re: The Mosquito!

treitz said:
I like the shape of the tank. Are you going to try to get it to set flatter?

Yes, there are some stubs on the frame that are holding it up right now. Like I said, it'll take a few frame mods, but I'm sure we can make it work.
 
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