1978 KZ750B Twin barn find.

Hey folks,

New to the forum here. I picked up a neglected KZ750B. After a little TLC I managed to coax the thing to run for a short time. As this thing needs everything restored, I am thinking about doing a cafe build. Does anyone have any tips or tricks specific to this model and make? Thanks!!

I've got the same bike and once I got it running somewhat properly I absolutely love riding it. It's a wonderfully torque-y, relatively smooth-running engine with decent handling once you do your suspension right.

Since you're going to need to do a full restoration, here's a few things to look out for:

1. starter clutch - notorious for being unreliable and for coming apart, sometimes dangerously while riding. Take it apart, do a rebuild of it with a kit and use blue loctite on new allen head bolts when you put it back together. It's the same unit as off the 400's, so it's not big enough to reliably move the 750 engine. A lot of owners switch to kick only because of it.

2. Points ignition sucks. There's a guy that makes an electronic ignition kit for it which makes starting and running much, much more reliable and smooth. Check out 7thgeardesigns.com. Well worth the money.

3. Valve clearances - The engine uses a shim over bucket design and the shims in a certain range are hard to come by, or at least used to be before the guys at Z1 Enterprises started selling them. Z1's a great resources for old Jap bikes, BTW. I couldn't have done my rebuild without them.

4. Head gasket is prone to leaking. Replacing it is a perfect excuse to do a top end rebuild to make sure all that's in order.

That's all I can think of right now. You really ought to check out some of the websites dedicated to this model, like kz750twins.com, where you can download a factory service manual Do this immediately and spend hours reading it before doing anything. It'll be your bible going forward. There's also the KZ twin owner's forum, although that appears to be down for the moment.

If you need any help/advice, I may be able to help, so feel free to message me and I'll be happy to tell you what I know. Glad to hear another of these rare beasts will be back on the road again!

I am currently doing a KZ750 twin build myself. Everything Aramund said is spot on. It looks like that ignition over at 7th gear designs is actually ignition produced by C5. I recently bought one myself, directly from C5 http://www.c5ignitions.com/motorcycle-ignitions.html

Post some pics ;D

Wow! Thanks guys. I have the starter clutch rebuild kit already as well as the Athena complete engine gasket kit. I will look into the electronic ignition and Z1. The bike has 2002 tabs which means its been sitting for over a decade. :/ I've found a few posts about tuning for air pods. Sounds like carburetor parts are fairly hard to come by, so that should be interesting. I will get some pics posted before too long. This is going to be my winter project as I have too many bikes coming and going from my garage at the moment. Just finished getting a Honda trail70 up and running.

Cheers!!

A few members over at KZRider have had bad luck with the athena base gaskets leaking, or any of the green gaskets for that matter. For that reason I ended up going with a Versah gasket kit myself. I just rebuilt my BS38's and the parts are not too hard to come by; Z1 enterprises sells rebuild kits with everything you will need and JBM industries sells new diaphragms, finding main jets can be a problem if you need to rejet, but if you look around you can find what you're looking for. If you are going to go with pods get K&N or Uni as the cheapo pods will block partially the diapraghm intake. If you have your airbox boots I happen to know a guy that would be interested in them, wink wink, nudge nudge ;D

Actually, let me second advising against any aftermarket gasket sets. I used the Vesra set and every single gasket, except the head gasket, in the set started leaking, some as early as 800 miles after my rebuild. I know it costs more money, but OEM gaskets are the only way to go. You'll have to scour eBay for them, but, trust me, you'll be better off.




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Here we go. First pic is the day I bought the bike. Today I finally put it up on the bench to start the project. Pulling the flywheel off to replace the starter clutch. I still don't have it off. Since I don't have the proper puller, we are using the rear axle as suggested in a few other forums I've been reviewing. Threads right in. I gave is a few whacks with the BFH and it didn't budge. It's under load right now and hopefully I won't have to bust out the hot wrench. We'll see what happens over night. Any suggestions from you savvy folk?

I wasn't able to get the rear axle trick to work either. I pounded on the end with a sledge and the generator didn't budge. In the end I sprung the mere $18 and bought the rotor puller tool, put it on an air impact, then drove that sucker out. You can get the tool from z1enterprises.com.

When you put it back on, make sure to clean the tapered crankshaft end with acetone or alcohol, put blue loctite on the reverse thread bolt, hold the generator/flywheel with a plumber's strap wrench, then torque it down as hard as it will go. The torque spec in the manual is not sufficient and the bolt will come undone. That will leave you stranded (ask me how I know) or, worse, throw you from the bike when it causes the engine to seize.

I wound up fabricating a tool to hold the flywheel by the two holes in the side in order to impact it down as tight as possible.


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Btw, here's what came of all my efforts. I call it the Beesticorn, part wildebeest, part unicorn. I hope this pic posts ok...





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More work has been done on the Kawi. Will post pics soon. I got the flywheel puller via UPS yesterday and 2 seconds with the impact popped it right off. Found one of the starter clutch springs all tweeked. Assembled the contraption with some new starter clutch components and that's done!. I pulled the engine out of the frame and really started looking at what needs to happen for the engine build and chassis mods. One simply complicated question I have is where to find some over sized pistons. I plan on pulling the top end apart and cleaning everything up. Not sure if I will even need larger pistons but just trying to stay ahead of the game. I've found a few o/s pistons on ebay but they are few and far between. I would be buying pistons from separate sellers because everyone only has 1 piston... Once it's apart I'll know what size to get and hopefully I'll be able to match up some part numbers. That is unless you folks know where to find some. Stay tuned, shit's about to get real!

Unfortunately there are no aftermarket pistons for these engines. Your best bet is to stay on ebay and score some NOS. I have been waiting to find a group buy in for some custom pistons for a 830-900 kit. There are some people out there that have done some custom big bore kits but they aint sharing their secrets.

I saw one of the 800 kits on ebay. Not sure what they wanted for it. They said it would fit the KZ, but if I want to go do wheelies I'll just take the Buell out. My plan is to keep it at 750cc if I can. I've put together enough hopped up H-Ds to know that bigger is usually faster but at the cost of longevity and reliability. Sooo the search continues.

The engine is on the bench ready for a freshening. Starting to really look at some styling options.

I'm thinking taller shocks in the rear, and doing the pvc spacer upgrade in the front forks.

Looking at cutting off the rear fender and welding a hoop in. New or modified seat and modified front and rear fenders.

There's so much more to do to this Slow and steady it's moving along.

In relation to using the rear axle to remove the rotor, you need to have part of an M6 bolt inside the crankshaft end to "load up" the axle. Then you tighten the axle down on this bolt and give it a whack.


Worked first time on my old GS450

I'm in for the twin. I did the starter clutch on mine but used an oem replacement rather than the kit. I'm really glad I did, one of the 3 main bolts was loose and had already rattled around a bit. Looking forward to seeing what you do with this one Gunstein.

We have just a little progress. The top end came apart nicely. Got my hands on some measuring equipment and went to town. We are just past our service limits on the cylinder diameter and way over on the piston to cylinder clearance. Looks like we're going to bore it over and get some O.S. pistons. I foresee lots of scraping and cleaning in my future.

Oh yeah here's a few pics.

I bookmarked this site long ago in case I wound up needing pistons in the future:
http://www.cyclewareables.com/pages/vintage_piston_rings_kits/vintage_piston_rings_kits/vintage_piston_rings.htm

Never ordered anything, so don't know much about them, but I suspect you'll need to,call them to make sure they've got the ones you need.

Also, when you reassemble the engine, heed the mantra for gaskets: OEM, OEM, OEM...kinda like the "ommmmmm" you mumble when sitting in the Lotus position, contemplating why you can't get your racing carburetors to run right on a bike they were never intended for.


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Armaund, that is a great resource for us old kztwins. am I reading correctly that you get a piston AND rings for $36? what a bargain!

That is a truly amazing link and you can bet your ass that I'll be giving them a call. Just a little update on the progress. Took the cylinders to the hone tank and cleaned them up. After a re measurement and a second pair of eyes, we determined that we are well within our service wear limits. The pistons are still shot, but new standards will do the trick. Thanks for the link Armaund!!