Common Problems Among the Z1/KZ Line

Hello,

I am new to the Z1 / KZ platform as well as riding as a whole. I’m building up a 1976 Kawasaki KZ900 from box parts that I was given as well as a good condition frame and decent engine.

Are there any inherent problems with the  platform or anything I need to “bulletproof “ before I put the thing together? I’m not going for a cafe racer build or a stock restoration but more something along the lines of a resto mod. Any advice would be helpful.

The engines are already bullet proof.  The only weakness I can think of is the single disc front brake.  It doesn't. have a lot of stopping power, so you might want to consider duel disc brakes on the front, along with a larger brake master cylinder.

The stock suspension was pretty average when new, and there have been significant improvements since then. You did not mention a specific model, but since you did mention the Z1, I assume you are asking about the liter bikes (900, 1000, 1100). The Z1 and early 1000s had rather wobbly frames. The J-engined bikes (1982 and newer) were a bit better. The police bikes had the stiffest ones. If you are not planning a serious performance build, this will not likely be a problem. 
The biggest problem is previous owners.

wrote:

Hello,

I am new to the Z1 / KZ platform as well as riding as a whole. I’m building up a 1976 Kawasaki KZ900 from box parts that I was given as well as a good condition frame and decent engine.

Are there any inherent problems with the  platform or anything I need to “bulletproof “ before I put the thing together? I’m not going for a cafe racer build or a stock restoration but more something along the lines of a resto mod. Any advice would be helpful.

The KZ "big four" engines are very reliable.  My '78 KZ1000 has about 45k miles on it and it runs great.  Do you have any idea how many miles are on the engine you have?

As mentioned, the brakes are not great.  If you're doing a restomod I would definitely switch to a modern caliper and master cylinder.

The OE steering head bearings use bicycle style 1/4" balls, and over time they dent the race and create a sticky spot on center.  This can make low speed handling pretty sketchy.  Many folks switch to roller bearings, but I just used new factory parts. 

I'm not sure if the rear swingarm pivot on the '76 uses needle bearings or bushings.  But the later KZ1000 switched to four needle bearings.  If you stick with the stock swingarm I'd look into new needle bearings.

For suspension, a new set of quality rear shocks would probably be a good idea.  If you want to get fancy, you can replace the fork damper rods with aftermarket valves.   racetech.com/page/title/GVWHYGV

Or if you're doing a more serious restomod, most people just swap out the entire from end for a modern one.

There are plenty of performance parts available for these engines if you really want to get into it.   kzzone.com/

 

wrote:

The biggest problem is previous owners.

Amen to that!

Mike

The OEM separate regulator & rectifier are disliked by some.  We use the OEM regulators and rectifiers on all of our Z1's without problems and because we have spares on the shelf.  Having said that, the superiority of modern reg/rec combined units is very clear.  The separate OEM regulators used on Z1 and KZ900's are battery maintainers at best.  If tasked with recharging a dead battery while riding, an old-style separate OEM regulator can fail fgrom overheating.  If you use the OEM charging system, keep the battery fully charged.  A good thread on modifying a Z1/KZ900 charging system is here:
www.kzrider.com/forum/forum-index/4-elec...stator-and-regulator

The 20A glass tube fuses are prone to overheating at the end caps.  A good mod is to replace them with modern blade fuses.

Clean all pin connectors & apply something like NO-OX-ID/A.  Corrosion on connectors can cause a variety of mysterious issues.  No-OX-ID/A is available from many sources.includig Amazon and fleaBay:
www.sanchem.com/electrical-contact-lubricant.html www.sanchem.com/electrical-contact-lubricant.html

Most early Z-bikes run power to the coil primaries through a convoluted circuit that includes the ignition switch and kill switch.  The ignition switch, especially, tends to develop resistance across the internal contacts causing voltage drop at the coil primary.  Reduced primary voltage results in weak spark.  An easy mod that will eliminate the ignition and kill switches from the coil circuit is to install a simple relay to apply full battery voltage to the coil primaries.  This can be accomplished with some 18ga. wire to build a PnP harness, a few bullet terminals, a crimper for the terminals, and an inexpensive automotive relay commonly available from auto parts stores.  No butchering of the stock wiring harness necessary; it's all plug-n-play.  The circuit mod schematic is shown below:
wgcarbs.com/index.php/14-sample-data-articles/89-coils

Lube the rear brake pedal pivot.

The grommet in the dyno cover where the three wires exit is prone to weep oil.  Not a leak really, just an aggravating weep.  Take pains to clean/degrease the area squeaky clean & don't be shy with the sealant.  We use high temp silicone.  Others have their preferences.

Old OEM rear brake shoes for the drum brakes on Z1's/KZ900's had the linings attached to the shoe backing with adhesive.  After 40+ years, the adhesive is known to be failing.  If the lining detaches from the shoe while Ridin', it will likely cause the rear wheel to lock.  If that happens in traffic things can get ugly quick.  Replace old OEM shoes with new (not NOS) shoes.

Not platform specific:
Invest is good JIS screwdrivers and impact driver bits.  The cross-head fasteners on Z-bikes look like Philips head but they're not; the geometry is different.  Phillips screwdrivers will damage the recesses of Japanese JIS fasteners.  Vessel is a very good, trusted brand of JIS screwdrivers.  You'll thank your past self in the future for investing in JIS drivers now.

Good ft./lb. and in./lb. torque wrenches will be your friend, as will a factory service manual.

Welcome to our little corner of motorcycle madness  Be forewarned; Z-bikes are an affliction, wherein the first one develops the symbiotic relationship.  It needs you and, you'll find you need it..  The only known treatment is the application of additional Z-bikes.

Good Ridin'
slmjim & Z1BEBE

Very detailed and sage advice in the post above thats for sure. I would add to check valve guides and valve stems and stem seals. The earlier Z1s had bronze guides which although great for heat transfer wore out fast, not sure when they switched over to metallic ones but my Z1a still has them. 
 

Bronze is the only way to go. KHI used steel guides in the later big fours and had to replace them due to excessive oil usage.
Steve

I'm not sure when it was introduced but the Air Switch Valve and assorted plumbing can cause hard-to-find issues. Ask me how I know...

By slmjim+Z1BEBE:  ... Old OEM rear brake shoes for the drum brakes on Z1's/KZ900's had the linings attached to the shoe backing with adhesive.  After 40+ years, the adhesive is known to be failing.  If the lining detaches from the shoe while Ridin', it will likely cause the rear wheel to lock.  If that happens in traffic things can get ugly quick.  Replace old OEM shoes with new (not NOS) shoes. ....

This happened to me when rolling the motorcycle off the center stand in the driveway, so it does happen. Very lucky.  I would hate for it to happen at speed. and far from home to make matters worse.  My old/original brake shoes looked new, so you can't tell by their appearance or go by how much lining wear there is >> the issue is age, not wear.  I installed new Vesrah brake shoes.   
ps: this isn't really a KZ specific problem. any make of brake shoes will fail the same over time.

If any 900/1000 motor is continuity power-shifted under full throttle load there is a 99% chance 2nd OP, and 5th OP gears have rounded off shift dogs on the gears. Causing the motor to drop out of 2nd gear under load. If the bike is ridden with damaged 2nd and 5th gears it will gaul or even bend that shifting fork and damage the shifting drum!!! Very common problem. I have sold hundreds and hundreds of these trans parts over the years when I was a parts manager in large Chicagoland Kawasaki dealerships!!!

If the motor was subjected to a life of drag race style holeshots I have seen a number of the leftside output shaft bearings shatter!!!! If you don't powershift or do a bunch of holeshots the 900/1000 transmissions are damn near bulletproof!!!!

 

Forgot to mention in our post above the issue with enrichener (choke) plungers not sealing when seated, resulting in mysterious rich mixture symptoms.

We're not familiar enough with KZ900 or later carbs, so this comment only relates to the VM28's used on '73 Z1's through '75 Z1-B's. There may be other carbs affected.

The synthetic rubber sealing grommets at the bottom of the enrichener plungers are known to be deteriorating due to age and exposure ethanol.  The resulting poor seal allows unwanted  fuel to enter the intake air stream through the enrichening circuit when the plungers are in the closed position, richening the mixture in unpredicted ways, sometimes causing needless jet replacement and float level tweaking, none of which will solve the problem. 

The plunger grommets can be replaced.

  There's at least one member here on KZR that offers grommet replacement service.  There may be others.  So as to not show favoritism, we encourage our fellow members who offer this service to chime in, and also to offer advice on what other carbs can exhibit the issue & their enrichener plungers be repaired.

Good Ridin'
slmjim & Z1BEBE