FAQ about KZ900 / KZ1000 Engines
Larry Cavanaugh’s website used to have a forum and he had a useful FAQ page. The forum is gone and luckily I saved the FAQ and am reposting it here for the KZ community.
Here's a list of common questions with answers related to KZ900 / 1000 engines. The answers come from a lot of years of experience with these bikes. This information is intended to help people make wise, cost effective decisions. Money comes hard for most people so spending it wisely is always preferable. If you pay attention to the information provided here, you can get the most bang for your buck and have a strong running Kawasaki as the end result.
There are two ways to do things. The RIGHT WAY & THE CHEAP WAY.
How big can I make the motor without larger sleeves?
KZ900 - 1015cc
KZ1000 - 1105cc [1075cc is suggested as the safe size without potential heating issues]
Do I need to weld the crankshaft?
That depends on what you're going to do with the bike. If it's going to see the drag strip regularly, then yes, absolutely. However, the old standby answers held water 30 years ago when the bikes were still relatively new should be taken with a grain of salt. These engines are OLD now. There's only one smart move when considering a performance build . Split the cases and inspect everything in the bottom end. Once the crankshaft is in your hands, for a couple of hundred dollars, you can have it inspected and welded. Then you know it's good.....no guess work. The condition of the connecting rods and main bearings has nothing to do with welding. Welding the pins simply prevents the counter weights from slipping and throwing the crank out of index.
Should I have the head ported?
If you want considerable power gains, absolutely you should have the head ported. What's important in that matter is how you intend to realistically ride the motorcycle and how large you're making the motor. Some shops that like to push selling camshafts because there's no work involved or they don't have anyone who can actually port the head properly will tell you to just buy their cams and have them do a valve job. You're going to get a performance gain from even the mildest drop in cam. But, consider this, when the stock head flows 68CFM @10" of water at .500" lift [a lift only a serious drag bike would ever see] but a properly ported head flows 68CFM at .250" lift, you're going to get a lot more out of the cam's potential than you are with a stock head.
Which cams should I use?
There are literally at least a dozen good grinds that I could suggest for a particular KZ motor. Web, Megacycle, PSP, APE, & Cam Motion all have a grind that will suit a specific application. You can still find some other brands out there but the will be used cams. Norris and Kenny Harmon had some really nice grinds as well. Andrews grinds are now owned by APE except their old 3X which is now ground by Megacycle for PSP. An important part of the cam selection is budget related and ease of maintenance related. The old Shim on Bottom vs Shim on Top debate crops up. Let's address this one because it's really not a difficult situation to figure out. Cams designed to use Shim on Bottom will require you to come up with a few hundred more dollars toward the build. Most times,you don't need them. There are some really nice grinds that work great and allow you to:
a] take advantage of the additional flow from porting
b] make valve adjustments easy
c] give great performance increase
d] save you that extra few hundred dollars you would be spending on new retainers & buckets.
Let's look at it from a common sense approach. You're going to get far more performance gains from spending the additional few hundred dollars on port work with the right cams that allow you to keep Shim On Top valve adjustment than you are out of picking some cam that requires shim on bottom buckets & retainers run with a stock head. Think about it.
Same holds true for applying that extra money toward a good set of carburetors. Shim on bottom setups are a total waste of money on 99% of street motors. Don't waste your money on those items. Not when you can get a great cam that doesn't require it.
The correct cams are the cams that suit your intended use for the bike. The cam effectively shapes the power curve. In combination with a good flowing head & the right carburetors, a 1075 - 1197cc motor will produce a nice broad power band with a cam that provides about .400" lift with about 250 degrees of duration at .050" checking lift.
The more you favor top end power, the more duration you want. The more you favor bottom end and midrange, the less duration you want.
The KZ 900 / 1000 heads stop gaining significant flow above .350" in stock form. The real difference in performance a cam with .400" lift makes to the engine can best be taken advantage of when used in combination with good port work. I've heard some people say that you loose velocity when you port a head for the street. Well, that depends on who's porting the head. Anybody that doesn't look at your entire engine combination and takes the time to discuss your intended use of the bike is probably just a salesman pushing their goods. They just want your money.
A carburetor's job is to feed the engine the maximum amount of air it requires while providing the correct fuel curve. The first part is simple, larger carbs flow more air. Carburetors can be classified into 3 groups. We'll break each group down but first address some common sense
issues.
* OEM Manual Throttle Slide
* OEM Constant Velocity
* After Market Performance
Just as it is with cams, the carburetor scenario has it's little catches. Budgets are the biggest factor when guys set out to build an engine. To make matters worse they get sold down the river by salesman that tell them that bigger is always better. It's got to be. It only cost a couple dollars more to go from about right to huge! Get the most for your money If you have the luxury of being able to select any carburetors you want, you're probably in a situation where you can properly build an engine without cutting corners.
Let's put things in perspective. The old VM series carburetors did their job fairly well, all things considered. Rejetting for POD filters was not difficult either. The latter CV [BS34] carburetors did their job fairly well also, as long as either of 2 conditions were adhered to.
1 Leave the air box on
2 Buy a proper jet kit [POD Filter Use]
The old VM series carbs, Early 28mm, then 26mm then back to even better 28mm with accelerator pumps could all be tuned in relatively quickly. Then in 81 the BS34's showed up on J motors. People got all kinds of confused trying to make them work properly. At best, most were over jetted on the pilot and main circuits and lean in the middle. The reason was because the needles were not correct when the air box was removed. There wasn't enough progressive taper to the needle. Shimming them up didn't get you on the taper quickly enough. Another snag with CV carburetors is what happens when you put cams into the picture. The pulsing and vacuum signals can get those carburetors all kinds of confused. Effectively the slides don't care what kind of signal they receive. They simply react to the signal and open or close. Fine....except the needle is connected to the slide and it's controlling the amount of fuel the engine is receiving. With any carburetor there are 2 basic elements that absolutely must be adhered to or jetting will be a problem.
1 Absolutely Clean
2 Correct Fuel Level
OEM MANUAL THROTTLE SLIDE CARBURETORS [VM Mikuni]
The original Z1 900's came with VM28 Manual Throttle Slide Mikunis. Some people really like those carburetors. Personally, I think they're inferior to the late model VM28's with accelerator pumps. The early 28's had a horrible linkage setup and could be a chore to synchronize accurately. 30 plus years of wear hasn't helped them any. Still, all things considered, not a bad set of carburetors but not the best that ever came down the assembly line. Years do tend to bring improvements and carburetors are no exception.
In 77 Kawasaki downsized the carburetors to 26mm with completely revised throttle linkage. They performed adequately and were a lot nicer to synchronize. However, the 2mm decrease in throat size makes them less than the ultimate OEM carburetor for all out performance. Don't misread that statement though. Those carburetors work just fine on a stock motor.
The 79 MKII saw the return of the 28mm carburetor with the superior throttle linkage [like the 26's] and accelerator pumps to boot. Those, IMO, are the best carburetors fitted to a KZ 1000 from the factory. LEAVE THE FUEL PUMP ADJUSTMENT ALONE. The 1980 LTD also had the late model 28's with accelerator pump.
CONSTANT VELOCITY CARBURETORS [Mikuni BS34]
These carburetors operate the slides based on intake manifold vacuum. The slide has a bellows connected to it with a return spring that sets in a well in the top of the slide. A throttle plate is mounted in front of the slides. The throttle plate is controlled with the twist throttle. The intake manifold vacuum controls the slide lift speed. It's assisted by vacuum bleed holes in the bottom of the slide. Enlarging those holes allows he slide to lift quicker. Also affecting the lift rate is the slide return spring.
Kawasaki engineers are not stupid. They knew the wanted to fit larger carburetors to their redesigned engine [J Model] but they also knew that fitting 34mm manual throttle slide carburetors would probably lead to customers bitching about bogging when the the throttle was quickly opened fully from low RPM. Combine that with meeting emissions standards [both sound and pollution] and you had a pretty tall order to fill.
When they designed the J motor, the cylinder head received a complete remodeling as well. Larger port runners and valves were part of the layout. Putting larger carburetors on the engine was a natural course of events. After all, they were actually slightly decreasing displacement 998cc vs the former 1015cc. Not a lot of difference but still, it was a tad smaller.
Ultimately their solution was the BS34 Mikuni Constant Velocity carburetor.
To me, those particular carburetors don't make a lot of sense on a stock KZ head. They're too large for stock KZ port runner entrance. To get the most out of them on a KZ, the port runners need to be worked. I've seen so many forum posts where guys pull their hair out trying to dial in a rack of BS34's on a KZ engine. Add some cams to the mix the posts go on for ever..... Just a poor choice IMO but one that seems to happen a lot. I suspect it's mostly a matter of budget constraints that leads guys down that path. I can understand that.
AFTER MARKET PERFORMANCE CARBURETORS
We have for the most part 2 carburetor manufacturers that produce after market performance carburetors, Keihin & Mikuni. Both make some really nice carburetors.
In the early days, we had the Keihin CR29's on race bikes and Mikuni VM29's on street bikes. Both were smooth bore types. The CR later became the CRS with much improved idle circuits. Very nice carburetors.
Mikuni introduces the VM33 Smooth Bores around 1980. Completely revised from the VM29 version they provided additional performance but really didn't deliver well at partial throttle openings. They could be sensitive to weather changes and were not near as good a carburetor as the next generation RS series.
Keihin made available a wide variety of throat sizes in it's CRS series. Just how many of the actual sizes you can still get today, I can't say for certain but the most popular were 29, 31 & 33 CRS. The CRS series lacks the sophistication of an accelerator pump and there are times when that would have been nice to have. Mikuni did at one time have a kit available to add the pump to theirs.
The next progression from those two manufacturers was the move to flat slide smooth bore carburetors. The RS Mikuni and FCR Keihin. Both are improvements over the old round slide types. The flat slide arrangement provides very good low speed, part throttle smoothness and the improved throttle response from the accelerator pumps allows for running a carburetor
throat size that would be too large in a round slide type.
CARBURETOR COST FACTORS
This is the part that I've so often seen ignored. Shop around an see how much a rack of BS34's costs to have gone through. Shop for a used rack of VM29 Smooth Bores. Then price a brand new rack of After Market Performance Carburetors. You'll see that for not a whole lot more money, you can get a brand new rack of carburetors vs a uses set. With the VM29's stripped out
jet blocks are a common problem. The're repairable but for the money, it just makes a lot more sense to buy new and start with something fully and easily tunable.
CYLINDER HEADS
Essentially you have 3 OEM cylinder heads to work with.
* KZ 900 / 1000 [68-70 CFM]
* J Model [72-74CFM]
* GPz11 Bathtub Chamber [82-84 CFM]
You can use any of those heads on a KZ motor providing you use the correct pistons and correct the deck height. There are however logical reasons to use a particular head on a particular motor.
On KZ motors up to 1197cc, the KZ head is fine. It can be ported appropriately for that size engine. It's once you go beyond that size that it makes sense to start looking at a J or GPz Bathtub Chamber head.
I've seen a lot of guys top off a big block KZ with a ported KZ head running 36mm Intake Valves. Sure it will work but it leaves a lot to be desired in all out performance. Reason being is the valve size is way too small. In a hemi head you want an intake that's at minimum 51% of the bore diameter. Let's look at some numbers.
Using KZ head with stock valve seats
KZ900 Motor - 66mm Bore, 36mm Intake Valve 36 / 66 = 54.5%
KZ 1000 - 70mm Bore, 36mm Intake Valve 36 / 70 = 51.4%
1075 cc Motor - 72mm Bore
36mm Intake Valve 36 / 82 = 50%
37mm Intake Valve 37 / 72 = 51.3%
38mm Intake Valve 38 / 72 = 52.7%
A KZ head will readily accept a 38mm GPz 1100 Intake Valve 1395 cc Motor [Here you can see the intake valve size is inadequate for a big motor]
82mm Bore
36mm Intake Valve 36 / 72 = 43.9%
37mm Intake Valve 37 / 72 = 45.1%
38mm Intake Valve 38 / 72 = 46.3%
IS THE J HEAD THAT MUCH BETTER THAN A KZ HEAD?
Yes, it's better for certain purposes. The J head can be mounted to the KZ engine with the addition of a top idler assembly and some modifications to increase the compression. The J head has a larger combustion chamber volume that will reduce the compression if KZ pistons are used. It's possible to shave the J head to bring compression back up but that's really not the
best method. The correct way is to use the proper pistons & correct the deck height by adding a spacer under the cylinder block.
From a flow perspective, the J isn't a killer over the KZ, even though it has 1mm larger intake valve and larger port runners. The J head requires porting to bring out it's potential. Remember, those larger runners were meant to have BS34 carburetors feeding it. However, it wasn't until the 1983 GPz11 that Kawasaki finally put a fairly good cylinder head on their engine. It's worth noting that the 84 & 85 LTD 1100 also received the same basic cylinder head as the GPz11 got in 83. The engine temperature sensor isn't drilled out and tapped, it's silver instead of black but the porting and valves are the GPz spec.
HOW DO I FIGURE OUT WHICH HEAD TO RUN?
The decision to run a particular head depends mostly on your overall view of the engine. A couple of immediate thoughts would be:
* It's a shame to deck the heck out of a J head to make it work with KZ pistons.
* The GPz11 Bathtub chamber head has port runners that are too large for a little 1015cc motor for street use.
* You can't really feed a big block motor properly with a KZ head if you intend to race it and get the most from it.
For a street motor up to 1197cc, the KZ head [if you already have one or if you already have KZ pistons] is the right one. You can make a great 1197cc street motor with a KZ head using GPz11 Intake Valves with the correct cams to create a motor that makes great torque, idles well and behaves very well in
stop and go traffic. In fact, it would serve as an excellent touring type motor or a killer / sleeper cruiser motor [LTD].
If you're making the motor big and you can get your hands on a GPz11 Bathtub chamber head, then that's the one to start with for such a project. If not, get a J head. In either case, get the correct pistons and correct the deck height.
MYTH The largest valve you can run on a stock KZ 900/1000 valve seat is a 37.5mm Intake. REALITY A KZ 900 / 1000 head will readily accept 38mm Intake Valves. Use either GPz11 or GS1000 Intake Valves
MYTH You need a billet after market cam chain tensioner. REALITY OEM Cam Chain Tensioners can easily be modified to provide reliable cam chain tension in KZ motors.
MYTH Removing the air box improves performance significantly. REALITY Modifying the stock air box by removing the rear silencer portion and the screens from inside the box is a very effective modification for performance.
MYTH OEM S.O.B. valve buckets are fine to use with performance cams and springs. REALITY You're pushing your luck if you run that setup. Good After Market Buckets should be used in performance applications where performance valve springs are required.
MYTH A .365" lift cam is a waste of time & money. REALITY With a good cylinder head, cams like the Andrews 2x & Web 118 are very nice cams
for motors up to 1075cc.
Larry Cavanaugh specializes in porting and engine building.
http://www.cavanaughracing.com/
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