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Group K Modifications for the Kawasaki Ultra 150

Note: The Ultra 150 was released to the public in late spring 1999. With a release so late, most aftermarket manufacturers have not had time to tool up to make the normal array of bolt-on parts. This document outlines the most functional modifications "to date". As more parts are become available for the 150, we intend to test them and update this document with that data.

About the Stock Machine - Since the initial press releases, it was presumed that the 150 would be the fastest production pwc available. At the ’99 Dream Demo (a collective test of new models done by Watercraft World Magazine) the "pre-production" 150 consistently ran 67-68 mph on glass water. However the true production 150s seem to be running 65-66 mph. These speeds still qualify the 150 as the fastest production pwc.

Like any high performance vehicle, the peak performance (and speeds) of the Ultra are dependent on a number of technical features built into the boat … and the good working condition of those features. Of equal importance is the emissions features of the 150 that need to be taken into account. Achieving the 150’s combination of high performance and reduced emissions is the result of very careful tuning on the part of the Kawasaki engineers. Given this, the 150 has a lot less tolerance for "radical" modifications than other pwcs have had in the past. There is no single modification that nets a "huge" increase in overall power on the 150. More than any other machine we have worked with, the 150 responses best to the collective effect of several conservative modifications. In the following text, we will outline the modifications that we have found to net the best overall effect.

The handling of the 150 is very good on smooth water conditions. However in rough water, the high-speed stability requires the skills of a strong and experienced rider. Since high-speed rough-water operation is not the forte (nor design intent) of the 150, the information noted here will speak more to performance issues in water conditions of 1 foot or less.

About Peak Speeds and Radar Testing - (please note that all data related to radar testing assumes very smooth water conditions). Getting the best peak speeds from a stock (or modified) 150 requires some attention to detail. Most high performance pwcs will reach their absolute peak speed within about 10 seconds. The 150 certainly gets close to peak in 10 seconds, however not all the way. The last 1 or 2 mph (as measured on a radar gun) happen as the hull "settles down" at very high speeds. This is fine for the grudge racer who has a good length of water to allow for a climb to full peak speed. However it makes for an added variable during radar tests. In virtually every radar pass we made with our 150 test-boat, the speed was still escalating slowly as the boat "drove off the end" of the radar beam. Taking a long running start into the beginning of the radar beam didn’t seem to make much difference. All this makes it very hard to make valid comparisons during the testing of a machine, and even more difficulty comparing radar data gathered by others. It bears noting that this progressive speed increase takes place only on glass water conditions. If the water surface has 2" wind ripple, those last mph at the far end will not appear. This accounts for why other "radar slower" machines, whose hull-speeds are less affected by "non-glass" conditions, can often hold with the 150 on rippled water … but not on glass.

In addition to this variable, the radar speeds of the 150 are noticeably affected by rider position. The best speeds are attained with no seat contact, and the rider’s feet as far back on the foot pads as possible. "NO" 150 rider will net maximum peak speeds in the normal forward seated position.

About RPM Acceleration - While the overall acceleration of the stock 150 is good, there is plenty of room for improvement. Anyone who attaches an accurate digital tachometer to a 150 will quickly see the reason for the 150’s relatively slow progression up to peak speed. Initial full throttle makes for a "flash" up to an rpm that is about 200 from peak. From that point on, the rpms escalate very slowly (for a mile or more) until the true rpm peak is eventually reached. During the course of our acceleration testing, we had two basic goals. The first goal was to get the engine to "flash" up to an rpm number that is much closer to the peak rpm. The second goal was to reduce the time required to "crawl" from the "flash" rpm to the peak rpm (we call it "crawl-time"). In a perfect world, an engine should flash up to it’s peak rpm and let the improving hook-up of the pump create acceleration. However given the weight of the 150, and the good low speed hook-up of the 150 pump, that is not going to be a reality for any pump gas 150 package.

About Group K Testing - Besides the commonplace radar evaluation, we used a collective of other instrumentation to evaluate our 150 modifications. A Pet 2100 digital tach was used to monitor rpms at all times, and a fuel flow meter was used to show "real time" fuel consumption rates at all throttle openings and rpms. But most important of all, is the detonation-sensor microprocessor (we call it the "Deto") which is capable of showing the rate and intensity of detonation "strikes" for each individual cylinder. These deto sensors are not commonly used by many shops because they don’t "like" getting wet, and they cost about $6000 (we try not to get ours wet). Since the 150 is designed to be such an emissions conscious machine, Kawasaki engineers have built the 150 to operate very close to the detonation threshold (at all rpms) without ever crossing into it. As modifications are tested, the Deto allows us to assess any increase in the detonation risk (we saw this many times). The Deto also allows us to see when a particular modification induces an extreme detonation risk on one particular cylinder (there was lots of that too). With this information we can stagger compression, jetting, and cooling to accommodate these detonation risks, and thereby keep all three cylinders operating at the same temperature. During the course of this document we will make references to observed readings from our tach, fuel flow meter, and Deto.

About the Pump - In most of our previous literature for other machines, we commonly stated peak rpm numbers for stock and modified versions of each machine. For the 150, the job of stating accurate rpm numbers, or relative rpm-to-mph numbers is much more complex because of the 150’s pump design. Kawasaki engineers chose to use the "mixed flow" design pump on the 150 because of it’s exceptional hook-up and acceleration abilities. More importantly, the mixed flow pump can deliver exceptional thrush pressure at relatively low operating rpms. The noticeable peak rpm variations we have observed among stock 150s is a function of the clearance between the tapered impeller diameter, and it’s tapered housing. Kawasaki does a good job of setting the clearance of these pumps within a certain range at the production line. However a small variation in impeller/housing clearance can make for a very noticeable change in peak rpm. Furthermore, Kawasaki takes care to not set up the clearance of these pumps "too close" … which can happen on a stock boat. If the impeller/housing clearance on a stock 150 is too close, the pump will load the engine much harder and cause a loss of peak rpm and a weakening of acceleration (acting like a steeper impeller).

As our test 150 began to produce more power, we shimmed our impeller/housing as close as possible. The result was a 100 rpm loss, but an increase in hook-up and peak speed. Given this, we consider it impossible to accurately connect rpms with speeds unless the impeller/housing clearance is known.

Unfortunately, "shimming" the prop is not an altogether easy process because all the pump components are not "perfectly" centered or concentric. To perform perfect impeller shimming, some of the pump components must be machined, and then hand fitted. This "pump shimming" is a service that Group K will perform to work in concert with modified 150s.

The only down side to the mixed-flow pump design is that it does not deliver big increases in thrust pressure as rpms are increased beyond the "efficiency window". No one knows exactly where the (rpm) efficiency window of the 150 pump is, but our tests seem to indicate that rpms in excess of 7100 seem to offer questionable water-speed benefits. This means that after shimming, blueprinting and re-pitching of the prop are the next most sensible alternatives for increasing the speeds of a high output 150. (Note that the Kawasaki race team uses a stainless steel "axial-flow" Skat Trak pump on their high revving race team machines. These pumps are not cheap, and currently … not available.)

Compression - Like most pwcs, increased compression seems to be the easiest way to increase overall performance. All our initial testing was intended to find the maximum safe compression for the 150 while running on 92 octane pump gas. The 150 responds very well to an increase in compression, within limits. During our compression testing, we quickly learned that all three cylinders experienced very different levels of temperature increase, and therefore different levels of detonation risk. To stave off detonation, and accommodate these different combustion chamber temperatures, the compression ratios are slightly staggered. In addition, the water outlet fittings are also modified in a staggered fashion to further help the temperature equalizing. After all our testing, we would consider any setup using equal compression and equal water flow for all three heads to have a very high detonation risk.

The end result of the Group K compression/cooling upgrade modification is a significant increase in acceleration and peak rpm. The acceleration was increased enough to start causing some prop cavitation at low speeds. With that, we performed the pump shimming modification

With respect to compression, it has been very popular for individuals to use indicated compression gauge numbers for comparison. On the 150, these compression numbers make for a very poor comparison because the vacuum operated slides in the stock CV carbs remain closed during the test process (normal tests are done with the butterflies wide open). For this reason, we do not give much credibility to indicated measurements from 150s.

Flame Arrestors - Like increased compression, aftermarket flame arrestors are a favorite bolt-on performance part. In the case of a pump gas compatible 150 using the stock CV carbs, a flame arrestor is not a good idea. This is not a function of the flame arrestors being poorly designed, but more a case of the carb design not accommodating the change. The stock CV carbs have a conventional throttle butterfly just like all other pwcs. However the CV carbs also have a vacuum operated slide that is driven by the inlet tract vacuum. A freer breathing aftermarket arrestor allows air to enter the carbs more easily, thus reducing the vacuum that lifts the slides. This means that at most throttle positions, the vacuum slide (and it’s fuel metering needle) are considerably lower in the carb bore than they should be. The result is some very serious lean conditions in the mid range (particularly at 6200 rpm). No carb jetting to date has been able to attend to these lean conditions.

We also tested the removal of the rubber air inlet tubes from the stock flame arrestor cover. The net result was a slight leaning out throughout the entire range that offered a "slight" performance increase. However there were occasional detonation strikes at full throttle and at 6200 (note: choke plate removal has a similar effect). For normal use, we recommend that all 150 owners, using the stock CV carbs, retain the "entire" stock flame arrestor.

We suspect, however, that the removal of these rubber air inlet tubes would be a perfect "jetting" tactic for owners who would be operating their 150 at altitudes above 3000 feet.

Carburetion - While the stock CV carbs are not particularly popular among high performance "purists", we have to admit that they work pretty darn good. They start well, meter seamlessly, and offer good performance without ever "loading up". The biggest problem with the stock CV carbs is the poor CFM ability. Besides the uncommonly thick throttle butterfly, the CV throats are also obstructed by the choke butterfly, and the vacuum operated slide … it’s a very busy venturi. The less than optimum CFM ability caused by these obstructions contributes to the somewhat slow "crawl time" up to peak rpms.

Converting a 150 to aftermarket carbs is not an inexpensive proposition, but it is a modification that can pay big dividends in acceleration and peak speed ability. We are certain that carbs of all sizes will be marketed for the 150. However the opening at the reed stuffer is the area equivalent of a 44mm bore. For this reason we chose to test with the 44mm Novi modified Mikuni. This carb has CFM abilities that rival most 46s, and it has stronger "signal" than any other carb in that CFM range. (For more background, see our website document "Racing Carbs 1999"). We first fabricated thin adapter plates that allowed us to bolt the 44 Novis onto the stock inlet manifold. Shortly thereafter, we obtained an R&D "side-draft" style inlet manifold (with matching) reed stuffers. The shorter length of the R&D manifold offered a noticeable improvement in overall acceleration and a greatly shortened "crawl-time". In addition, the R&D arrangement actuated the carbs by a pull wheel mounted between the #1 and #2 carbs (a very tidy setup that is not so hard on throttle shafts). We also used an R&D Pro-Lock type flame arrestor made to fit the Novi carb adapters.

Once the final tuning was completed, the Novis pulled 55 liters/hour, vs the stock carbs at 52 l/h. The increase in acceleration was huge, and the increase in peak rpm was about 60 rpm (on a shimmed pump). We would note that while this carb arrangement starts easily and idles well, it will require "cleaning out" after long no-wake zone riding. The slight rich condition responsible for this is a function of carb mounting location, not metering. Hence it cannot be entirely adjusted out.

Cylinder Porting - The cylinders of the 150 are all aluminum with a Nicasil hard plated bore (as opposed to the traditional steel "bore-able" sleeves of other models). This thin plating is used instead of an iron sleeve because it has a much lower friction coefficient, and it offers a much quicker path for heat exchange to the water-jacket. While the plated bores of the 150 are not bore-able, the hard Nicasil plating is incredibly resilient to the normally damaging forces of piston scoring.

Doing cylinder porting on Nicasil plated cylinders requires particularly good cutting tools along with plenty of special care. We suspect that complete cylinder porting will be needed for 150s that will be used for express racing applications. However for high performance recreational riding, complete cylinder porting may not be the best option. As of this writing, the availability of cylinders (and testing time) has compelled us to defer our 150 cylinder porting tests until autumn 1999.

During our 150 testing, we were able to net a noticeable improvement in high rpm acceleration rate by slightly advancing the port timing with cylinder deck adjustment. That is, we alter the port timing by relocating the cylinder deck position, instead of altering the port windows themselves. This affordable (92 octane safe) deck adjustment modification does not net the huge gains normally seen with traditional cylinder porting. However it does help to address the "slow crawl" to peak rpm that we struggled so long to improve. In addition, there is no loss of low speed acceleration with this mod.

We would note that this deck adjustment has a bigger impact on high rpm acceleration when the 44mm Novis are used (as opposed to the gains seen while using stock carbs). Please note that this cylinder deck adjustment modification requires heads that are cut to different specifications than the head mod that we perform for completely stock top ends.

About High Octane Setups - With both the stock ported cylinders and the deck adjusted cylinders, we setup the maximum safe compression ratios that will support 92 octane pump gas. However we also researched higher compression ratios that required 100+ octane fuels. With these high compression ratios, acceleration (to peak rpm) was increased greatly, and the peak rpm increased by about 50 rpm. We would strongly recommend pump shimming to all 150 owners opting for a "100+" octane arrangement. For 100+ sets that use deck adjusted cylinders, we would also recommend impeller re-pitching (to a steeper pitch).

Ignition - The stock 150 ignition makes plenty of energy, and has a rev limiter at 8000 rpm (well out of the way). A popular modification on past Kawasaki triples has been to bypass the engine compartment heat sensor. When this is done, there is a slight advancing of ignition timing. While this mod may be beneficial for some 1100 models, we felt it offered little performance benefit (and a greatly increased detonation risk) for the 150. We recommend against "any" modifications to the 150’s heat sensor.

There has been much discussion of the unique (and expensive) spark plugs used in the 150. The technical feature that makes these plugs so unique is their exceptional resilience against porcelain damage from potential detonation. We recommend against the use of standard (BR8ES) type spark plugs in stock 150s. We furthermore consider the use of the stock R6918C-9 spark plugs to be absolutely mandatory for any modified 150.

Exhaust System - By spring 2000, there will be aftermarket triple pipes available for the 150. Since prototypes of those systems do not exist as of this writing, we will not address those in this document. The stock "single" pipe on the 150 is a design known as a "dry pipe". That is, the manifold and pipe body are completely water jacketed parts with no cooling water being injected into the interior of the pipe. The only water injected into the exhaust system interior is admitted at the pipe "stinger" end just before the exhaust gases enter the muffler box. Water being admitted at this location helps to reduce sound levels, and cool the rubber exit hoses. Dramatically reducing the water injected into the waterbox has been a popular modification of other models in the past. However the Kawasaki engineers have designed the 150 system to operate with a "close to minimum" amount of internal water. Bypassing a small amount can be beneficial, but bypassing a lot of water can result in burned up exhaust hoses. The additional water being bypassed by our cooling upgrade (done with each head modification) is what we consider the safe limit of reduced water injection into the exhaust. With this cooling system setup, the 150 can be run at peak rpm indefinitely with no risk of overheating any exhaust hoses.

Handling Issues - As previously noted, the stock 150 handles well enough in water conditions of one foot or less. However 150 owners intending to run at speed in rougher water conditions (like closed course racing) will need to make some modifications to improve the handling safety margin at speed. As of this writing, there are no aftermarket ride plates or scoop grates for the 150. We will be updating this document to offer data on functional replacements as they become available.

With respect to sponsons, there are very effective replacements available. The best performing sponson setup we tested was the Beach House. While Beach House has a few versions to choose from, we had the best results with the short faceplate mounted rear-set to the highest position, on a pair of black (angle) back plates. This setup made for a big improvement in tracking and holding high speed turns. We would consider this to be a mandatory modification for any 150 owner planning to race closed-course or endurance. The only down side to these sponsons is that they cause a "smooth-water" peak speed loss of about 2mph. This is of little consequence to closed course racers, however it’s an importance concern for smooth water "grudge racers".

It bears noting that the Kawasaki factory-team uses the more aggressively angled "white" back plates. Apparently those machines have other handling hardware that makes for safe use of those back plates. It "would not" be a good idea to use these white back-plates on a stock hull, even for closed course racing.

Comfort & Control - While the high speed rough-water handling characteristics cannot be improved profoundly (for now), it is possible to enhance the rider’s ability to control the 150. The first, and easiest means of improving control is by installing an aftermarket mat set that allows for better foot traction. It bears noting that there is a great need for improved foot traction against the outside of the gunwales as well (this is the area where your foot often sits during high-speed turns). The Hydro-Turf brand mats we chose for our test machine worked great for the bottom surface, and we found an effective solution for the side surfaces.

Before removing the stock rubber mats from our 150, we thoroughly cleaned the painted surfaces along the entire length of the foot gunwales. We found that the stock mats on our 150 peeled away from the hull very easily. While the stock mats were being peeled off, we noticed that the adhesive on them was still very sticky. Since the inside and top surfaces of our gunwales were already perfectly cleaned, we immediately laid each stock mat panel outward to cover the top and inside of the gunwale in that area. This made for excellent full length traction on all sides of both gunwales.

Another big improvement in control came by adding a 2" tall pad to the seat. The added height of this pad makes the 150 much more comfortable for taller riders, and makes it easier to hold on to the seat with your legs. This +2" seat modification is also done by Hydro-Turf. Hydro-Turf sells a taller seat cover with the pad, or you can have them do the installation of seat cover and pad for an additional charge. Installing the pad correctly is a bit tricky, so we recommend having Hydro-Turf do the installation (we had them do ours, and it came out "clean").


STAGE 1 MODIFICATIONS -- 67-68 mph (92 Octane)

Cylinder Head/Cooling system Modification (Standard Cylinder Spec)                 190.00

Pump Shimming                                                                                                  95.00

STAGE 2 MODIFICATIONS -- 69-70 mph (specify 92 or 100+Octane)

Cylinder Head/Cooling system Modification (Deck Adjustment Spec)                  190.00

Cylinder Deck Adjustment Modification                                                          260.00

44mm Novi Mega-Flow Carbs (with linkage, and throttle bracket)                          1114.00

44 Carb Fit Kit - (includes primer kit, R&D Manifold, R&D stuffers, R&D Arrestor)    522.90

PET 2100DX Digital Tachometer                                                                              308.00

Pump Shimming                                                                                                      95.00

"Impros" Impeller Blueprinting and Re-pitch                                                               78.00

Hydro Turf Mats                                                                                                      69.00

Hydro-Turf Seat Cover & Handlebar Pad (+2" Seat Mod - 60.00 additional)             79.00

Beach House Sponson (short faceplate w/black back plate)                                     170.00

*prices subject to change based on manufactures pricing


GROUP K 4597 CALLE DEL MEDIA FORT MOHAVE, AZ. 86426 928-763-7600

GETTING THE WORK DONE - Most customers send GROUP K the parts needed for modification via UPS, and then do the engine assembly work themselves. We also do complete engine and pump assemblies for customers who want a finished unit ready for installation. The new 150-lb. UPS weight limit makes engine shipping practical and affordable.

All orders prepaid with a cashiers check or money order will be returned freight free via ups ground service anywhere in the continental United States. All other orders will be billed to a visa/master card or sent freight collect cod cashiers check (ups no long accepts cash for cods). If you would like to pay additional for 3 day, 2 day, or 1 day return shipment, please specify your preference in a cover letter with your parts. Be sure to include your return address and day phone information in case we have any questions regarding your order.

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