Kawasaki STXR 1200-Ultra 1350 – Single Pipe Engine Kits

During the development of the triple pipe exhaust systems for the STXR & Ultra, the technicians at Factory Pipe products encountered an unusual problem. All the carefully monitored dyno tests had yielded very steady and consistent performance from the triple pipe setup. However once the similarly tuned engines were operated on the open water, a new problem surfaced. Their on-board fuel flow meters showed that after the first 30-40 seconds of peak rpm running (on glass water), the fuel flow began to slowly, but steadily, decrease. At this same time, the on-board detonation sensors began to show indications of increased detonation. As the peak rpms were sustained longer, the fuel flow continued to decrease, and the detonation activity steadily increased to a point that would clearly cause a piston failure. The fuel systems were inspected thoroughly to try to find the cause of the progressive “leaning out” condition… but no fuel system problems were ever found. After some brainstorming (and many other tuning attempts that had no effect on the problem), the FPP techs decided to block off the crossover passages that are built into the stock inlet manifold. This modification instantly yielded two obvious results. First, the jetting that seemed perfect before, was now very over rich. Secondly, the progressive fuel flow reduction at extended high rpm passes was completely eliminated. The jetting was then leaned out to compensate for the new over richness. Once that was done, the machine could be operated at full throttle for any amount of time with absolutely no drop in fuel flow taking place.

Armed with hindsight, the FPP techs theorized that the crossovers (used by the manufacturer to offer smooth low speed response) were causing a “progressive inlet signal contamination”. It seemed that the lower rpm, and lower inlet signal, of a stock engine were very nominally effected by this “contamination”. However, the triple pipes made the inlet tract signal so much stronger, that the signal could be compromised by the crossovers. There is some disagreement among technicians about how or why this phenomenon takes place, but there is absolutely no disagreement among those who have done the on-water testing that the phenomenon is real, and tied solely to the inlet cross overs.

We had no trouble believing that the improved scavenging of the triple pipes could induce this problem on machines that retained the stock inlet manifold (with crossovers). However we then began to wonder if the inlet signal variations created by our single pipe Stage 2 kits (or 1350 big bore kits) might also be subject to this same phenomenon. Equipping a Stage 2 Ultra with a digital tach, fuel flow meter, and detonation sensor quickly showed us that we experienced a similar version of the same problem. Where a triple pipe Ultra might see reducing fuel flow after 30 seconds, our single pipe Stage 2 Ultra began it’s fuel flow reduction after 90 seconds of full throttle on glass water. As the Stage 2 run got even longer, the fuel flow slowly but steadily reduced to the point where we too experienced detonation. After blocking all the crossovers in the stock inlet manifold, we also experienced the same result as the FPP techs… the carburetion was way too rich. After recalibrating the carbs, we found we could run indefinitely at full throttle with absolutely no loss of fuel flow shown on our gauges … and also no progressively increasing detonation.

We theorize that the change in port timing, and higher target rpms, of the Stage 2 kit work together to bring about this phenomenon. The Stage 1 kit (milled heads) does not appear to impact inlet signal enough to be subject to the same phenomenon (in 4 minute long passes on glass water anyway). It bears noting that a Stage 2 machine that is never held at full throttle on smooth water (for a minute or longer) would never experience this problem. Backing out of the gas for just a few moments seems to “reset” this fuel flow phenomenon created by the crossovers in the manifold. Just the same, we are now making crossover block off a standard part of all future Stage 2 and 1350 big bore kits.

After spending a great deal of time doing carb calibration work on “blocked manifold” engines, we found another characteristic. The individual signal received by each carb is so strong that very minor changes in metering make for significant changes in fuel flow (much more so than with a stock “crossovered” manifold). With this, the gap between CV jet sizes (160-165-170) turned out to be too big to offer ideal jetting. Since Kiehin does not (and will not) offer 162.5s and 167.5s, we now fab our own jets to be used in the Stage 2 kits and 1350 kits where they are effective. Given the precision of metering with the “blocked manifolds” we have found that staggered jetting is often required to offer ideal performance and temperature control.

As is often said…”hindsight is 20/20. This entire process has allowed us to look back at several STXR and Ultra platforms that we have seen operate with total reliability….. then suddenly for no apparent reason fail a piston. We strongly suspect the inlet crossovers were the ultimate culprit in virtually all these situations We realize that there are many owners running engine setups of all variations that might wish to get the carb jetting data for their setup. To that we can only say that the testing for our Stage 2 kits took weeks, and so we will not be attempting to predict what jetting might be needed for the many different setups that owners are running. We will, however, be making available the odd size CV main jets (we will be calling them 155+, 160+, 165+ etc) for those wishing to attempt their own tuning.

About Oil Injection – The Ultra and STXR are equipped with a very unconventional oil injection system. The injector pump has 5 output fittings. Two “half feed” fittings deliver oil to the front and rear balancer bearing reservoirs, two other “half feed” fittings deliver oil to the injector fittings on the #1 and #3 carbs. A check valve in the two balancer reservoirs releases oil into the #1 an #3 crankcases. The half feed from each of those check valves, and the half feed delivering to the #1 and #3 carbs makes the full oil requirement for those cylinders. The fifth fitting from the oil injector pump delivers a full feed of oil to the center carb. Removing the oil injection system requires that the cases be split and the two check valves be replaced by plugs. Then the engine would need to be removed to periodically change the oil in the oil in the balancer reservoirs (a lot of work to say the least). Given this complexity, we opted to retain the oil injection system for all our single pipe kits.

With the strong accent on emissions of pwcs, Kawasaki has set up this injection system to deliver the equivalent of about a 60:1 premix ratio at full throttle. This volume of oil may be acceptable for a recreational machine that doesn’t rev very high and is not held at peak rpms for extended amounts of time. However for any true high performance platform, this is not enough oil… and the stock injector pump cannot be adjusted to deliver more oil. Given all this, we recommend to add a premix of 1 ounce per gallon to all Stage 2 and 1350cc kits (equating to roughly 40:1). For machines that will be used constantly at peak rpms, we recommend 2 ounces per gallon premix (equating to 32:1).

Ignitions – The stock ignition unit on the Ultra and STXR has very effective mapping and a unobtrusive rev limiter (7400 rpm). The only modification we recommend (for 100+ octane versions) is the substitution of the engine compartment heat sensor with a resistor to facilitate a 3 degree ignition advance. This advance allows for improved acceleration and peak rpms.

Ultra 150 Pump and Prop – Except for a few specification variations, the pump modification for all our Ultra single pipe kits is essentially the same. All kits require a Solas DynaFly impeller, exit nozzle taper boring, and pump shimming.

The Solas DynaFly 16/20 impeller offers several advantages over the stock prop. A) The stronger blades of the Solas props are far less likely to be bent or damaged by debris or rocks. B) The blades flex much less than stock, and reduce cavitation. C) The Solas props offer more thrust, per rpm, than the stock impeller. The 16/20 pitch seems to work best overall on all our Ultra kits.

During our testing, we found that taper boring of the pump exit nozzle improved the acceleration and top speed (about .8mph) of every Ultra equipped with a Solas 16/20 prop. We consider this taper boring to be a mandatory modification on all Solas 16/20 equipped Ultras.

The components of the Ultra pump are manufactured in a way that seldom permits the closest possible shimming of the prop. In most cases the impeller housing is slightly oblonged and/or not concentric with the impeller, leaving large clearance gaps. When we shim the Ultra pumps, we machine various parts in an effort to obtain the best possible concentricity and clearance, thus reducing cavitation.

As mentioned in our other Ultra documents, the condition of the pump bearings and seals is very important. A worn or “water invaded” front bearing can allow the prop to come in physical contact with the impeller housing, causing an immediate loss in peak speed. As a general rule, we prefer to replace any Ultra pump bearings and seals that have been in service over 60 hours. We consider it money very well spent.

TECH UPDATE INFO: Over the last years, we have built countless Ultras using the Solas 16/20 prop. During this time, we have seen some variations in performance that we attributed to subtle variations in the boats themselves. Very recently, we constructed two identical 1350 big bore machines for two customers also using the 16/20 Solas. To our surprise, one machine revved to the normal 7100 rpm target, and the other revved to only 6800 rpm. After a week of teardown and inspections of every kind, we were grasping at straws for a solution. Finally we just swapped the pumps on the boats. Instantly, our 6800 rpm boat became a 7100rpm rocket, and the machine that turned 7100rpm now turned 6800. The issue was obviously traced to the two props. We spent a considerable amount of time inspected the two props, and found some subtle blade specification differences that were not apparent by a normal visual comparison. We then altered the “steeper” 16/20 the match the specs of the good one, and recovered our lost 300 rpm. With this experience behind us, we realize that these small variations in specification can have huge impacts on peak rpm numbers … and off-the-shelf 16/20 props seem to vary greatly. We further realize that many of the peak rpm and performance variations we had seen in past modified Ultras may very likely have been due to prop variations… not boat variations.

After specing a number of 16/20s with these same adjustments, the rpm results can vary within a 50 rpm range …. but that’s alot better than a 300 rpm range. As a result, we will be inspecting and setting the spec of every Solas 16/20 purchased from us with any of our kits. We will also offer this service to customers wishing to have their existing 16/20 prop adjusted ($45).

STXR Pump and Prop – Even though the 148mm pump in this model is somewhat smaller than other 1200cc 3 seaters, it can offer great performance when mated with the right prop and nozzle diameter. In the STXR, we have had the best overall results (to date) with the Skat Trak “Swirl” impellers. The Stage 1 STXR utilizes the 14/24 pitch, while the Stage 2 and 1350 kits run the steeper 16/25. Like the Ultra, these props work best when used with a taper bored exit nozzle. As with the Ultra, we have found two diameter variations that seem to give best results. The smaller of the two diameters is offers slightly better peak speeds, while the larger offers much better acceleration with a 1mph loss of speed. Performance minded owners will want both diameters.

Since the STXR pump is an axial flow design, there is no pump shimming required. The clearance between the impeller and housing is fixed, and not adjustable.

Ultra Handling Parts – Handling (especially on Ultras) is a very subjective thing because no two riders preferences are the same. For Ultra owners interested in sheer smooth water speed, the stock scoop grate, ride plate and sponsons are hard to improve on. However some owners wish to improve “rough water” handling. This can be done, however it bears noting that any effective rough water handling parts will take a toll on peak speeds. The most popular arrangement appears to be the Shreadmaster ride plate used in conjunction with the R&D scoop grate and the Beach House Sponsons and Aqua Sports steering nozzle extension. This setup offers a huge improvement in turning ability and rough water stability, while only causing a 2-3 mph loss on smooth conditions…. a worthwhile trade off for anyone operating an Ultra in very rough water conditions. For the very serious Ultra owner, we also strongly recommend the UMI steering system.

STXR Handling Parts – For owners wishing to maintain the maximum smooth water peak speed abilities, the stock hull parts are hard to beat. The R&D ride plate offers an improvement in steering and straight line stability with little effect on peak speeds. The Worx scoop grate seems to offer the a good increase in hook up while scrubbing of only 1-2 mph. The best sponsons seem to be the adjustable Beach House sponsons. These sponsons make for a big improvement in turning ability and holding high speed turns, but they can scrub off as much as 3 mph (depending on setting).

About Tuning and Instrumentation – We have spent many hours of testing with all these single pipe kits to assure the best possible performance and reliability. Despite that, there can be some subtle variations in the stock machines themselves that results in slight variations in performance with the kits installed. For the average recreational user, these variations are of minor importance. However there are many “enthusiast owners” intent on getting the most from their machines. For these owners, accurate instrumentation will be necessary to assure the benefit of adjustments and tuning. In particular the tracking of rpms, and peak speeds.

There are two popular digital tachometers used to track rpms. The $59 “Tiny-Tach”, and the $308 P.E.T. tachometers. The Tiny-Tach is very durable and affordable, however it has limitations. The Tiny-Tach update every 2 seconds, making for difficulty seeing accurate increases in rpm during acceleration. Once at speed, the T/T can offer accurate data, so long as the rpms are being sustained on a large section of smooth water. In rough water, the TT is incapable of yielding data that is accurate or meaningful.

While much more accurate, the PET tachs are less forgiving to heavy vibration and heavy water exposure. We consider them more as a tool for testing rather than a full time on board item. The PET tachs update every 1/2 second, allowing for very good tracking of rpm acceleration trends and immediate display of peak rpms. Like the T/T, the PET tach can only give meaningful data in smooth water conditions.

Radar testing has long been the standard for accurate speed measurement of pwcs, however the accuracy and durability of current GPS devices makes them a very effective “relative” speed measuring tool for watercraft. We recommend a GPS that can show real time speed to the tenth of a mile per hour (they are generally more accurate). When using GPS for speed measurement, it is essential to maintain the straightest possible path. Some GPS’s will show false reductions in terminal speeds when the machine is traveling on a radius or arc.