The first ’99 XLL1200s arrived in showrooms in spring 99. As we would learn later, these first production XLLs were equipped with cdi boxes containing an "early version" ignition curve mapping (we don’t know how many units). Later production XLLs had a slightly changed ignition curve (that we presume to carry slightly more advance in mid-range areas). While these mapping changes made for very subtle differences in stock form, they make for very different detonation risks, and specification requirements, in modified form.

The 2 test XLLs we obtained in spring 99 were both the "first unit" at two separate large Southern Cal Yamaha dealers, and we presume "early map" versions. Subsequent testing with "later map" versions showed that some differences would be needed in our kit's specifications and equipment to maintain 92octane compatibility. Those changes (for the Sleeper kit) included the use of the stock arrestor case for better signal, changed jetting, different compression ratios, mandatory changing of the waterbox hose, and different impeller pitches. These changes are reflected in the text below. The overall performance of the early and late map version Sleepers is nearly identical. As of this posting, all modifications will be based on late map specifications (which work on both version machines).

The Stock Machine – The Stock XL Limited is designed and intended to be a top-notch rough water 3-seater. Unlike most rough water 3-seaters, the XLL also has the ability to turn exceptionally well.

From an engine standpoint, the new design 155 hp engine is very exceptional because it complies with EPA 2004 emissions mandates while still making very respectable power. Despite the power of the XLL’s new motor, the large heavy hull can easily give a feeling of serious "underpowered-ness". The XLL’s good rough water handling characteristics are the result of a large and heavy hull that has a lot of "wetted" contact surface area. When the boat is pushed into a turn, that further increases the amount of wetted hull surface, thereby further increasing drag. All this wetted area, during turning, causes the engine rpms to labor down to the point where there is not enough power to accelerate from a turn with strong authority. The only way to overcome this problem is with an overall increase in horsepower.

When riding the XLL at speed in a straight line, the hull has a feeling of "nose-heaviness". When conditions become extremely rough, this nose heaviness can make for a rough water ride that feels very "punishing".

The Group K Kits - While the XLL does experience some level of success in endurance type racing, this is a machine that will never stake it’s reputation as a full out racing machine. Most XLL owners are intending to build a quick and reliable high performance recreational machine … not a race boat. In addition, the XLL motor is built around a carburetion and exhaust system that is designed to be "emissions conscious". Circumventing these systems leads to "side effect" problems that most owners do not wish to deal with.

Knowing all this, the performance goals of our kits were simple … Increase overall acceleration ability (especially off turns), and increase peak speed ability. More importantly, we wanted to reach these goals without excessively expensive components, and without making compromises in reliability. The Group K "Limited" and "Sleeper" kits fit all these mandates. The performance info is as follows:

Limited Kit – Our most basic XLL kit is easy to install, and nets a good increase in acceleration and speed. Can be used with a stock impeller or the Solas 12/18 Concord.

Sleeper Kit (92 octane) – With the addition of careful cylinder porting, the XLL gets a big increase in low-end and mid range power that allows for the use of the more aggressive (less cavitation) impellers.

Sleeper 100 (octane) kit – Basically our Sleeper kit with additional porting and a higher compression ratio that allows for the use of even more aggressive impellers. This is the kit that took the overall win at the 1999 Salton Sea 300 mile Endurance Challenge.

Handling Issues – Like all pwcs, increased horsepower and speed abilities can have a significant impact on handling characteristics. The biggest advantage of the increased power of the Group K kits is that the XLL "steers" much better with the extra thrust. That is, the extra thrust allows the rider to turn the XLL much more precisely, and the extra power itself offers a big improvement in handling control. At the same time, increased speed can sometimes create new handling problems that must be attended to. Such is the case on the XLL.

Scoop-Grates - When the speed of the XLL hull is increased, the nose of the hull rides slightly higher than stock. When the throttle is suddenly closed at high speed (as would be done setting up for a turn), there is a sudden weight shift from rear to front that drives the steering edges on the front of the hull into the water. When the XLL is modified to run faster than stock, this weight shift is much more pronounced. It can happen that this weight shift drives so much of the steering edges into the water that the machine can engage a turn "much sharper" than the rider may have intended. This phenomenon makes it virtually impossible to predictably turn a more powerful XLL with accuracy and confidence at high speeds. Fortunately there is a single bolt-on part that completely eliminates this problem.

The R&D Aqua-Vane scoop-grate makes a profound change in the "rear-to-forward" weight shift when decelerating from high speed. The effect of the R&D grate is so significant that our test riders were unable to induce "any" of the previous high-speed steering variations. At the same time, the R&D grate offers better pump "hook-up", and a peak speed increase of .3-.5 mph. Given all this, we consider the R&D intake grate to be an absolutely mandatory modification for every 1999 XLL in existence. Group K will not perform modification work for any XLL unless the R&D grate is also fitted.

Ride Plates - As of this writing, there are no commercially available replacement ride plates for the XLL. Given that, Group K has developed an affordable modification for the stock ride plate that results in a significant improvement in peak speed and handling comfort. Our modification allows the nose of the hull to ride slightly higher in the water. This raised-nose attitude makes for slightly less "wetted" hull surface, and thereby less friction against the water … allowing for a measurable speed increase. At the same time, the raised nose allows the hull to "loft" over rough water (as a dirt bike would loft the front wheel over rough terrain). The result is a much less punishing ride from the large XLL hull.

Exhaust System – The stock exhaust system of the USA-version XLL is the first pwc to employ a catalytic converter for the purpose of reduced emissions. This cat-con exhaust system is also fitted with heat sensors that "talk" to the other electrics on the engine. If these sensors are not satisfied (by the high temperatures of the cat-con), the ignition will not offer the correct firing curves for optimum performance. Given all this, Group K has chosen to leave the XLL exhaust pipe (and cat-con) completely stock.

The hose between the waterbox-muffler and the hull exit, on the XLL, has a large attached plenum chamber to improve silencing at certain rpms. This entire hose can be replaced with "straight through" waterbox hose from a '98 XL1200. The installation of the '98 hose on the XLL does not make a big difference in speed or sound level. However the '98 hose does make a very significant change in exhaust back-pressure. This back-pressure has a significant effect on mid-range engine temperatures, and detonation risk. The benefit is so significant that we recommend the '98 hose as a mandatory upgrade for all our XLL modification sets.

About Triple Pipes – Factory Pipe Products manufactures a replacement exhaust system for the XLL that employs the use of three individual expansion chamber bodies. While the price tag of this exhaust system is considerable, so is the horsepower increase ($2500; 50 hp). If this system could be installed as an individual modification, it would be a very practical option for many XLL owners. Unfortunately, getting the triple pipes to work well is a bit more complex than that. No one has yet found a way to satisfy or bypass the aforementioned heat sensors that tell the stock ignition system to give a favorable high output curve. In addition to this, the added rpms of the triple-pipes require an ignition curve that has much more retard than the stock unit. To date, the only solution to these collective problems is to install a programmable MSD total loss ignition. While these ignitions can yield excellent performance, they do not have a charging system of any kind. The battery energy used to make sparks is totally lost without being replenished (hence the term "total-loss"). Group K has been involved in the testing of these "triple-pipe / total-loss platforms. While they yield phenomenal performance, the long term reliability (and the complexities of the ignition) are not yet what we consider "recreational friendly". As further development of this platform advances, we will be posting a "triple pipe" document to our website.

Carburetion – The XLL uses the same 44mm "I" body Mikuni carbs as are used on the GP 800. These carbs offer very good performance, as well a fuel delivery curve that helps satisfy EPA emissions mandates. Unlike the GP 800, the carbs of the XLL have adjustment screws with "tamper caps" pressed over the top of them. These caps can be removed, allowing for the adjustment of the high and low speed adjusters.

Most 1999 XLLs appear to have carburetion that is somewhat over rich. In the case of other over rich pwcs, such a problem is commonly solved by the installation of a free-er breathing aftermarket arrestor. There is a commonly held belief that free breathing flame arrestors resolve rich conditions by accessing more air to go along with the fuel … this is not true.

On board fuel flow meter tests show that the installation of a free breathing arrestor reduces overall fuel flow between 5%-15% at various throttle settings. This happens because the inlet tract vacuum (aka signal) that pulls fuel from the carb metering circuits is much lower with a free breathing arrestor. If the net effect was an even 5% fuel reduction at all throttle settings, this mod would be very viable. Unfortunately, the emissions conscious "I" body carburetors employed on the XLL can experience much more serious lean conditions a specific throttle openings in the mid-range that cannot be corrected by jetting.

During testing with our kits, we achieved our best fuel flow results on our 92 octane kits by retaining the stock arrestor case, but removing the air inlet hose and forward mounted plenum chamber. This allowed for improved air access, and a level of signal reduction that could be corrected by jetting. (for 92 octane). The additional octane of the Sleeper 100 kit offers an easy safety margin from detonation, hence we recommend the R&D arrestor for the Sleeper 100.

All our XLL kits, to date, retain the stock carb throats with choke plates intact.

** For more info about "signal", refer to our website document titled "Racing Carburetors 1999"

About Larger Carbs – Installing larger carbs has been a popular modification for many high performance pwcs. We have chosen to not utilize aftermarket carbs on our XLL Limited and Sleeper kits for a few reasons. First and foremost, the location of the carbs underneath the stock exhaust pipe makes it virtually impossible to reach the adjuster screws of all three carbs. This means that the pipe body must be removed to make uniform carb adjustments (no small job). Beyond this, larger carbs will generally result in significant increases in fuel consumption, and an obvious reduction in fuel range. Since fuel range is a pivotal concern for many owners, we feel that the reduced range of larger carbs would be hard to justify in most riding applications.  Finally, we question the need for larger carbs on platforms using the cat-con.

A large part of our triple-pipe testing has been conducted with the stock 44mm "I" body carbs. Even on the triple pipe platform, these carbs offer an excellent balance of strong overall power and "reasonable" fuel range (on 100 octane). Larger carbs did offer slightly better peak rpms. However those rpms came at a considerable cost of range.

Compression – The XLL responds very well to increases in compression … within limits. Our Limited and Sleeper kits have been developed to run the highest compression ratios that we consider to be 92 octane pump-gas safe. We attain this higher compression by machining the stock cylinderhead (a much more affordable alternative to buying another head). After milling the stock head, we also recut the domes for a shape that better staves off detonation. The specification of the Limited and Sleeper modifications are different, however the Limited modified head can be re-cut to the Sleeper spec. Because of variations in starter cranking speeds, compression gauges, and measuring techniques, we do not specify the compression of our different arrangements in terms of "psi" pressure readings. Our technicians do not discuss any compression specifications of these kits in terms of psi or ratio … please don’t ask them to.

About "O" Ring Sealing – Some performance shops manufacture "billet" replacement cylinder heads known as "O" Ring Heads. These heads are manufactured to utilize a large diameter rubber "O" ring to seal between the cylinder and head (instead of the stock metal head gasket). This "O" ring system can offer great convenience to owners who regularly remove the head for the purpose of inspection or compression changes (in the case on changeable dome heads). The other big plus to the "O" ring setup is that it significantly reduces squish clearance without having to machine the top surface of the cylinder. This "O" ring system is the means of head sealing on stock Sea Doo and Polaris engines.

It should be understood that an "O" ring can easily seal water away from the cylinder bores, however no "O" ring on earth is strong enough to seal back the pressures of compression. Original equipment "O" ring setups depend on a relatively broad metal-to-metal mating surface around the bore diameter to seal compression. The absolute flatness of the surfaces on the head and the three cylinders of the XLL is fundamental to maintaining a lasting long-term seal. Herein lies the problem with some aftermarket  "O" ring head setups. The three cylinders must have perfectly flat (preferably lapped) surfaces on their top "head sealing" surface. These three cylinders must also have the exact same deck height to keep from flexing or distorting the one-piece head. The stock metal head gasket has the ability to more effectively accommodate all these possible surface variations. For this reason, all Group K kits are prepared to utilize the stock metal head gasket.

About Spark Plugs – Unlike most other pwcs, the XLL has very high output ignition capable of firing a spark across a .044" plug gap. This larger plug gap is a big asset to the performance of this engine. The spark plugs used in the XLL are a NGK BR8ES-11. These plugs are the same as the more common BR8ES in every way … but one. These "11" series plugs have a ground electrode with a different radius bend that allows for an accurate .044" gap. If you try to gap a conventional BR8ES to .044", the ground post will be bent in a way that does not allow for consistent firing. If you have an XLL, use the "11" series plugs gapped to .044".

Cylinder Porting – The cylinders on the XLL are unconventional by pwc standards. Instead of an aluminum cylinder with a thick iron sleeve, the aluminum cylinders of the XLL have a thin layer of hard plating for the piston to reciprocate in. Yamaha calls this plating "Yamaha Ceramic Coating", but it’s basically "Nicasil" (a nickel-silica plating). This thin, but super tough, bore diameter has a much lower friction coefficient than iron, thus allowing for much quicker piston acceleration. This thin plating also makes for a much more conductive-friendly path for the heat of the piston to get to the water-jacket. The material of this plating is so tough that it can stand up to the forces of several piston scoring "episodes" with virtually no damage to the bore at all.

The only down side of the plated bore is the inability to be "bored-oversize" after an engine failure. In situations of minor damage to the plating, re-plating of the cylinders is available from the aftermarket. In the event of a major failure, the cylinder must be replaced.

All this begs the question, "what about cylinder porting?" Plated cylinders, like those on the XLL, can be ported. However special attention (and special cutters) must be used to assure that the plated liner is not compromised. The cylinder porting used in our Sleeper kit is not "radical", so it does not represent a risk to the integrity of the plated liner. We would accent that the porting of plated cylinders should only be done by experienced technicians. At Group K, we have many years of experience performing cylinder porting on plated bore cylinders, like those on the XLL.

In the past, cylinder porting has received an undeserved reputation as a modification that harms low end power and reduces engine life. This may be true for poorly executed portwork done by folks with little experience. However quality cylinder porting can be tailored to create an accent toward any kind of horsepower need. Our cylinder porting modifications for the XLL carries an accent towards strong middle to high range power to help drive the hull off the turns. At the same time, the excellent low-end acceleration is fully maintained. An unintended benefit that comes along with this porting is the added high range torque that increases the peak by 100-150 rpm.

Our cylinder porting is available in two different finish modes. Both the "Recreational" and "Competition" finish modes include all the same port timing, port shaping, and specification work. The Competition mode also includes additional exhaust port finishing and a transfer port "rough finish" that further improves fuel atomization. This additional finishing work accounts for 30% more shop time, yet contributes to only about 10% of the total performance gain (about .5 mph and a little bit of acceleration). The recreation finish is standard in the Sleeper kits, the "Competition" finish is available as an option. The cost difference...$700 vs $450.

To assure that the modified cylinders will have the correct compression ratio and squish clearances, we modify the cylinders and cylinderhead as a matched set only. All ported cylinders are also honed.

About Pistons – As previously mentioned, the plated cylinders of the XLL cannot be bored, but that does not mean that there are no oversize pistons. The cylinders on the XLLs vary in diameter over a very narrow range (a few thousands of an inch). To accommodate this variations in diameters Yamaha has four different "standard" pistons for the XLL (denoted as a0, b0, c0, d0). When replacing pistons, be sure that you are re installing the correct "standard" piston for that cylinder.

While the plating on the XLL cylinders cannot be bored, they can be honed. This means that if you experience some kind of piston scoring, a small amount of material can be honed out of the XLL cylinder to offer a good clearance fit to a slightly larger Yamaha piston. Please note that there is only one piston ring size to cover all these piston diameters.

About Rev Limiters - As mentioned above, our kits utilize the stock ignition system. This ignition has a rpm limiter that offers very "unfriendly" ignition firing at about 7450 rpm. It often happens that a modified machine running close to the rev limiter can have speed difficulties in rough water. When the prop comes "un-hooked" at high water-speeds, the engine immediately bumps the rev limiter. If the pump reconnects with the water while the ignition is "on the limiter", the rider can get a sensation that feels like "landing with the brakes on". In truth, the rider is experiencing the moment that it takes for the engine loading to pull the engine down away from the limiter. The 99 XLL has an additional "limiter" whereby the cdi box also signals the exhaust valve servo to "drop the valves" when the rev limit is reached. This gives the XLL an uncommonly strong "landing with the brakes on" feeling. Our Sleeper kits easily make enough power to run close to the rev limiter. As such, they are also capable of experiencing this very strong "landing with the brakes on" feeling at high speeds in rough water that (caused by the valves dropping at the rev limit).

To abate the "valve dropping" limiter feature, Riva manufactures a kit that converts the exhaust valves to a (simpler) pressure control system. This easy to install kit eliminates the valve linkage, servo motor, and electrical driver … as well as the "dropping valve limiter" feature. With this kit in place on our Sleeper kit, overall acceleration is unchanged. However there is a huge improvement in the engine’s ability to maintain steady speed at high rpms. While the Riva Valve kit is not inexpensive ($690), it does forever eliminate the need to maintain the cables, linkage, servo, and electrical driver. We strongly recommend this upgrade for any XLL owners experiencing valve train malfunctions, and/or any owners intending to use their XLL sleeper for high-speed rough-water applications.

About The Pump – The pump on the XLL utilizes a 155mm impeller (the same diameter used in earlier Yamaha 1200 models. However, since the XLL prop mounts on a larger threaded shaft, and has a different "back-set", the impellers from previous year GP1200s cannot be fitted to it. The 155mm pump is among the largest in the industry. However even with this large diameter pump, the XLL experiences a considerable amount of cavitation. Part of this cavitation is a result of a sealing breech between the impeller housing and the pump shoe mounted directly ahead of that housing. Another part of the cavitation is caused by insufficient water supply at the pump inlet, and excessive clearance between the impeller and it’s housing. The installation of an R&D grate can improve water inlet, and impeller resizing can further improve the hook-up.

However even with all these improvements, a perfectly prepared XLL pump will still experience "some" cavitation upon initial takeoff. This cavitation is simply a function of a slightly undersized pump that is trying to push a very large and heavy hull up on to plane. The worst part about this on-going cavitation is that it causes visible damage to the impeller blades. This damage (known as "prop burn"), looks like a sand blasting type of surface erosion on the outside diameter of the impeller blades. This erosion is self perpetuating, so it helps to create more cavitation … more erosion, and so on.

The Skat Trak "Swirl" impeller offers considerably better initial take-off, and rough water hook-up, than any other impeller. However the Swirl inflicts a peak speed loss of 1.5 – 2 mph. Despite this, we consider the Skat Swirl an ideal choice for owners who use their XLL exclusively for towing sports, or for repeated low speed "rough water" acceleration.

In spring 2000 Solas released their "Concord" series of impellers for the XLL. The two available Concord pitches are the 12/18 and the 13/19. Both pitches offer a significant improvement in overall hook up (especially on take off) compared to the modified stock prop, but not quite as good take off as the Swirl. In addition, these Concord impellers do not have the peak speed loss of the more aggressive Skat Trak Swirl. The 12/18 is ideal for our "Limited" XLL kit and for Sleeper kit owners. The higher 13/19 pitch does not offer near the strong acceleration of the 12/18 (on the Sleeper 92), but it can be an effective choice for Sleeper owners whose riding is primarily solo and high speed. The 13/19 is highly recommended for the Sleeper 100 (octane) kit.

Note: Any aftermarket impeller change will require an impeller tool and a driveshaft holding tool.

About Marina Gas - There is a great convenience to buying "on water" marina fuel for machines that consume as much gas as these boats do. The unusually high price of marina gas is not a reflection of that fuel's high-octane quality. The high price is more a reflection of the dock master's awareness of how captive his customers are. In any case, the normally low grade of marina fuels can work fine in the low rpm, low power output motors in most boats. However, a Sleeper kit triple needs much better octane than most marinas offer. Unless you have personal knowledge of the quality of the marina fuel at your ride spot, we would recommend to not use it for extended full throttle or competition type riding.

By far the most cost effective octane option is 100-octane aviation gas. A gallon of 100-octane "av" gas costs about 50 cents more per gallon than 92 octane unleaded. Another option is a 50% mix of 110-octane race gas with 92 pump. Either one of these choices will yield the needed octane level.

Lots of owners ride in areas where they need to buy fuel at outlets on the water. These folks are more interested in octane "boosters" that they can carry along. Unfortunately no octane booster can turn 92 octane into 100. At best, 3 oz of booster per gallon can normally make 87 into 90, or 92 into 93.5-94 (the increase offered by booster becomes less as base octane gets higher). Using more than 3 oz per gallon offers no further increases. In addition, this small increase comes at an expensive $1 per gallon additional.
About Teardown and Assembly – The teardown and assembly of our XLL "Limited" kit can be done by owners with basic tools and basic mechanical skills. The Sleeper kit requires the removal of the cylinders and the carburetor bank. Because of the added linkage hardware that operates the carbs and the exhaust valves of the XLL, this teardown and re-assembly requires a higher level of mechanical ability and expertise. If you doubt your ability to correctly reassemble these components, we recommend that you have the job done by an experienced technician.

"Limited" Spec Cylinder Head Modification 180.00

R&D Scoop Grate 99.00

Group K Ride Plate Modification 60.00

Optional Skat Trak Swirl Impeller (13/20) 233.00

Optional Impros Type 1 Modification (clean prop) Smooth-water/towing use 65.00

Optional Impros Type 1 "Worx" Modification (damaged prop) Smooth-water/towing use 89.00

Optional Solas 12/18 impeller (with impeller tool) 229.00

Driveshaft Holding Tool 11.00

Cylinder head modification, and Carb Jetting, cover cap removal / Inspection

Optional Competition Porting Finish additional 250.00

R&D Scoop Grate 99.00

Group K Ride Plate Modification 60.00

Impros Type 1 Modification (clean prop) rough-water solo use 65.00

Solas 12/18 impeller (with impeller tool) (towing use) 229.00

Solas 13/19 impeller (with impeller tool) (high speed solo use) 229.00

Driveshaft Holding Tool 11.00

Optional Riva Exhaust Valve Kit 690.00

Optional Skat Trak Swirl Impeller 13/21 233.00

Optional Impros Type 1 "Worx" Modification (damaged prop) rough-water solo use 89.00

Optional Skat Trak D-75 Magnum pump with Swirl Impeller (exchange) 1340.00

Optional Skat Trak D-75 Magnum pump with Swirl Impeller (no exchange) 1715.00

Cylinder head modification, and Carb Jetting / Inspection

Optional Competition Porting Finish additional 250.00

R&D Flame Arrestor 216.00

R&D Scoop Grate 99.00

Group K Ride Plate Modification 60.00

Solas 13/19 impeller (with impeller tool) (high speed solo use) 229.00

Driveshaft Holding Tool 11.00

Optional Riva Exhaust Valve Kit 690.00

Optional Skat Trak Swirl Impeller 13/21 233.00

Optional Skat Trak D-75 Magnum pump with Swirl Impeller (exchange) 1340.00

Optional Skat Trak D-75 Magnum pump with Swirl Impeller (no exchange) 1715.00

**NOTE: Group K will bill an additional $35.00 handling charge for engine assemblies via UPS

ORDER INFORMATION: SEND ALL PARTS REQUIRED FOR MODIFICATION VIA UPS TO:

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.