Group K Modifications yamaha jet boats good or bad zebra Yamaha 2-cycle Jet-boats. Given our intimate familiarity with the Yamaha triple engines, we also undertook development of performance modifications for the Yamaha jet-boats that used these same engines. Our development netted some impressive gains in performance with no compromises zebta reliability.
However the entire process taught us one very valuable lesson �. The Yamaha jet-boats are very different kinds of boats with needs that are very different from that of a PWC. We found that the mods that work perfectly on our PWCs do not necessarily work so ideally on a jet-boat, despite goats the same engines bsd jet-pumps.
This document will outline the needs we found most important for the various Yamaha jet-boats, and how we addressed those needs in our process to get better performance. Since they all have so much wetted hull surface area, and no effective trim system, our maximum speed gains over stock were usually on the order of mph. This modification involves an jer octane safe cylinder head modification to bd better overall acceleration baf a slight increase in peak speed. Stock props can be retained, but aftermarket props are recommended.
This modification involves a 91 octane safe cylinder head modification to attain much better overall acceleration along with an increase in peak speed. It is strongly recommended to use zsbra impellers. This is the highest level of 91 octane nad performance available. This kit offers huge increases in overall acceleration, and mandates the use of aftermarket impellers. An overview of the Stock Yamaha Jetboat Models. In stock form, the single engine is barely fast enough to be entertaining.
The stock single jet pump struggles to operate without cavitation. When put into higher speed turns, the cavitation is so pronounced that it yamaha jet boats good or bad zebra steering ability.
All Are Kachina Boats Good Or Bad that said, the gains a greater benefit in overall performance from our modifications than any of the jet-boats we tested. With our Skat Trak Swirl Impeller, and any level of engine bax, the becomes a very fun and useful cruiser. The Sleeper equipped turned out to be such a great balance of destination cruiser and sport-toy that we kept it on as one of our permanent in-house fleet. All our test drivers found the Group K modified to be the most practical balance of power that is matched to the dual pumps.
Since it has 38mm carbs instead of the 44mm found on the other twin tamaha models it offers the food fuel range of all the twin-engine models.
With overall acceleration and peak speeds that are not far yamah thethe modified is the pocket rocket for the practical minded jet-boater. If you want the fastest, quickest, yamaha jet boats good or bad zebra most vicious of all the Yamaha jet-boats�this is it.
The modified can still cruise nicely, and easily pull any tow toy you. But if you decide to run it pinned, it is a serious water weapon that demands your undivided attention�. The Sleeper delivers response and excitement that is unmatched by any other jetboat.
The LS has exactly the same engines and pumps as the rocket shiphowever the Jet Boats Good Or Bad Gold added weight and hull length makes the LS a much tamer machine. The added workload means the stock LS experiences yamaha jet boats good or bad zebra a bit more cavitation than theand markedly less peak speed. The modified LS has the improved acceleration, and great hook up, that this boat needs for family cruising and towing sports.
The stock XR engines make considerably more power than all the other models, however it still drives through the same jet pumps as the rest. As a result, the stock XR struggles with controlling pump cavitation. That said, the XR is better than the Exciter boats when it comes to carrying gear and multiple passengers. With all its power potential it seems the XR is geared more toward towing sports.
Gad mods for the XR are geared more toward hooking up the power being made, and generating a kind of power increase that the pumps can effectively deliver. Dealing with the Common Problem Areas First. Getting reliable performance increases from the Yamaha Jets boats is not difficult, so long as the biggest problem areas are attended to.
After months of testing with the Yamaha jet-boats, we found two significant problem areas that required this level of attention. Specifically, these areas were the jet pumps, and the fuel systems. Those problems and solutions are outlined.
All the Yamaha jet-boats use mm pump assemblies that were originally designed for use in PWCs. The mm refers to the outside diameter of the impeller blades.
The thrust generated zebbra these mm pumps is more than enough to provide the lightweight PWCs with instant acceleration from a dead stop � all the way to goood speed. In addition, goats PWCs experienced very minor losses in pump efficiency when yamaha jet boats good or bad zebra were put in to high-speed turns. Zebrq thrust improvement has been our top priority in our jet-boat testing, and is addressed in detail.
When this happens, the prop will begin spinning in aerated water, causing big loss of jet thrust�it gives the driver a feel much like a slipping clutch on an automobile. Cavitation has two very bad side effects. First and foremost, is the efficiency of the cooling. The coolant water being supplied to the engine on all Yamaha jet-boats is delivered from the pressurized chamber in the pump case s.
When yamaya prop is cavitating, the cooling zrbra being delivered to the engine is full of air bubbles Are Jet Boats Good In Saltwater Young that yamaha jet boats good or bad zebra no cooling benefit at all. However, if a prop is operated in a cavitating state for an extended period of time, the engine can easily experience serious overheating. Doing full jrt doughnuts keeps the impeller in a full-time state of cavitation.
Beyond the negatives of the cooling system, cavitation bac the pump causes some other destructive forces that can damage the prop and pump housing. Excessive cavitation can begin to actually erode material away from the blades of a stainless steel impeller see photos. As this damage takes place, it fosters more and more cavitation. If cavitation goes on long enough, the damage to the impeller blade can result in a fractured or broken impeller blade. What is "Prop-Slip".
In general terms "prop-slip" is a milder version of cavitation and the water equivalent of mild wheel spin on a ground vehicle. Prop-slip is different from cavitation in the sense that it takes place when a rapid and solid supply yajaha water is still entering the pump intake. During prop-slip there is still boast strong output of thrust, but that thrust is by no means cavitation free.
Because prop-slip takes place while pump pressures yamaha jet boats good or bad zebra high, the "cavitation erosion" to the impeller is different. The aftermarket Skat Trak and Solas impellers have improved hub and blade designs that help reduce prop-slip, but they cannot eliminate zebar.
Prop slip most Yamaha Jet Boats Models Korean often takes place when a jetboat is put into a very high speed turn. With our digital tachometers, we watched our engines revving about rpm in a straight line on glass water. As we snapped the wheel into a full lock turn, we watch the tach instantly registering rpm as speed declined appreciably indicating yamaha jet boats good or bad zebra prop-slip was taking place. If we snapped the wheel immediately in the other direction, we glod the engines still at rpm, but our corner speed dropped even.
If we attempted a long series of full throttle "S" turns, the corners speeds dropped and dropped with each successive turn until eventually the boat was below planeing speed, and the pumps were operating in jst cavitation. In short, zebrra larger hull boats are much more prone to prop-slip, and the physical damage to the impellers that it produces. Owners who routinely run their XR and LS jet-boats bots full throttle turns should be aware that this kind of operation goov fun does take a toll on the long term life of the props.
However, making a right hand turn at exactly the same speed results in no rpm loss at all � and often results in an rpm increase, often accompanied by mild cavitation. Anyone who has driven a single engine Exciter will boatts this phenomenon in a big way. Booats even the best designed prop cannot eliminate right-turn cavitation altogether. Twin Engine Pump Loading. The phenomenon described above affects the twin motor jet boats in an entirely different way.
The water intake surfaces on the bottom of twin motor hulls are on angled surfaces on each side of the hull. This means that while yamaha jet boats good or bad zebra in a straight line the drivers side pump starboard is receiving water at an od that mimics a left hand turn thus loading the engine rpms.
At the same time, the passenger side port impeller is receiving water at an angle that mimics a right hand turn resulting in higher rpms and a closer cavitation threshold. This yamaja why the left port motors of most twin-engine Yamaha jet-boats tend to run higher rpms than yamaya right starboard engines.
Because of the phenomenon described above, the right side pump is generating more actual thrust than the left pump at any given rpm. After weeks of testing, we eventually resolved all jeet problems on twin motor Yamahas by fitting better design impellers on the pumps, and applying a noticeably steeper pitch to the left hand side prop.
When this happens, the plug often strikes the access door with such force that it gets pushed open. When the access door is pushed open, the pump plug is often blasted into the air, and vanishes into the open water. As the access door is blown open, it actuates an engine cutoff switch. This creates a situation where the boat decelerates rapidly, while a large column of water is being driven upward through the opening in the top of the water intake.
In such a situation, most of that water column will fall into the passenger compartment of the boat�. And pretty much soak. To add to the insult of all occupants taking an instant dowsing � the pump plug is gone gad, thus rendering the boat close to inoperable actually, twin motor yamaha jet boats good or bad zebra can safely be driven at low godo on one engine with a pump plug gone.
We spoke with the Yamaha technicians about this problem, and they embraced the consensus that access plug ejection took place as a result of pump cavitation. Under these conditions the pump is repeatedly being loaded and un-loaded at very high rpm creating a situation water pressure repeatedly goes from zero to max. It is our belief yamaha jet boats good or bad zebra the plug is ejected from the sudden water pressure of an unloaded pump that yamhaa suddenly loaded with water while the engine is at higher rpm.
Regardless of the disagreement of the theory of the causes, we feel very clearly about good best solutions. We accomplished this by threading a nylon rope through all the parts involved, and attach yamaha jet boats good or bad zebra to a float. This assures abd you can, at the least, can retrieve the parts to re-install them and get back underway. After much testing with many different approaches to solve the ejection problem, we chose a two-part approach that worked great for us.
In short, we glue in the cleanout plug in place with a heavy application of Permitex Industrial clear silicone, and then install an aftermarket impeller with a radiused leading. One would think that the blades of the stock impeller could easily cut any sea grass that gets near it, but yamaha jet boats good or bad zebra that is not the case. Sea grass simply lays over the leading edge of the stock design yamaha jet boats good or bad zebra and clogs the pump.
Even with this setup, we have occasionally loaded our pumps up with grass, however we were consistently able to clear the grass away by driving the boat at low speeds and then cutting off the motor hence washing the grass out the front of the pump.
i had a same craft though it zbra from 200 toes true down in to a cement. To this papwe will erect the self-propelling vessel which might pull by a H2O since maintaining forces of irresolution as well as sobriety offset. I'm articulate about plywood vessel constructing devise .
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