Most Mercury Sportjet boat owners want to perform at least a certain amount of their boat maintenance themselves to ensure continuing good performance and reliability. The more technical work should be done by a certified Mercury technician who has the skills and diagnostic tools to troubleshoot and resolve issues with the different systems. Our Certified techs have over 100 years of combined experience in the event you need a higher level of assistance. To avoid unnecessary trips to the service center, it might be useful to have a checklist which can be run through systematically, in the hope of pinpointing problems quickly. The boat can be divided into three categories – jet unit, engine, and hull. If something is “wrong” with the boat it is usually poor acceleration and load carrying, coupled with excessive fuel consumption or engine RPMs. It could be unusual noise coming from the mechanical, or possibly just poor holeshot or top speed. All of these things may be present to some degree, but the usual complaint is that the boat “doesn’t run like it did when I first got it.”
The most important single instrument on the boat when considering performance drop-off is the tachometer. The great thing about jet boats is that the engine RPM’s should remain the same throughout the life of the boat, regardless of age, loading, water conditions, whatever. Your Sportjet engine should top out in the 5500 RPM range, give or take 150 RPM depending on the specific engine (Check your manual for your specific model. ie 175hp. 200, 210, 240, or 250hp). Most of our newer Sportjet powered boats are equipped with the Mercury Smartcraft Gauge. These gauges come in different flavors, from basic to giving you detailed info like fuel flow data, water temperature, water pressure, RPM, and even a diagnostic center. The most common system we now use in most of our boats not only sends a specific series of beeps for events like low oil, low voltage, or water in the gas, they actually give you the information on the screen in addition to the alarm code. Remember, a constant horn only means one thing, OVERHEAT. So take that code very serious. There is no situation where the RPM’s should be different from when the boat was new, and as an owner, you will know what these are. At any time, you should be able to open the throttle fully and get exactly the same maximum reading you have been used to. Or perhaps you are finding it needs more RPM’s to cruise with your normal load. RPM’s are a most important indicator of proper operation of the boat.
A. Normal maximum RPM = hull problem.
If the boat is performing poorly and the maximum RPM’s are normal and what you are used to, you can look to the hull and some of the external parts. These include:
B. High rpm = jet unit problem.
Higher than normal RPM’s, lack of thrust, slipping clutch feel, trouble getting a load up.
C. Low RPM = engine problem
There is generally no way the jet unit can overload the engine and bring the RPM’s down. If the RPM’s are down from usual, it is almost certain to be an engine problem. A compression check will usually reveal leaking piston rings but is unlikely. The most common reasons for reduced engine power are:
Provided your engine is getting its full quota of air and fuel, and is getting enough spark and at the right time, the engine will usually be OK, and maximum RPM’s will result. However if the RPM’s are down and you believe the tachometer, look for an engine problem.
Starting issues: While the earlier carbureted version of the Sportjet engines can be hard starting or cold blooded like any carbureted two stroke engines, the Direct Injected 200hp Optimax should start quickly and flawlessly every turn of the key just like it did when it was new. If the engine does not start immediately, check the fuel supply first. From the fuel tank, most Optimax engines have a fuel separator filter, followed by an inline filter, fuel lift pump, and then the Mercury onboard fuel filter that has a water sensor at the bottom of it. Any blockage or failure of these fuel components can cause a hard starting or non starting issue. All filter elements should be replaced annually. In the event of a fuel lift pump failure, the system will typically not start, or start and not keep running after it does start. A good lift pump will have a “muffled clicking sound” when the key it first turned to the on position. If the engine will not start, and the clicking sound seems dry, or louder, it can indicate a faulty fuel lift pump. I carry an outboard style primer bulb and some hose clamps in my tool kit just in case of a lift pump failure. Of the three fuel pumps on the engine, the lift pump is the most likely to fail. Simply bypassing the lift pump with a primer bulb would offer a temporary method to get the boat started and running normally. (NOTE: The fuel lift pump requires special Odiker clamps and should be replaced by a qualified technician or with the proper size clamps and Odiker pliers, due to high fuel pressures.
Oil. Feed your two-stroke outboard bargain oil and ensure rapid aging. Don’t think you’re saving money when you buy some off-brand oil. To meet industry standards, oil has to pass the test only once, meaning it’s not monitored by the batch. Better oils are uniform, consistently meeting the standard case after case. During the average summer, your 200-hp engine may burn only 3 or 4 gallons of oil. The difference between cheap oils and the ones offered by engine manufacturers may be about $10. Remember: The most expensive thing you can put in an engine is cheap oil. We recommend Yamalube 2M or Mercury DI oil, and offer discounted bulk refill at our parts counter. (Save your clean jug)
Mercury Optimax engines have an oil injection system with a 3 gallon oil tank and a small engine mounted reserve on the engine. The main tank feeds the engine mounted tank, which will run only 20 minutes if your main tank runs dry. (This is when your “hey dummy” or low oil horn goes off (4 beeps every 3 minutes). I always carry at least a gallon of oil in my boat as back up. IMPORTANT: If your main oil tank runs out, you will need to do more than add oil to the tank. You will need to put the large oil cap back on the tank (make sure it is snug) then open the small cap on the engine mounted reserve tank, and start the engine. The main tank will feed oil to the reserve tank. Allow it to fill completely with oil, purging the air, and then quickly tighten the small cap. The low oil horn should stop and you can proceed. (usually takes 1-2 minutes)
After 15 years and thousands of hours of running the Mercury Sportjet engines, I have learned to always carry a few handy items in my toolbox. Of course, a complete tool set, including metric wrenches, sockets, screwdrivers, wire pliers, etc are important. In addition, I suggest the following items:
Occasionally something will get lodged in your jet that just doesn’t want to come out. Our 9 bar intake with stomp grate was designed to allow little pebbles to pass through, and for bigger rocks to be too big to enter. The most common size rocks to get stuck in between the intake bars are what I call “skippers”, or flat rocks that you might skip across a river. These rocks are typically about 1/2”” to 5/8” thick in the middle. They are easy to remove by shutting off the engine and simply stomping the stomp grate or pulling the helm mounted stomp grate lever. Once the stomp grate bars open, the rocks will sink to the bottom of the river. (Unless your engine is running!)
Sticks can get stuck in the intake, and can be removed just as rocks are removed described above. Occasionally small soft wood, driftwood, etc can get past the intake and lodge on the impeller or stator, creating turbulence and vibration immediately. Sometimes it can be severe enough so that the boat cannot maintain on-step performance, but generally the RPM increases and vibration is noticeable. This is more likely when a river is swollen and there is an excessive amount of debris floating on the surface. If this occurs, here are the list of the spets to take;
Grass is the enemy of most jets. The Sportjet intake is much larger than most boat intakes, like outboard jets, single stage axial flow pumps, etc. I have found that the Sportjet pump can still get on step and maintain plane even with the back 20-25% of the intake surface loaded with grass. In the event you get grass stuck in the intake enough to reduce your performance, stop the boat, turn off the engine, and stomp the stomp grate multiple times. It may take 10-20 stomps in some instances to rip the grass loose, vs the 2-3 times needed for rocks. You should be able to see broken grass blades floating up near the stern of the boat. Many times I have completed my trip and when I put the boat back on the trailer at the landing, I found handfuls of grass still stuck in the very rear of the intake. It is amazing to me the ability of this pump to perform even with that much grass blocking the water flow.
Loading a Sportjet boat on a properly adjusted boat trailer is almost effortless providing you do not make the same mistake that most boaters due. DO NOT BACK TOO MUCH TRAILER IN THE WATER! 1) Back the trailer in 90 degrees to the water’s edge. (Never angle the trailer downstream- it puts one wheel lower than the other) Back up trailer until the rear 12”-18” of the bunks are just under the surface of the water, no more. The trailer should look very dry, and almost as if there is not nearly enough trailer in the water for loading. Approach the trailer slowly, at about a 45 degrees angle facing upstream. Once the nose of the boat is “cradled” in between the bunks, turn the steering wheel downstream and slowly increase throttle. As you feel the boat nose centering on the trailer toward the roller, increase RPM even more until the boat is at or very close to the roller. Leave some throttle on and have someone secure the strap. (Remember the strap always goes under the roller, not above.) Chop the throttle, kill the engine, and winch the boat the final few inches so that it is tight against the roller. The wife will be so impressed!