TROUBLE SHOOTING CHECK LIST

Excess RPM's

Using the jet drive as a dynamometer, excess RPM's must indicate one thing.  Something is preventing the jet drive from absorbing the power available according to the Impeller Horsepower Absorption chart.  Here are the most common problems:

1.  Debris in the jet drive.

The boat takes a log of RPM's to get or stay on plane, or may not get on plane at all.  There may be accompanying vibrations or water thudding noises as well.

Cure

Shut down the engine.  Remove the ignition key.  Probe the intake area to see if something is hung in the grate.  You will have to go overboard so first - try this;  sometimes just shutting off the engine and restarting it will do the trick, especially if there are large weeds or a plastic bag sucked up against the grill.

If the slippage is still there and the grill is clear you probably have:

2.  Something in the impeller.

To inspect the impeller you will need to remove the hand hole cover.  Use caution.  Your jet may be below the static water line.  Remove the cover and you risk flooding the boat.  If this is the case, beach the boat so it cannot sink or limp back to the trailer.

Invest in an extension for your inspection hand hole if it can be fitted.

Owners of transom mount "E" & "F" models are OK.  Your hand hole is outside the boat.  It may be difficult to get to, but there is no danger of flooding the boat.

Once the hand hole is open, feel all around the impeller for a small stick, piece of plastic, rock between the impeller blades or even ski ropes or long weeds wrapped around the impeller shaft.

Remove any debris you find, reinstall the cover and try to accelerate.  If you are still slipping, you probably have something lodged way back in the impeller blades.  Take another look!

Also check the impeller blades to see if there is a piece missing!  This is very unlikely, but an ingested rock can break a blade.

3.  Wear Ring Clearance

The wear ring acts as a seal between the high pressure water in the impeller, bowl are and the low or no pressure water in the suction piece.

If the wear ring is loose, there will be excess back flow of high pressure water and you will experience the following symptoms.  Any or all of:

1. Loss of a few MPH on the top end.
2. Require more RPM's to maintain the same cruise or ski speed.
3. On hard acceleration, you will get several hundred RPM's overrun, then the engine will load back down to normal or slightly higher RPM's.

The only cure for a worn wear ring is disassembly of the bowl and impeller and replacement of the wear ring.  Sometimes the impeller skirt (seal) area will be worn excessively as well.

4.  Worn or Dinged Impeller

Operations in sandy, rocky or dirty water will cause the leading edge of the impeller blades to be dinged off.  After awhile the edge is no longer almost sharp, but rounded off or even chipped or dented.

The symptoms of a worn impeller are the same as for a worn wear ring.

Diagnosis is simple.  Feel the impeller blades through the hand hole or look at them through the grill with a flashlight to enable you to see the impeller.

If the edge is rounded, bumpy, chipped or has other damage, the impeller must be removed and either replaced or the edge rounded to its original contours.

Generally, an impeller overhaul and fitting of a new wear ring is all you will require to restore as before performance to your jet drive.

If your outfit was purchased used, and you have always had RPM's higher than the impeller curves indicate you should have, this simple overhaul may give you performance you never knew you had.

High Horsepower and Big Loads

Occasionally you will load up all your gear and crew in order to make one run to the campsite across the lake.  If you hit the throttle hard at low speed you may overpower the impeller and cause it to cavitate.  Usually you can accelerate easily and get up on plane without over revving.  If you cannon, either reduce your load or operate at suitable reduced throttle.

In the event you have a worn impeller or wear ring, sudden high RPM's at off plane boat speeds will induce cavitation much faster than when your jet drive is like new.

Operator Suggestions

Do not accelerate at sudden high RPM's when in shallow water.  The suction will pull sand, mud, sticks, leaves or rocks into the jet and either promote rapid wear ring and impeller wear or leave you with debris in the impeller.

Air Ingestion

There are several types of air ingestion.

a.  The first air ingestion is caused by the impeller packing being worn or loose.  This air ingestion will be under high throttle acceleration.  The suction of the impeller causes air to flow into the suction piece between the impeller shaft and packing.

A typical symptom of air ingestion of this type is high RPM's on acceleration which drop once the boat is at speed.

Usually worn packing will be indicated by leaking at the packing gland both at rest and at speed.

Replace the packing or tighten the packing gland.

b.  Certain boats will induce air ingestion at speed by funneling air down the edge of the keel, a strake, or past a thru hull fitting.

Air ingestion of this type is usually indicated by proper acceleration and load RPM's than an increase in RPM's with either loss of speed or no speed increase.

Sometimes a slight turn will make the tendency worse or performance may actually increase if the air stream is deflected away from the intake.

The remedy is to remove the air trap or modify the water flow down the boat bottom so this air is deflected towards the chines and away from the intake.

c.  At speed some boats become so loose and free running there is no hull in the water to make a smooth water flow, high pressure path for water to follow into the suction piece.  The flatter the bottom (less dead rise) the sooner this problem will develop.

The symptoms are rapid and frequent momentary jumps in RPM's as the impeller grabs air, unloads, the grabs water and reloads.  Aside from accelerated wear on the thrust bearing and impeller, the condition contributes to excess RPM's and blown engines.

If you operate on choppy or rough water at high speeds and experience this type of cavitation, you can either slow down, keep a very quick throttle foot or hand, install a RPM limiter set 200 to 400 RPM's above your normal RPM's or plan on bent pushrods, floated valves and broken connecting rods.

7.  Loss Of Speed

See items 1 thru 5.  If none of these account for the speed loss then look at these items.

1. Reverse gate has slipped down and is dragging in the jet stream.
2. You added weight to the boat.  Speed is a power to weight relationship so every extra pound of fuel, gear or whatever costs a bit of speed.
3. The bottom of your boat has changed due to trailer sag, broken bunkers, etc. and the boat will no longer ride as free as it originally did.

Restore speed by:

• Losing weight
• Fix the trailer
• Straighten the boat bottom
• Adjust the reverse gate-shift cable linkage

Loss of Engine RPM's

Again, remembering the dynamometer theory, loss of RPM is either due to loss of engine power or internal friction in the jet drive or drive shaft.

1.  Poor fuel, water in fuel, old fuel, engine fuel system problems, plugged filters on fuel tank suction tube;  check fuel flow!

2.  Engine out of tune.

1. Check tuning, dwell, plugs, compression, etc.
2. Has the throttle linkage slipped so W.O.T. is no longer possible?

3.  Engine is overheating.

1. check for free water flow through the block.  A garden hose on the inlet water line will let you see if you have water flow.
2. Is there water flow from the pump into the cooling hose?  Leaves or gravel can get into the supply line.  Clean it out.
3. Did the flow valve (if you have one) vibrate itself into the off or low flow position?  Adjust it for proper flow then use a tie wrap to fix it so it cannot open or close.
4. Blown head gaskets or exhaust riser manifold gaskets can let high pressure gases into the engine cooling system.  Check for water in the oil, water fouled spark plugs.

4.  Bad Thrust Bearing

If the thrust bearing is failing or locking up the friction will pull the engine down.

Check if the bearing is housing is hotter than usual.  It should be cool or warm to the touch.

Listen for rotating noises such as squeaking, grinding or a rough vibration.

Note:  A failed thrust bearing can lock up and you will twist the impeller shaft or it will let the impeller shaft ride forward and the impeller will eat itself up on the wear ring and suction piece.

The forward thrust can force the crankshaft forward and put excess strain on the main thrust bearing.

If you suspect a bad thrust bearing, come home easy and save some big bills for parts other than a new bearing.

5.  Something Wrapped in the Impeller Shaft

If you pick up lots of fishing line, a floating rope or your ski rope, it can wrap up and fill the suction piece cavity or get between the wear ring and impeller.

Remove the item through the hand hole opening using a sharp knife, hack saw blade, etc. to cut the mess loose.  sometimes it is necessary to pull the bowl and impeller.

LOSS OF BOAT SPEED - Constant RPM's

When you experience a reduction in boat speed, yet your full throttle RPM's are the same as before it is safe to initially assume there is nothing wrong with the jet drive, at least as far as it's internal condition is concerned.  Once again, please remember the Dynamometer theory.  The jet drive is absorbing the same power, at the same RPM's so it is putting out the same amount of thrust.  Before you head off for a jet drive overhaul, take a look at these areas:

1. Have you added an extra fuel tank, started carrying two new sets of water skis, changed weight dramatically of any of your passengers or purchased a new 68 quart cooler?  The speed of your jet boat is primarily a function of power to weight ratio - if you added weight, especially towards the bow, you will use speed - a little or a lot, depending on how much weight and how it effects your craft's Longitudinal Center of Gravity (LCG).
2. Check your reverse gate and make sure it does not drag in the jet stream.  Any drag is an application of reverse thrust and down goes your speed.  Adjust your cable linkage, check for loose connectors, bent control pivot arms, loose bushings in the reverse gate pivot pins.
3. Bottom spray drag can also slow you down.  Perhaps water is hitting the reverse chute since you raised your cavitation plate, or you installed a drop nozzle and now the whole steering section drags at speed.
4. A common cause of lost speed is the development of a hook in the running surface.  Over a period of time trailers may sag, support bunkers break or one is knocked out of adjustment and the hull takes a new shape.  If you get a hook in the last eight feet of running surface there will be a tendency for the hull to run flatter, move glued down, and the extra bottom drag slows you down.
   
   The remedy is simple but involves lots of work, expense or both depending on how bad, who does the work and how exact you want the bottom blueprinted.  Taking out a hook or straightening crooked running surfaces requires grinding off some of the high spots if possible, filling in the hollows and making a new straight surface for about the last eight feet of the bottom.
   
   If you determine the trailer needs repair or adjustment as well, do it now or your newly straightened boat bottom will soon be crooked again.
5. A dirty bottom has resulted in speed loss or even the inability to get up on plane on many a boat.  Boats left in the water grow weeds and algae and can lose as much as 10 MPH in only one week.  A 200 mile tow on dusty roads, heavily traveled interstate or through a rain storm can leave enough road film on the running surface to scrub off an easy 5 MPH in a free running 70 MPH water craft.

Unusual Noises

If you aware of the sounds normally heard when your boat is running, changes in sound will not only indicate potential problems, but help you diagnose the problem.  Here are a few typical sounds:

    1.  Clatter or Knocking Sound

1. Check the U-joint very carefully.  The needle bearing may be failing, need lube or the shaft splines may be dry.
2. Make sure the bolts tying the U-joint to the flywheel are tight.  Loose bolts allow the U-joint flange to work and can allow the flywheel to spin loose from the crankshaft.
3. Check the tail shaft bearings by reaching in through the inspection hand-hole and feeling for up and down or side to side motion.  There should be no discernible shaft movement.

    2.  Grinding or Rubbing Sound

If you see no visible cause for the grinding or rubbing sound and all the shaft bearings appear to have the correct clearances, it is a good precaution to pull the bowl and impeller.  If a rock or other abrasive object is between the impeller and wear ring or other parts of the jet drive assembly it can cause excessive wear and cut the impeller apart, cut a groove in the bowl or suction piece or destroy the wear ring.

    3.  Squealing or High Pitched Rotating Noise

This type of sound almost always comes just before total failure of the thrust bearing.  Another cause can be an object between the impeller and a non-rotating element of the jet drive.

If you detect this sound, check the bearing housing.  It will get hot if you are about to lose a thrust bearing.

Come home slowly if you must.  Remember, a failed thrust bearing can lock the shaft, let the shaft and impeller assembly spin in an uncontrolled arc.  All of these items will do further mechanical damage and necessitate additional repair expense.

    4.  Hammering or Thudding Sensation

The water hammer or pounding sensation is usually caused by an object which is lodged in the blades of the impeller or between the bowl vanes.

Another cause is intermittent water flow disruption.  A trailing bow rope that has an end whipping just inside the suction piece would be a good example.

A water hammer, if sever enough, for a long enough period of time can break the impeller, cause the bowl to crack or break open and may transfer uneven rotating stress back to the engine crankshaft.

If you experience such a sensation, shut down or go to idle RPM's immediately and determine the cause.  Come home at slow speed if you cannot inspect the impeller or intake area while on the water.

Removal of the foreign object is usually all you will need to do.  There is usually no mechanical damage unless the condition is extreme or you persist in high RPM operation.

Water Leaks

There are only a few areas for water leaks on the jet drive and installation.

    1.  Leakage at the packing gland.

A very slow drip at idle is not bad, if the packing gland is too tight you can burn it so it will not seal.  If the leak is excessive or you suspect an air leak under hard acceleration, tighten the packing gland just enough to eliminate the excess leak (more than 10/20 drops per minute at idle).  If you cannot tighten the packing gland to eliminate the leak or you need excess bolt torque, the packing must be replaced.  Don't panic, it can be done without a jet drive tear down or pulling the engine.  See the overhaul section of this manual.

    2.  Leaks at the Suction Piece Gasket

This can usually be eliminated by re-torquing the bolts.  If you have to replace the gasket, the jet drive will have to be removed from the boat.  See the overhaul section.

    3.  Transom Adapter Seal

1. The transom adapter is sealed to the boat with a gasket.  Apply a new bead of silicone around the joint as a first step or replace the gasket.
2. The seal between the bowl and transom adapter is either silicone, O-ring or both.
   
   You can re-seal this area with more silicone sealer or pull the transom adapter and replace the O-ring.

    4.  Inspection Cap/Extension

Water leakage and air induction are prevented by an O-ring.  Keep the O-ring clean, free of sand and lightly lubricated.  If the O-ring is cut, hardened or no longer an effective seal, replace it.

do not over-tighten the cap bolts.  You can warp the cap and it will not seal.  Make sure the cap wrench is in place so the retainer bolts cannot work loose and allow the cap to be pushed out by water pressure.

    5.  Cooling Water Hose and Cable Thru Hull Seals

These areas and connections should be kept snug to prevent water leakage.  Replace the water hose, cable seals, expansion boots every 3rd year as insurance against failure and a possible flooded boat.