I'm Tristan a French guy living near the lake of Annecy in France and I'm very glad to have found this forum.

I hope I will find some help here because It's been a while I'm trying to fix my boat with only little success...

The boat is a 1979 18ft Ski Nautique equipped with the PCM 351 Ford reverse rotation engine (has 1350 running hours), a velvet drive 1:1 ratio transmission and a 13x13 three blades propeller.

I bought the boat one year ago, it wasn't running on all its cylinders and was popping through the carb. I first cleaned the distributor cap contacts, changed the spark plugs and the fuel filter. The engine seem to run better and on all its cylinders but It was still popping thought the carb at idle in gear and when I would accelerate until 2000 rpm on the water. Then I found that the Pertronix ignition module was malfunctioning (no spark at 3900 rpm on the trailer on the timing light) , so I replaced it with a new one and it allowed the engine to rev until 4600 rpm (on the trailer at least !). At the same time I changed the spark plug wires and the coil (with a Pertronix flame thrower) and did not connect the ignition to the ballast resistor (since it wasn't hooked up either with the previous module). Then I set the timing to 10 BTDC and went on the water but boat could not go past 3600 rpm and 30 mph. I then discovered that the carburetor secondaries were completely stuck closed by corrosion so I cleaned and rebuilt the carb. Back on the water, full throttle only opened the secondaries a quarter so I asked someone to open it manually while I was driving and it didn't change anything, still 3600 max rpm. Then still at WOT on the water I turned the distributor cap on both sides to found the max rpm of the engine while changing the timing, max I could get was 3900 rpm so I set it back to 10 degrees.

I checked the compressions, all cylinders were between 120 and 130 PSI which told me there were no issues with the block and the cylinder heads. Since lag was observed when I would turn the crankshaft by hand and observe the ignition rotor I decided to remove the distribution cover and have a look. The chain was loose on a side so I changed the pinions and the chain with a new kit, aligned the two markings and no more play, it was well tensioned. Back on the water same thing !! It wouldn't go past 3600 rpm !

Then I swapped the carb, no difference.

Swapped the fuel pump, no difference.

Swapped the distributor (with a 1996 Nautique Prestolite electronic ignition distributor on which I installed my reverse rotation pinion), no difference on the max rpm but helped to stick to 650 rpm at idle since the old distributor had loose advance springs.

Removed the valve covers at idle to have a look inside, everything seems to move as it should.

Also, I noticed that the two forward and the two aft spark plugs were white and that the four center plugs were black.

So it cannot accelerate more than 3600 rpm (30 mph) and as soon as the boat tries to pull a skier out of the water the engine pops thought the carb once and then accelerates normally.

Thanks for reading me ! I would be very happy if any of you had some ideas of the reason(s) of my issues !

Have a good week end,

Tristan

3600 rpm and 30 mph don't go together at all with a 13 by 13 prop though. It should go about 1 mph for every 100 rpm with a good 13 by 13 prop.

It seems like you have a problem either with the prop and/or the tach and/or the speedometer 

The little pop on takeoff has a good chance of being the accelerator pump adjustment needing some attention

What's your timing advance at 3600 rpm?

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The prop has some kind of small nicks on the blades outer edges, could it be responsible for the missing 1000 rpm ?

The tachometer appears to be in working condition since it shows 600 rpm at idle (which I can confirm by hearing the engine) and 4600 rpm on the trailer. Off course it might be inaccurate.

Next time on the water I will compare the speedo readings with a gps !

When I reinstalled the carb I left a millimeter gap between the accelerator pump lever and the throttle linkage at idle position. I did so telling myself that with this setting as soon as I would move the throttle forward, fuel would be injected into the intake immediately.

Is that setting correct ?

About the timing advance at 3600 rpm I remember that with the boat in neutral and accelerating manually on the carb to almost 5000 rpm the reading on the harmonic balancer was showing more than 30 degrees.

Maybe next time on the lake I could go full throttle in forward gear (3600 rpm with this engine !!) and try to look at my advance reading.

The engine feels like it is missing half of its power. It doesn't plane out.

Otherwise I'd check the stuff you mentioned next time out.

Nothing stands out as an obvious reason for feeling like it has half of it's power

It may be obvious, but is the flame arrestor on carb intake dirty?

Another easy check is to have a brave person  look down throat of carb while you are maxing RPMs (on water).  If gas isn't getting sucked down the bores, the secondary needle/float could be clogged.

JQ

First of all thank you very much for your help !

Sorry for my late answer, I haven't been able to work on the boat since...

Keno, It is very strange because despite the fact that the engine pops out throught the carb at acceleration, it often pops at start up even with the throttle set to idle...

SNobsessed, I have tried to run the boat on the water at full throttle with the flame arrestor removed and the same symptoms occured... I asked someone to have a look down the carb at full throttle and it appears that fuel is steadily delivered from the four jets located on the top of the carb throat...

67 ski nat, fuel filter and fuel lines are new. I had a vacuum issue on the filter bowl since the clamp retaining the feed line wasn't tight enough. But once tightened to normal, nothing changed...

Jonny Quest, I have adjusted the float level when I overhauled the carb. I set it parallel to the bowl, as it was mentioned per the carb refurb kit I received from nautiqueparts.com if I remember good.

I have removed the antisiphon valve during the on the water tests, nothing improved...

MechGat, I checked that the engine matched the correct firing order when I replaced the spark plug leads and the distributor cap but I will definitely have a second look at it...

uncle-buck, the only gasket I have replaced was the one that seats between the carb and the intake spacer.

Exhaust manifolds and risers (including gaskets) where replaced by new two years ago by the previous owner.

It often pops out throught carb during start up sequence and acceleration (with timing set to 10 BTDC) but still doesn't go past 3600 RPM on gear... 

 Also, I noticed that in gear and at idle it feels like a light clanking noise comes from the lower part of the engine (crankshaft ?) and not from the intake or carb...

I still struggle to find out why the two foremost and the two aft spark plugs are white and dry while the four mid spark plugs are looking black and full of unburned gas...

I consider removing the intake manifold to have a look at the gaskets...

That's why I had the extra magnet and rotor.  After both of these experiences, I decided I needed a bit more confidence when on the water.  So after researching here on the forum and input from some of the senior members I sprung for the D.U.I. Performance distributor and their LiveWire plug wires.  Worth every penny of $600.  Strong and smooth performance. Astounding startup out of the hole.  Most difficult part of the installation was running a 10 gauge purple wire from the ignition to the distributor, but again, worth it!   That's my experience, I hope this along with the suggestions above help you figure it out.  

David 

I will definitely read the thread about carb float adjustment :)

I am considering purchasing a DUI Distributor, in fact this summer the Pertronix EI Ignitor let my down on the water. The boat started fine but after cruising a few minutes at around 3600 RPM, the engine RPM suddenly dropped to around 2400 RPM, back to the harbour I hooked up the timing light and effectively there was no spark beyond 2400 RPM. I then installed a second hand 1996 Prestolite Nautique EI distributor and reached the original 3600 RPM back on the water.

Since I already replaced the Pertronix module when I bought the boat last winter, it is the second time in one year that this part fails.

To me, either the Pertronix modules are unreliable or my electrical system feeding the module is wrong.

The system isn't fed through a ballast resistor, my battery is fine and the alternator produces around 13,5 volts.

I should have determined how much voltage got to the Pertronix ignitor before It failed...

I have another issue now ! While running the boat on the trailer, cylinder number 2 piston bent its intake valve. After opening the right valve cover I discovered that the valve spring retainer broke, allowing the valve to slip down into the cylinder. Water was found in cylinder number 2 and a little in cylinder 3. I removed the right head and found the piston heads in good condition (piston number 2 shows some minor markings only) just like the cylinders bores. The bent valve guide doesn't look cracked so I cannot explain why water was found in the cylinders... Did the head gasket cracked when the piston bent the valve ?

The plan is now to remove the left head, inspect and leak check both heads, replace the bent valve assembly, break-in each valve, replace each valve oil seals and put everything back together.

I wish everybody a Happy New Year :)

Mark