1986 Ski Nautique Ford 351 Commander (Misses badly under load, great on trailer)

[RRR]

I'm original owner and love my boat. For almost a year now I've had the boat in and out of (2) boat repair shops trying to solve the engine missing issue when under load. Seems to run fine at high RPM's once the sputtering clears. Sometimes its very difficult to restart after running for a while. Its been extremely expensive up to this point and nothing has been solved.
Items that have been recently replaced:
All fuel filters replaced.
Converted points to electronic ignition.
Installed brand new carb.
Brand new HEI Distributor and plug wires.

The well is running dry so any help would be greatly appreciated.

[Mamigacz]

After replacing the carb did the engine run any different from the original carb?

After switching to electronic ignition did the engine run any different from the points set up? Did you pull the distributor out to do the conversion?

Did you change the coil after the electronic ignition conversion? If so, what coil did you get? Some coils require 12V (no ballast resistor)

Do you have a timing light? If so, what is the initial timing set at?

Have you verified that the plug wires are in the correct order? This can easily be mixed up, especially with a non standard rotation engine.

[surroundsound64]

Mine would do the same thing when running the eliminator electronic conversion kit, but after installing a Davis HEI that went away.

Bad gas?

[RRR]

Thanks for the reply! Nothing has changed in the performance after all the changes.
The coil has yet to be swapped out., it is the original 28 years old.
Come to find out after looking today that the spark plugs appear to have not been pulled and analyzed. I'm not an engine guy but it seems that a tune up would include checking these?? I might attempt this myself after soaking the threads with something to loosen them.
Could a bad alternator cause this?

[RRR]

Thanks for the reply. The distributor is a "Powerfire". The kit used for the point swap out was a "Pertronix" Ingnitor.
I've never emptied the gas tank but put new gas in every time out.

[Mamigacz]

Thanks for the reply! Nothing has changed in the performance after all the changes.
The coil has yet to be swapped out., it is the original 28 years old.
Come to find out after looking today that the spark plugs appear to have not been pulled and analyzed. I'm not an engine guy but it seems that a tune up would include checking these?? I might attempt this myself after soaking the threads with something to loosen them.
Could a bad alternator cause this?

Yes, typically a tune up would include a plug change. However, inspecting plugs is a good indication of other things that are wrong. I would pull them all out and note which ones are wet and black. If you have a digital camera you could send pictures of plugs that look suspicious. Make sure to note what location the suspicious plugs came from.

No, a bad alternator would not give the symptoms you are describing. Especially on a non-fuel injected engine. Is your volt gauge reading 14volts?

If you want I can post some pictures of the correct firing order to make sure the wires are going to the right posts on the distributor cap?

Was there any event, change, or something that happened before it started running funny?

[jhersey29]

The alternator could cause issues. I replaced the points in our 88 nautique and set the timing. It just ran like pooh under load. It wasn't a good boat for skiing the way it ran. I tried different advances on the timing and nothing worked. Put in a new alternator and it was perfect with no issues. I can't remember but I did advance the timing a tiny bit after all said and done. Not sure now with your electronic swap as ours still had points. I replaced the points because we were running the boat had with lots of footing. Took me 3 weeks to get it right again with the alternator swap.

Sent from my RM-877_nam_att_205 using Tapatalk

[RRR]

That would be awesome if you wanted to show me some pics of the wiring. I'm trusting that the shop I have it in now has it right since I have asked them to double check a few times already. I have the RT Rotation setup as labeled on the engine.
Thanks!
As far as an event before it started running funny, it would only run funny after being on the water for a long time. I took it in for a tune-up service and after the mechanic pulling the motor out twice due to him breaking bolts, etc. they finally got it back to me with more issues then where I started, one being that the shifter cable was out of adjustment (had to jiggle shifter to get motor to start) but the current shop has since made it better.
The current shop did all the previously listed installs.
Thanks!

[Mamigacz]

A R.H. rotation 351W should be 1-8-4-5-6-2-7-3. That order should be followed in a counter clockwise rotation measured on the distributor. The cylinder order is:

front of engine

5 1
6 2
7 3
8 4

back engine

If you confirm that the firing order is correct, and there is no suspicious plugs, I would start looking at the coil.

The alternator question came up again from jhersey29. What does your volt gauge read when its running?

[RRR]

Confirmed correct firing order and plugs checked out all ok. Will be taking mechanics on boat test this week to diagnose again.
I'll post as soon as they (if they) find anything.
Thanks All!

[Zach@n3]

Nobody has done a compression or leakdown test yet? Sounds like you have been taking the boat to certified parts swappers instead of actual mechanics.

[s_kelley2000]

I'd be looking at the Petronix Electronic Ignition if it was me. Those Petronix units seem to cause much more trouble then they are worth. We put one on our old 91 Sport and it worked great...for about a month. Then the advance would either get stuck advanced (ran like crap when slowing down/idling and would be hard to start) or it would not advance and it would miss badly and not get over about 15 mph. Summit customer service blamed it on faulty spring and sent us a new set which did not fix the problem. After some arm twisting they got Petronix to send us a replacement unit. This one is still working correctly on my brother's boat but I have heard of way more problems than success stories with these units.

Another common issue when adding an EI is that the coil may not be sending the correct voltage because it is going through a ballast resistor from the factory. If the resistor wasn't bypassed when the EI was installed then it's likely the coil is in the midst of dying a slow death and could be contributing to your problems.

Getting a mechanic with a timing light and a multimeter out on the water would help to diagnose your issues.

[Zach@n3]

Shawn, I thought he said they installed a new DUI unit after that.

[DanielC]

Missing under a load is commonly an ignition problem. At idle, and on a trailer, cylinder pressures are low. When you load an engine, cylinder pressures go up, and it is harder for the spark to jump the gap at the spark plug. The spark energy could be leaking off somewhere else, or simply not there.

[SilentSeven]

....my old Mastercraft (PCM 351) would run like this when the condenser in ignition would fail. Was getting spark across the points and it would misfire badly...barely run. Idled fine.

Sorry, don't know anything about your EI system so can't share more but I agree this sounds very much like an ignition issue. Coil...ballast..points....