1986 Ski backfiring

Can anyone offer any advice?
I am the original owner of an 86 Ski Nautique with a 351w. When I pulled it out of storage last year, I couldn't get it to idle on the trailer.
After numerous checks, I found that the fuel lines had started deteriorating and black rubber ended up in the fuel system all the way into the carb. I had the fuel system replaced, tank cleaned, lines replaced, new separator cartridge, fuel pump and rebuilt carb. Also did a tune-up, electronic ignition upgrade, flamethrower coil, new cap, and plugs. Wires had been replaced the year before with ~40hrs on them. Filled tank with 89 octane and used StarTron ethanol additive. The boat ran perfectly for almost three outings. Was idling back to launch area when the engine shut-down....couldn't get it restarted.
Took boat back to mechanic (he's a muscle car wrench who has very little experience with boats). He began troubleshooting and found two problems, short in ignition switch and burn marks in the cap. Replaced both and got the boat running again but not well. Replaced rebuilt carb with a new 4160. Took to the water and was difficult to start. Once started, as I eased the throttle to higher rpms, it would only achieve a max rpm of 3600 and then began backfiring badly, almost to the point where the engine almost shuts down.

My mechanic's plan is to try these things next:
1. pull and inspect all plugs for possible burns or non burnt plugs and water in cylinder/s from possible exhaust manifold leak.
2. Reverse the set-up on the electronic ignition (heard that works sometimes)
3. Reinstall the points/condenser and coil.

Unfortunately, I cannot get any marine shop to look at the boat due to its age. It has 1650hrs on it without any problems. The boat has not been abused and has been maintained per the specs of PCM's owner's manual.
Any advice would be greatly appreciated!
Thanks!

will do....i'll let you know how it goes...thx!

Sounds like a vacuum leak to me.   Did you replace the base gasket when changing carb?

Lots of guys have had problems with bad carb gaskets.

I have heard you can spray carb cleaner around base of carb to detect leak (it will change RPM if you spray on the leak).

My mechanic recommended installing electronic ignition since the points were corroded when he removed them. If the reinstall of points and condenser work, lesson learned. thx for the guidance. I'll let you know if we have success.

The dizzy and timing has been checked countless times thus far. He even checked the weights and springs in the dizzy and found nothing wrong....weights free of corrosion and springs not broken.   

Just to be clear. You are saying the act of loosening the dizzy hold down bolt (no rotating of the distributor body), will cause the engine to stall?

I would try setting the initial timing while the engine is cranking (not running)

Pull all 7 wires off the spark plugs. (this will keep the engine from starting)
Leave plug wire #1 connected to the 1# spark plug.   
Hook up the timing light (to #1 plug wire)
Make sure the distributor is loose
Have a friend crank the engine over
Time the engine to 8 degree BTDC. while the engine is cranking

After this is done you can move on to troubleshooting other issues.

I just had another thought as to why it stalls when you loosen the bolt. The ignition relies on the distributor being grounded to the block. The condenser and points ground to the dizzy body. Is it possible the ground is lost after removing the bolt? An easy way to prove or disprove this is to run a jumper wire from the dizzy body to a good ground on the engine block.

You might want to have him check to see if the dizzy shaft (at top end) has play. That can make the point gap change.

These weird symptoms of running good and then running poorly could be fuel delivery issue. I'm sure the coast guard wouldn't approve this, but you could run the boat off of gas can of fresh gas

disconnect the fuel line going into the fuel pump
run a new 5 foot fuel hose from the inlet of the fuel pump to the gas can
Run it and see if all your issues go away. If they do, possible problems could be:

water in the gas
water in the filter/water separator
contaminated filter
debri in the gas tank
clogged pick up filter

With all of the ignition work, is it possible you have switched plug wires around? Easy to check.

Once you get the problem solved, strongly suggest to ditch the see thru inline filter & change the fuel line to hard metal tube between FP & carb. This is actually a USCG regulation.

8122pbrainard wrote: WHROSS wrote: we did install an in-line filter between the fuel pump and the carb.    William, What type of filter and how was it plumbed? How about some pictures?

SNobsessed wrote: strongly suggest to ditch the see thru inline filter & change the fuel line to hard metal tube between FP & carb. This is actually a USCG regulation.

William,
As Chris and I suspect, your "mechanic" may be better at making bombs than working on engines. If he did hack the hard line, I suggest finding another mechanic and also not using the boat until a proper repair can be made. Post the pictures.

Glad you got it running.

Gary's Upholstery can match your vinyl if you send them a unfaded tail (from underneath the staple line, for example).   You will still have to find someone to sew it.

If you want finished sewn skins, Christine's is the top supplier. They have CC original patterns.

Just out of curiosity , why is an automotive soft fuel line so dangerous ? I mean , fuel isn't leaking or anything so just curious why this is such a major no no .

I would suspect Jeff that since it's under pressure in a hot enclosed enviroment and easily damaged. What I don't understand is why you cannot use AN lines and fittings. Developed for Army and Navy aircraft if it's good enough for flight you'd think it would be good for boats

Gary S wrote: What I don't understand is why you cannot use AN lines and fittings.

Maybe the AN system isn't the greatest?

Working in the commercial aviation industry I laugh at 99% of the articles written and especially live reports becuase quite frankly they haven't a clue how it actually works. Hollywood movies are my favorite thou. That being said the T-handle that's in the cockpit actually shuts off EVERYTHING!!!!   Those shut off valves are in the pylon (structure hold the engine on the wing) or in the wing root itself. However the main fuel line is probably at least 3" in diameter and running up the side of the engine so there are a few gallons of top grade kerosine sitting there. Could be anything at this point. Fuel is used to cool the oil thru a heat exchanger, fuel is used as hydraulics to open and close some valves and to actuate the varible guidevanes inside the engine to increase engine efficiency. The Feds will find out what happened. They are good at that sorta thing. I'm sure the wrench turners who had worked on that engine are sweating a little bit. Records have already been pulled and they are digging to find out what happenend.