poor performance, backfire 7.4 merc

[Quint4]

1992 7.4 merc carbed. While winterizing last Fall I noticed an occasional arcing from under the rubberboot on the coil to the positive lead on the coil. I replaced plug wires , dist. cap, & rotor and no more arcing. Motor seemed to run ok in driveway so finished winterizing and put her to bed for Winter. Splash day Sunday....hard start and very poor performance with occasional backfire...damn! I am going back to boat tomorrow and checking to see I did not mix up plug wires (hopefully I did....easy fix)...thoughts....timing...bad coil? I also put on a new fuel pump a week ago before un-winterizing but all seems well with it...no leaks and fuel flowing in to carb.

 

[J Levine]

Been there and done that. After Ron DDS guilted me into changing my perfectly working plug wires (after 6 season of use) I spent a very frustrating night last summer chasing this same arching and back fire issue on one of my 454's. After swapping every component in the ignition system between the two engines with no luck getting the arching to go away I found a loose plug wire. I forgot rule number one of troubleshooting... check the obvious first. Anyway, please check the plug wire boots to make sure they are all firmly seated.

 

[Quint4]

I have no more arcing after new wires. I did check for proper seating and it was good.

 

[Redhook98]

Water in the fuel after being stored all winter? Ethanol fuel is a biatch....

 

[Quint4]

Okay got it running good again here is the scoop. Got to the boat this morning and poured the water fuel separator into a clear glass jar...looked good...did not separate.
Next took a copy of firing order from my merc manual and traced each plug wire and pulled each plug and emery clothed them. Everything checked out, I was hoping for a misplaced wire...no luck. Replaced the coil ( $59...what the hell) did not help...damn.
Okay I'm thinking timing is off or something else worse. I finally give in and have the marina service tech come down to the boat ( first time in ten yrs of boating a mechanic has touched one of my boats).....timing was way off. Set timing and it ran way better but still a stutter around WOT. Ignition sensor he says....okay. New ignition sensor on, reset timing again...running real good !! An interesting side note, while checking the last spark plug i saw and heard an arc around the alternator with a puff of smoke (boat not running)...what the hell? I turned off the battery switch and found a wire from the alternator laying against exhaust manifold. It had burned off some of the insulation and was intermittently arcing....not at all good my friends. I repaired the wire and added some split loom as well as cable tied it out of harms way.....really glad I discovered this!...here is a pic of burnt wire:

 

[Cincy Aquaholic]

Whoa, glad you found out about that wire! I don't think they allow roman candles at the marina. Seriously, good to know its running good again. I wonder if it should be a routine practice to run your motors with the hatch open in the dark once in a great while to look for otherwise undetecable sparks like you were having from your coil to your distributor.

 

[BonBini]

So did the ignition sensor take care of the intermittent backfiring?

How far off was the timing? Was it from normal timing chain wear or was the sensor making it off?

Your boat is a carbed right?

Just curious tonight!

 

[Quint4]

Timing was at 0 degrees...was reset to 8 which got rid of almost all backfire. Ignition sensor eliminated it completely. I may have knocked it off when I spent 30 minutes last fall trying to remove the old rotor button...finally had to cut it off with a dremel. Not sure about the timing chain. Boat is carbed. Cincy, I think your suggestion is not a bad idea.

 

[BonBini]

8* deg was a bunch. Probably didn't take much of a move wrestling one of those rotors off.

Glad she's running all good again.

BTW: You mentioned "carbed" from the git go... Duhh Me!