More 496 Ho Troubles
 

I just can't seem to have a trouble free ride. Prior to a few days ago boat ran just fine. No problems other than a leaky water drain actuator on the inboard side of the port motor which was replaced. Took her out for a run and the port engine was running very rich--couldn't and wouldn't run over 3200 rpm with the port throttle about an inch advanced over the stbd. Transom sooting up. Flowmeters show port consuming about 2 gallons more per hour. Several times the port tach went to 0 RPMS although engine was still running at 3200 and twice the engine momentarily shut off. No alarms sounded during the ride. I changed both the primary and secondary Merc fuel filters and cut them open--nothing. Scanned the engine with Rinda and no faults registered. Took out boost pump and checked the screen--nothing. Pulled vacuum hose off pressure regulator and no gas squirting out. Put fuel pressure gauge on rail , at dock, and at idle and 3000 rpm about 43 lbs on the gauge. Checked all spark plug wires and are connected. Removed flame arrestor and it was clean. Pulled 2 plugs out of each bank and all have black areas on the porclein. Boat obviously running very rich but why and whats the fix--very frustrated?

Is the motor stock ?
Call simmons marine in franklin ohio,
They just repaired mine and it runs perfect.

Engine is bone stock--no modifications....

I just had issue with 1 motor lagging. Ended up being plug wire. I pulled all plugs and read them #4 was slightly different than others. Went out at dark and sprayed all plug wires down w/water and ran motor and you could see bad wire arcing. My wires only have 15hrs on them.

Marcus

replace plugs w/ superceded part number ac 41-932 especially if jap plugs are in there

Just bought the AC plugs last night. Will be installed today. I was told not to gap them at .060 but to leave them as they come out of the box.

What's wrong with Jap plugs?
 

This year I've put the NGK PZTR5A-15 in my 496 HO, which still had the original AC plugs after 200+ hours.
Actually, the engine was still running nicely, and the old plugs were in excellent conditions (I kept them as spare, just in case).
But the new NGK in my experience so far are slightly better.
Instantaneous cold and hot start, engine running as strong as before, if not stronger.
Interested to hear if you have anything negative to report, and if so for which plugs exactly.

PS: in reply to goldeneye - fwiw, I didn't touch the gap of those NGKs, but as it happens it was already .060 out of the box.

You could have knocked me over with a feather !!! It was the plugs--the original Denso brand with not that many hours on them. Plugs appeared to be in good condition, showed running rich and, passed the shake test. Installed AC 41-932 which I believe are really Denso complete with the same Japanese markings. After the plug change, boat ran very well with none of the missing. Also, had an opportunity to try the clyinder drop test on my Rinda software--really Cool...

mapism - had trouble w/ ND plugs only on 496 for some strange reason. plugs always look pretty good when removed. Just wont fire good under compression. replaced w/ ac delco (which has also been superceded). and no more problems. Go figure??

Sorry - Denso plugs suck. NGK no problems and I prefer them over delco, but our parts dept stocks the delcos. So thats what we use