Spark plug type and gap for 2007 MC 4.3 Alpha

P

Peter Reed

New Member
Feb 13, 2015
22
Plattsburgh, New York
Boat Info
2007 Sea Ray 185 Sport
Engines
4.3L Mercruiser
Last year I purchased a used 2007 185 Sport which has a MC 4.3Alpha engine (serial #1A051257).

When I purchased it, the engine only had 100 hours on it. I did not receive the maintenance records from the previous owner, but he said he had the boat professionally serviced each year. Our family has put an additional 100 hours on it over the past two summers.

I decided to change the spark plugs this year at 200 hours when servicing the boat for winter layup. The boat has run fine with non-ethanol gas, but would occasionally stall while idling.

The MC manual says the following plugs are acceptable for the 4.3 Alpha:

AC – MR43LTS
Champion –RS12YC
NGK – BPR6EFS

Manual also says spark plug gap should be .045 inches.

I purchased six NGK’s (per above) to install in the engine.

I was very much surprised to see that the existing plugs inthe boat were AC – 12607234 (41-993). In addition, the gap on each plug was .055 to .057 inches, not .045 inch as the manual states.

I installed the NGK’s with the gap set at .045 inches. Boat started and ran fine with the new plugs.

Does anyone know why someone would be using the AC –12607234 plugs in the 4.3 Alpha? Also, what impact would these plugs and the .055 inch gap have on performance?

Thanks for your help.
 
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the 41-993's you took out are iridium's. A better plug than what you just put in. As technology progresses, merc supersedes there plug recommendations to keep up with the times. That 993 was the hot ticket a few years back but now merc is recommending a NGK iridium. Give their customer service a call. No doubt any plug will work, the question is how long will it last. On some of these engines, a spark plug change is no joke
 
Thanks. I just found a service bulletin by MC which said the 41-993's were OK for the 4.3, but the gap should have been .045 if used on a carburetor version which mine is. Apparently the .060 gap is to be used on the MPI version.

Any idea how the larger gap would impact performance?

And yes, changing out the plugs is no easy task. Think I'll wait another season before replacing them again!!! :wow:
 
AC Delco says to never regap an iridium plug. I'm sure it could be done.

So you have put a 100 hours on them over a years time. How did it run ? Idle...WOT ?

If it was doing just fine last year and just recently stated to stall at idle , I doubt it was the spark plug gap.
 
It sure looks like the plug can be gapped. My guess is AC Delco worries about the user knocking off the tip of the firing plug. While not sure, I believe the old plugs were installed at the factory with the .060 gap. Interesting that their Service Bulletin says .045 gap for the carburetor version.

The previous plugs ran fine at WOT. Only issue was intermittent stalls when going into neutral. Especially irritating when pulling into docks.

Since they're already installed, I'll try the NGK's for next season and see how they perform. If not as good, it's only another couple hours of knuckle busting to put Iridium versions back in!!! :smt021

Thanks again for your help.
 
I've always used the OEM plug that came in mine - AC – MR43LTS gapped to .045. Never an issue, change every 3rd year.
 
If you have intermittent stalls going into idle check the shift interrupter switch for proper adjustment.
 
Thanks everyone. Would appreciate instructions on how to check the shift interrupter switch. The stalls feel like a fuel starvation issue, but I have the idle fuel control valve and idle adjustment set per factory specs.

I'll switch back to the AC 41-993 on the next plug change, but I still need to check with MC to see if the gap should be .045 for the carburetor version.

I see that NGK has a competitive plug (PTR4G15). Does anyone have experience with the NGK? They are more expensive than the AC Delco, so I am wondering if they are worth it.
 
Mine is a 1999 carbureted 4.3, the sticker on the flame arrestor cover calls for AC-MR43LTS and gap .045. You should have the same sticker on yours. I don't think that spec has changed on carbureted engines.

Regarding the shift interrupt, google it, you will find numerous articles and you tube videos on the subject, best to just watch one https://www.youtube.com/watch?v=kYn7VJ2y7fI. You may need to make an adjustment to the switch or the upper / lower shift cable or both. How is yours behaving? The engine is supposed to stumble when coming from For or Rev to Neutral (that takes pressure off the gears and allows it to shift), but if it is stalling completely the cables need to be adjusted or possibly the lower cable replaced.
 
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