Spark plugs-87 2 barrel 4.3

[mwe-maxxowner]

Hey guys. I gots a question fer ya!

I own a boat with an '87 mercruiser 4.3. 2 barrel carbed version. I picked up some autolite ap25 spark plugs for it. First off, are these suitable? And second, what to gap them at?

Thanks for any advice!

 

[Bt Doctur]

Re: Spark plugs-87 2 barrel 4.3

platinum you really don't need MR43T is all you need. installed in a ford truck they call for .050-.056

 

[CaptainMak]

Re: Spark plugs-87 2 barrel 4.3

Honestly, my first choice would be AC Delco plugs, but Autolite is the second best choice in my opinion.
I believe you have the right plugs. 25's.

Gap should be 0.040".

 

[Bt Doctur]

Re: Spark plugs-87 2 barrel 4.3

manual 7 has MR43T or Champion RV15YC4

 

[achris]

Re: Spark plugs-87 2 barrel 4.3

Better than champion plugs are... anything.

Manual calls for AC Delco MR43T or NGK BR6FS. Correct gap is 35 thou...

 

[dubs283]

Re: Spark plugs-87 2 barrel 4.3

Manual calls for AC Delco MR43T or NGK BR6FS. Correct gap is 35 thou...

best plug selection ive seen in this thread...and the ONLY correct gap spec too

 

[MikDee]

Re: Spark plugs-87 2 barrel 4.3

best plug selection ive seen in this thread...and the ONLY correct gap spec too

AC MR43T is all alloy, it'll never rust, plus if you look at the center electrode closely, it's big! bigger the any others, for a strong, sure spark! That's what I found,,, I even used it in a modified street car, it was the only plug the would not foul out!

 

[dozerII]

Re: Spark plugs-87 2 barrel 4.3

I put Autolite in my 4.3 and had a high speed pop and backfire that drove me nuts, after a carb rebuild, then replacement with out a cure, one of the very smart pros on here told me to put AC MR43t's in it and go have fun, so that's what I did, no more problems.

 

[mwe-maxxowner]

Re: Spark plugs-87 2 barrel 4.3

Thanks guys. I just wanted to get some from Walmart with my employee discount, and a quick Google told me these were right. Perhaps I'll return these and pick up some ac delcos, though.

The boat runs like a top, but doesn't idle well unless it is set to idle too high. Then it won't shift well.

When the idle is slowed down to where it should be, it surges. On the downside of the surge it cuts off often. I'm changing plugs and most likely rebuilding the carb.

 

[MikDee]

Re: Spark plugs-87 2 barrel 4.3

AC-Arthur Champion, the other brother, went off on his own, true story!

 

[Bondo]

Re: Spark plugs-87 2 barrel 4.3

Thanks guys. I just wanted to get some from Walmart with my employee discount, and a quick Google told me these were right. Perhaps I'll return these and pick up some ac delcos, though.

The boat runs like a top, but doesn't idle well unless it is set to idle too high. Then it won't shift well.

When the idle is slowed down to where it should be, it surges. On the downside of the surge it cuts off often. I'm changing plugs and most likely rebuilding the carb.

Ayuh,.... It does sounds like a Fuel Delivery issue,...

 

[CaptainMak]

Re: Spark plugs-87 2 barrel 4.3

Better than champion plugs are... anything.

Manual calls for AC Delco MR43T or NGK BR6FS. Correct gap is 35 thou...

I stand corrected. 1993 and up they went with the .040" gap.

 

[mwe-maxxowner]

Re: Spark plugs-87 2 barrel 4.3

Yeah, I believe it is carb related. At any rate I haven't changes the plugs since I bought it, so it's a good time to do them now.

Based on my symptoms, what else would you check? Once off idle, or with idle set around 1000, she runs like a scalded dog.

 

[CaptainMak]

Re: Spark plugs-87 2 barrel 4.3

The boat runs like a top, but doesn't idle well unless it is set to idle too high. Then it won't shift well.

In my book, that doesn't sound like it "runs like a top".

Plugs, wires, cap/rotor or points, fuel filter (inline or in the carb inlet), carb cleaning. Do you do any annual maintenance to it ?

 

[mwe-maxxowner]

Re: Spark plugs-87 2 barrel 4.3

I've only had it one season, most of which I spent rebuilding the boat. I went through the out drive while I had the boat apart. I haven't done much to the motor. I changed the fuel filter and cleaned out the tank while I had it out. I kept fuel treatment in it and put it up for winter with fuel treatment.

I guess what I meant was it runs out nice and strong if you have the idle high, or once you get off idle. It has a nice strong hole shot, and doesn't stutter or miss a lick all the way up to wot.


This isn't a new problem, though. The issue was there when I bought the boat. Now that the bigger fish are fried, I am gonna try to get this one into the pan. Figured I'd start at plugs and carb rebuilding.

Tinkered with carb adjustment and timing toward the end of last season. We can get a real nice idle around 1000 rpms, but that is too high. Try to set it around 700 and it wants to "surge" .

 

[mwe-maxxowner]

Re: Spark plugs-87 2 barrel 4.3

I did also plan on a cap and rotor, since they aren't big ticket items.

There was a decent amount of crud at thecarb inlet filter when I pulled it. Which I'm sure may point to a carb cleaning even more.

And the general consensus is to return these autolite plugs and replace them with the ac delcos, gapped at .035?

 

[achris]

Re: Spark plugs-87 2 barrel 4.3

...Based on my symptoms, what else would you check? Once off idle, or with idle set around 1000, she runs like a scalded dog.

Sounds like the carb needs a strip and clean.... Once that's done, put a vacuum gauge on and check for valve guide wear...

Chris....

 

[mwe-maxxowner]

Re: Spark plugs-87 2 barrel 4.3

Thank you all. I'll most likely pull the carb and take it somewhere to be rebuilt. That way I won't be wondering if I did it properly.