Trojan Boat Forum

Has anyone figured out the best spark plugs to use in the old MerCruiser 233 engines. I found two Champions fouled out today and they haven't been in that long.( I might have found my miss at rpm's above 3400.) I changed the fuel filter and found some water so that led to pulling the sending unit in the tank and I found no water. The boat idles smooth as silk with new Bosh platium plugs gapped at .044 but I didn't get a chance to take it out of the marina to open it up. I also put some carb. cleaner thru it and sprayed some around the base and found no leaks. I wonder if it will run now??

Fouled with oil? If so - go 1 temp range hotter and use some

I recommend Champion Marine Stainless Spark Plugs - worth the extra $. Also (as with ANY engine bolt) - put some anti-seize compound on the threads when you install.

The platinum tips plugs last a long time, but don't cary the same current as copper plugs ( I know there wil be many dissenting opinions onthat, but they're are NEVER used in high-performance engines), and can rust in place.

Bottom line - 2 fouled plugs will definietly make the dif! What are your comrpessions by cylinder? I'd watch this - perhaps you havestuck rings, bad valve guides or similar (or just sticky from lack of use). Do you have black smoke? Startup? Idel, Warmed Up? High Speed?

I would really watch that going up a heat range in the plugs, there has been many a burned piston from to hot a plug. How old are the ignition wires? any cracking or sparking to ground around the spark plug boot? Check the compression if its over 100 lbs.of compression it should fire the plug. Each cylinder should have compression within 5% of each other lbs. More even the better. .044 is a wide gap. I know it might be the spec in a perfect world but I would cut the gap to .040. I have a freind that was having plug problems and cut the gap to .040 and the problem went away. NGK are my plugs of choice and they have surpassed any other plug that I have tried. My 360 "s are aproaching 4000 hrs and are still running fine on NGK's. Many Hrs of trolling.

I beg to differ - NGKs have left me dead inthe water many a time in my Yamaha Pro-V 200. The eletcrode breaks internally and they quit. No more NGKs for me.

Yes - using hotter plugs can be dangerous - only go up ONE heat range after (and only after) checking the wires, timing and compression. If the engine is gettign a bit tired and folwoing the plugs with oil - a slightly hotter plugs may help. If you're in a awrm climte - heavier oil (10w040 min - 15W-45 next step) can help, assuming you warm up the engine well before you run it hard.

A yamaha pro v 200 is an outboard and not an inboard they are like comparing apples and oranges. Ignition systems are completely different one burns oil by design and the other one doesn't. What is the recomended oil for that 233. Id bet its a straight weight. And one heat range can make a big difference.

OK....I changed the plugs, fuel filter, put a weighted hose to bottom of tank and pulled about 5 gallon out.....no water, I did find some small rust particles and I gained 100 rpm's ( I'm up to 3500) and it started cutting out again. I installed the electronic conversion kit 2 years ago in the distributor and I'm starting to wonder if the carb. could be stopped up. It idles smooth on start up and I have no black smoke and the timing is dead on.....What now??

No smoke, but your plugs foul sometimes? What doe the plugs look like when they are fouled? Black carbon or what?

What carb? Roch 2-bbl? 4-bbl?

Do you have a fuel-water sep? In-line fuel filter ( to trap rust particle)? A clear-in-line filter is nice so you can see if you have aparticles ollecting, bubbles, etc.

Capt. Ross. The boat has a 2 bbl. Rochester and it does have a water fuel seperating filter on it. The six plugs that were not fouled out looked good, kind of a clean brownish look the other two had a blackish look to them. If I'm correct the #1 cylinder is on the left side of the engine if you was standing in front of the engine. The two fouled plugs are on the right side and I guess they would be 6&8 cylinders. In layman terms it would be the last two plugs on the right side of the engine. I do not have a in-line filter on it ,but may by the time Sat. night gets here, I have a copper line running from the tank to the seperating filter and really don't want to cut it but it would probably be a wise thing to do. I'm open for suggestions!

What was the compression on those 2 cylinders

Bosh platium good for sinkers not any engine I would own . got a ford engine use autolite or motocraft . Gm use A.C. crysler use champ.
over 30 years working on engines I found this is the best bet
Paul

Bosh latinums are not good for heavy loads in a boat! The last forever - whihc is why they're popular for cars, but won't deliver a striong charge when you;re under heavy load.

The Champoin Stainless plugs I mentioned earlier should be available for Fords, and will carry a strong charge and not rust!

This 233 Mercuiser is a Ford V8, right? 351? 1975-1977 engine?
You're correct: Ford V8: From front, counting front-to-back Right=1-2-3-4 and Left:5-6-7-8

By "Fouled Out" you mean the electrode and the tip are shorted? Black sooty substance (carbon)? Are they wet or dry?

If you accelarate hard (ski pullup) - no smoke?

have had nothing but proplems with Bosh platinums in any enging
they carbon foul easly cars trucks or boats people put them in and then they come to to see me to get there engine runing right replace the bosch and there good to go ! ( maybe ok for vw and stuff)