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1987 Classic 50, 45HP wet plugs and over heat alarm

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XBRUISER

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Recently Purchased a 18' Lowe Jon with Mercury Classic 50, 45 HP. Sea Trial went well, and after the purchase lost #3 and #4 cylinder ignition. Ended up replacing Stator, Rectifier, and Trigger. Upon inspection they had been replaced with the wrong part numbers, thus leading to the failure. Now the charging system, ignition, is all working well.

The carbs were rebuilt 6 months ago, prior to my purchase of the boat. It has all new fuel lines, Racor filter and separator, new filter under the cowl. Essentially a totally overhauled fuel system.

Now I have two problems.
1. After a solid day on the water, all ran well. The next day, it fell on its face. Pulled the plugs, dried them off, fired back up and ran all day. That night, went back out, fell on its face again, bogged, wouldnt make over 2500 rpm. Pulled the plugs again, #1 was fouled Black. #4 same. Is this a mere adjustment issue(fuel mixture) or possible a stuck needle and seat?

2. With excellent water flow, I get an over heat alarm at 5000-5500 RPM, back off to 4800 and it clears within seconds. Faulty sensor?

The engine was originally a durablend, but it had been removed. I'm running non-ethanol fuel and a ratio of 50:1

Any help would be appreciated.
 
Is engine really running hot? Have you tried infrared heat gun on head? ground sensor wire to block, if alarm sounds wiring is good. Try a cylinder drop test on engine running,pull one plug wire at a time. Also try an open air gap spark test. Test your compression first.
 
Ill try grounding the sensor today. Will take me temp gun with me later today. What Should i be looking for compression wise, numbers?

It is firing on all cylinders, it runs perfect under load, so long as I clean the plugs before the each trip
 
not sure of exact # But they all should be within 10% of each other for compression. sounds like an overrich issue,needle sticking in seat? float adjusted too low?
 
Atarting to think it's electrical. When it sits overnight, it loses spark to 1 and 2 cyl. As it comes up to temp, they come alive, can hear the change in pitch while running it on the hose. Baffled beyond belief.
 
Compression test complete, 130 on all 4, that's good news.

now, where might I find a spark plug reference. It has NGK BUHW-2 in it, and seems to be the common plug for that engine. Mercury marine calls for NGK BUZHW. PERPLEXED
 
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