Logo

Mercury classic fifty 45 hp (1986-1989). Please help if possible

Merc-45-classic

New member
I have recently purchased a merc classic fifty 45 horse power. Bought it and was told it runs good. Started it up hooked to a hose with muffs and runs fine. Idles well and will throttle up in forward and reverse. When I put the boat in the water motor seems very lacking in power. Cannot get close to being on plane ( about 5-8mph) but will still idle fine and shift in and out of gear fine. Redid the timing with a timing light and had it set for 28 degrees at WOT (manual calls for 32 while in the water but subtracted four since I did the timing out of the water with no load). Nothing changed after resetting the timing. Have not pulled the carbs apart yet. Cleaned the fuel filter and still have the same problem. Going to take the carbs and fuel pumps apart next weekend ( they are combined on this motor…. One pump on each of the two carbs). Just looking to see if anyone has any ideas on what the issue could be. I also was able to rev the engine up in neutral while hooked to the muffs and ran great. When the boat was in the water, I did the same thing and the motor wanted to bog down and die out? Not sure if that has something to do with the back pressure from the exhaust when underwater or if that has something to do with part of the reason it won’t run like it’s supposed t
 
Fact-----They all sound good and bark / roar on a hose.----It means nothing.----Post your compression numbers.----Check for strong spark on each lead.----Check for blockage in the exhaust tuner.-----Replace water pump impeller.----Test overheat horn.
 
Fact-----They all sound good and bark / roar on a hose.----It means nothing.----Post your compression numbers.----Check for strong spark on each lead.----Check for blockage in the exhaust tuner.-----Replace water pump impeller.----Test overheat horn.


thanks for the response racerone.
the compression on each cylinder was right around 125 for each one, varying a couple digits. Strong spark in each plug. Already replaced water impeller as well as all lower unit seals. I’m not sure what the exhaust tuner is but it sounds like that might be helpful. Any advice on how to access that or the overheat horn? Not familiar with those two things but willing to check if explained how to.
 
Are both carburetors opening up ?------Boost venturi in place.----If it has a flywheel key you should check it.-----Water in fuel ??-----If this motor sat for a long time with fuel in the carburetors they could be gummed up.------
 
Are both carburetors opening up ?------Boost venturi in place.----If it has a flywheel key you should check it.-----Water in fuel ??-----If this motor sat for a long time with fuel in the carburetors they could be gummed up.------


from what I could tell the butterflies on the carbs were opening up but will check next weekend. Going to pull the carbs apart to make sure they are not gummed up as they sat all winter. What is the exhaust tuner talked about previously?
 
Exhaust tuner is between the powerhead and the lower unit.-----They can plug with carbon.----Motor then can not breathe.----Remove lower unit and shine a flashlight up there.----Did one a few years back.----Shop had installed new ignition parts to no avail.
 
Exhaust tuner is between the powerhead and the lower unit.-----They can plug with carbon.----Motor then can not breathe.----Remove lower unit and shine a flashlight up there.----Did one a few years back.----Shop had installed new ignition parts to no avail.


okay thanks, I’ll take a look at it next weekend and post any updates
 
okay thanks, I’ll take a look at it next weekend and post any updates

Just wondering if you found the problem yet? If not I would check the switch box. I bought my Classic Fifty new and still use it. A few years after I had it the switch box went out and acted exactly how you're describing.
 
Back
Top