mercury 50 bogging down

[killertrance]

hi,can anyone shed some light on my problem.the engine is a 73 ish mercury 50,4 cylinder with thunderbolt ignition.the engine will start,run,rev up,tickover perfectly.put it in the water and go to set off and it just crawls along.as i increase the throttle it just makes an induction noise,no power at all.ive done a drop test,all fine,checked spark,all fine,checked timing,all fine,cleaned carbs,done compression test,120 ish in all cylinders.im at a loss,can any one help.....PLEASE.many thanx,regards,jeff.....ps this engine only has a charging stator that goes to the battery,im not to sure how thunderbolt ignition worx but it has a box at the front of the engine that goes straight to the distributor.so its not the stator.<i dont think????>

[MercMan69]

Killer...
I have an older merc 65 horse that is doing what sounds like the same thing. Does your engine rev when its out of the water, with muffs? My engine is also not charging the battery, is that a clue?

[Frosty]

Killer--still messing down Stanah.

I have seen this before --the 3 cylinders were worse.

Petrol oil -- correct mix and fresh fuel

Try it again only have someone pump the bulb at the same time. Check that there is nothing missing from the airbox. An engine this old can have bits thrown away by people that know better. air strainers etc etc

If still no good try with the cowling off and restrict air flow SLIGHTLY with your hand.

If there is mixture contols on the carbs try 1/2 turn out or 1/2 turn in.

Get a book.

Have you checked the timing to throttle, never mind max advance. With no book I am guessing too. I would try more advance to throttle movement.

This stuff is best in a tank. Whats a "drop test" dont like the sound of that.

[Bergalia]

Ignition advanced too far by the sound of it...:(

[cougarman]

HI guys, Have you tryed a crankcase leak down pressure and vacume test? you might have some crankshaft seals leaking? With no load it seems to run good, but with a load no power? sounds like seals, Note if it is seals you dont want to run it to long you might burn down a cyl, lets hope that dont happen. good luck

[dewey26]

Hey killertrance looks like we are having about the same problem. I'll let you know what I find if I figure it out. If you have time check out my post. May 30th 40HP Mariner too lean? Thanks man.

[markg612]

Killer...
My engine is also not charging the battery, is that a clue?

If it runs with no charge, it has a "rectifier" (small black box near the front of the engine) typical failure otherwise there is no regulator charges by "wild" process, i.e., when the batteries full it's done.

[stonebreaker]

Might check the fuel filter. My dad had a bass boat with an 85 mercury outboard that used portable 5 gallon fuel tanks. Every time we forgot to loosen the vent screw on the fuel tank cap after switching tanks, the engine would run fine until it sucked enough fuel to create a vacuum in the tank; then it would start bogging down from fuel starvation.