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Mercury 500 Thunderbolt bogging / stalling

BennesV

New member
I have a 1970's 50HP Mercury Thunderbolt on my boat recently purchased, old engine but only done just over 350hrs and had regular services, first time in the water starts first time every time, idles fine etc, when putting into gear its going fine just above idle as soon as I open the throttle the engine stalls, if I pull the throttle back to idle or neutral before the engine dies it goes back to idle normally, since then had new plugs, carbs cleaned and overhauled, fuel lines changed, compression checked etc. back in the water same thing can cruise at low speed for hours no issue, just when I accelerate it looses revs and wants to cut out, if I don't pull throttle back engine dies out completely and will start after that straight away no issues, it does sound like when I'm trying to accelerate as if there's like a more noticeable rattle / metal noise from the engine (almost like a car with noisy tappets/lifters) I'm out of options and don't know what to do, I'm relatively new to boating and need help
** NOTES **
1. When the boat had new paint done the throttle control was removed opened, cleaned and refitted - but had the same issue before this was done.
2. The propeller does have a small chip out of one of the blades
3. I've used fuel that's a couple weeks old, after carb clean was new fuel (50:1 Mixture ratio)

Any help would be appreciated

Thanks
 
Racer, does this motor have a trigger...?..maybe a wire is bad and when throttle is advanced, it moves wire and disrupts spark.
 
Did anyone replace the fuel pump diaphragm in all this time? Try pumping the bulb while accelerating if motor if it works it's fuel related if not.......
..this motor should have the Lightning Energizer (but after helping another guy with a 50 that didn't I'm not so sure), anyway the energizer has 2 coils 1 for hi-speed and 1 for lo (see diagram)lightning-energizerS.jpg.
 
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I really appreciate the information, Quicksilver. It appears the timing is regulated by a unit that causes wires to move.....these years had poor wiring, don't know what kind of crap they used for wire jackets but it became brittle, then cracked, allowing moisture and resulting oxidation to the copper core itself. I have noticed that some components utilized aluminized wires too....this only adds brittleness to the conductor as well.
 
The wire they used was stranded copper covered with rubber which was common for electrical usage even up 'til a few years ago; I have some wiring harnesses that are good and some that are bad and some with good and bad wires in the same bundle.
 
Noticed that to. Got a couple 402's here. Both spent half time hanging on boat at dock, and winter's in a shed. One has nice wiring, the other is all rotten?????
 
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