'77 25 HP stalls past 1/2 throttle - Coil Issue or ?

[Notaone]

Trying to restore a '77 Johnson / 25 hp which I bought and then set in the barn for 12 years. Cleaned carb, all new fuel lines, new tank, new plugs, new prop, new water pump. Fuel pump appears to be working fine. Motor cranks, idles and full throttles fine in a barrel. Also works fine in gear while in barrel. However, when I get to the lake and the boat is under load, it works ok through about 1/2 throttle, but when I attempt to accelerate further it will stall unless I throttle back to the 1/2 position. One of the coils has a small crack and the center parts is not thight. Last nignt, I sprayed it with water to check for sparking and did not see any. Pulled plug wires and tested spark and the spark from the other coil appears to be better than that from the cracked coil. Questions:
1. Do you guys think my problem is coil related?
2. If not, what else might be causing these symptoms? I have removed the carb and cleaned 4 times and installed rebuild kit.
3. As there appears to be 3 or more manufacturers of coils for this motor, which ones are considered the best.
4. If the coils is failing under load, should I replace both of them or just the cracked one?
Thanks in advance for any suggestions

 

[Daviet]

Re: '77 25 HP stalls past 1/2 throttle

Re: '77 25 HP stalls past 1/2 throttle

1) If the coil has a crack in it you should replace it, it will fail sooner or latter.
2) Could be the high speed jet is plugged, remove the jet and check it. You could also have a coil breaking down under load.
3) I would stick with the OEM coil, may cost a little more but the quality should be there. I have used aftermarket coils when the OEM coils were not available and have had good luck with them.
4) Just replace the defective coil and see if your problem is cured.
Check your results after repairing one problem at a time so you know what corrected your problem.
If you don't have the OEM manual for your engine you might think about getting one, will be well worth the money.

 

[Notaone]

Re: '77 25 HP stalls past 1/2 throttle - Coil Issue or ?

Thanks for your help. Just pulled the suspected coil and it's cracked worst on the back side and appears that it has overheated. Pulled the 2nd coil and it looks like it has also been too hot. Think I'll replace both.