2 hp johnson, starts fine runs for 20 minutes then dies

This is a 1974 2 hp johnson. I have checked spark, fuel and carb. settings all seem OK. Initially starts right up
then after about 20 min. dies. Will not re-start. Upon pulling start rope I get "ba ba ba ba sound
as though it wants to go. Block does not seem excessively hot, but; something tells me this
is associated with my problem. Something I can't get out of my head is that the "block to lower
unit" gasket comes with only a Very small hole in it for the cooling water to pass through into the
block. Maybe my immigration, but; I think I seem to recall that this gasket bought years ago had a opening the size of the
chamber into which the copper water tube fits, allowing far more water flow into the block, but; this could be one of those senior moments. Anyone have any thoughts. thanks, Rich

Re: 2 hp johnson, starts fine runs for 20 minutes then dies

does the motor have a pee hole? does it feel tight after it stalls? odd smells from the block? if not id look at the filter thats inside the tank, they are notorious for getting gummed up .

Re: 2 hp johnson, starts fine runs for 20 minutes then dies

If your waterpump/cooling circuit is in fact functioning as it should, and she is not overheating, maybe a coil is heating up after 20mins and failing.

I would verify head temp with an infrared thermometer to see how hot she really is. If all is well, use an inductive timing light on the plug wires to see if a coil is failing when warm.

Re: 2 hp johnson, starts fine runs for 20 minutes then dies

These engines should NOT be run with a 1:50 mix. The damn things still have bushings and not bearings. Try to run it with a 1:24 mix or at most a 1:32 with a good marine 2 stroke oil.
These early 1970s little 2 strokes still use 1950s technology and too lean a mix will do a lot of damage.

Re: 2 hp johnson, starts fine runs for 20 minutes then dies

I agree with rolmops.

I had a 1975 Evinrude 2HP that required 24:1 if I ran it longer than a few minutes. I also had to replace the impeller right after I got it. When water is flowing adequately it sprayed through exhaust holes in the back of the leg; no spray there, no cooling.