(RE) 15hp johnson running hot thanks for replies

[alan the frogger]

thanks for your quick replies,, i answered what i could in a post,, i`m sorry if that is wrong,I am new to this and this is my first time using it. to state it again,,, 15hp johnson,,1977 model,, i smelled melting rubber before it quit the first time.. it cranks and runs great when first cranked for 20 to 25 minutes,,, then dies... after 30 or so minutes cool down it will crank again,, i`m getting water flow thru the "pisser" but it is hot. I had similar problems once before and changed the powerpack which worked for 3 years. there is discoloration of the paint on the head indicating high heat. is there anyway to check the powerpack? and what else could be checked by a rookie boat mechanic?