I have a 1980 johnson 175, after about 30 minutes running will die if you put it in gear and throttle up. I can get it to run in gear if I just put it in gear and do not apply throttle, if I have it in neutral I can give it throttle and it runs ok.
That sound's like a fuel restriction. If you have a built in tank, try a remote tank, or simply squeese the primer bulb. You can't run that 175 for long on just any remote tank. They will not supply enough fuel at full throttle. Use it to trouble shoot only.
I tried the portable tank, and had the same result. I did try and sqeeze the bulb and found it help for just afew seconds. I got to looking and found gas pouring out of bottom carb at the base. I tookit back home and tightened the carb as it was loose. I started the motor while using a muff and it sounds like a new motor. I will try putting it on the water tomorrow and test it out. Hopefully the problem is fixed. Even if not thanks for the advise otherwise I may not have found the gas leak and really blow the engine and every thing else up.
