1975 85hp Johnson overheating and shift problems

I took my boat onto the lake for the first time yesterday. When I started the motor I
checked to make sure that water was coming out of the engine. At idle it looks to be about a handful of water every 3-4 seconds. I ran the boat full speed (40mph) for about 15 mins and the over heating alarm sounded. So we let it cool off and made our way slowly back to the ramp. It seems as.if the water stream picks up at about 1500 rpms but decreases when RPMs go higher than that. I just installed a new impellar on the motor a month ago.

Also I am having trouble getting the motor into.forward drive. When I move the control forward the engine throttles up before the gears engage the prop. Reverse works flawlessly and I replaced the shift cable last week.

Can anyone point me in the right direction of what to check next?

Re: 1975 85hp Johnson overheating and shift problems

check your t-stat. It may not work properly anymore. Your shift cable is not adjusted properly, that is why it is throttling the engine too much before getting into gear.

Re: 1975 85hp Johnson overheating and shift problems

The thermostat controls powerhead temps when the engine is idling or just above idle. Once the boat gets on plane, the pressure relief vavle opens in the thermostat housing, flooding the powerhead with extra cooling water. If it functions normally, you should not get an overheat when the boat is on plane. When you get into that housing to replace the vernatherm, you should check the nylon valves. Be sure they are not heat-deformed and in need of replacement. Disconnect the shift cable at the engine end. Start the engine and shift by hand. If it shifts normally by hand, then it's a cable adjustment problem. Turn the cable thumbwheel to adjust it.