Johnson 70 SLOW?

A friend and I have a new-to-us bass tracker with a 1990 Johnson 70 on it. We finally got it in the water and it idled rough and after a short time of low-to-mid-range RPM running, suddenly lost power. We idled back to the dock. Replaced plugs, found that the cup around the impeller was installed wrong. We also have replaced the thermostat. New plugs and correct installation of the impeller and took it out again tonight. Ran MUCH better (like a completely different motor), but after about 5 to 7 minutes of running pretty hard it shut down on us again. Perhaps shut down isn't the word, but it severely loses power. We have not attempted to get it back into power after this happens in fear of damaging the motor.

Tell-tale is shooting out water good, but there appears to be water coming from the two (exhaust?) ports towards the top center and we appear to maybe have some steam coming from somewhere? i assume its steam as it doesn't seem to linger and disappears not leaving a cloud behind the boat. Tell-tale temp is just slightly warm to the touch and flowing very good. Compression is 115, 120, 120 on the motor as well.

I have noticed to that after idling and turning motor off for a few minutes, we need to hit the primer bulb about 10 times and it will start right back up. We had an issue with the vent on the tank and have unhooked it so thinking it has no back pressure on the fuel, but figured I'd toss it out as possible info that may mean something as well

Have a temp gauge but so far have not had any luck in making it work, nor does the alarm system work currently (in the process of fixing). I'll be getting a basic IR thermometer tomorrow to check temps but just curious of some things we need to look into based on what I've written above.

Re: Johnson 70 SLOW?

take plugs when you in the water after its starts giving trouble turn key & see if any water comes out , if no water . do spark test , clean carbs , make sure no air leaks in fuel system do timing & synchronization .good luck

Re: Johnson 70 SLOW?

durban said:

take plugs when you in the water after its starts giving trouble turn key & see if any water comes out , if no water . do spark test , clean carbs , make sure no air leaks in fuel system do timing & synchronization .good luck

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Thanks, will give it a try. My big concern is the water coming out of exhaust ports, at least I am under the impression that's what the two ports in the upper middle section of the motor are. Should we have water coming out of there at all?

Re: Johnson 70 SLOW?

You should. Thats where most of the cooling water comes out. The tell tale is just a little bit to let you know the pump is working.