I recently purchased and older 1981 Johnson 70 hp J70ELCIM that has no power under load, although this problem comes and goes. The carbs are new, as well as the fuel lines. Checked the jets and they look new and don't seem to have any sign of blockage. I have fouled out 2 sets of plugs since running the engine, only about an hour of run time total. Basically the motor seems to run OK until it is fully warmed up (after about a couple of minutes at WOT ) then the no power under load will start. Compression on the motor is good, at 140 psi per cylinder. Visually the motor looks to be in very good condition, but since the motor was installed on the boat, there has not been a link n sync done on it. I know from reading the forums that the butterflies should all be closed at idle, and that the idle rpm is controlled by the advance arm linkage that has the large idle screw on it.
There is a slight gap between the roller and the cam at idle as well, and the advance is coming in slightly before the throttle cam starts to move. Does anyone have any suggestions other than the link n sync to check. Toddo1 (or anyone else) do you still have the instructions in PDF form that you could send to me? Trying to save some money and not buy a service manual just yet.
Scott
There is a slight gap between the roller and the cam at idle as well, and the advance is coming in slightly before the throttle cam starts to move. Does anyone have any suggestions other than the link n sync to check. Toddo1 (or anyone else) do you still have the instructions in PDF form that you could send to me? Trying to save some money and not buy a service manual just yet.
Scott