1981 Johnson 70 power issues

[jeffntanya]

model j70elcim

when we went to test drive it before buying.. the engine started right up and idle fine. at full throttle in gear the rpms would stay low and barely be moving. the previous owner told us that it had done that a few years before and it was just the carbs that needed cleaning. we noticed fuel leaking out from the intake area. he took the boat the local marine mechanic and he checked compression. it was good. he cleaned the carbs and it was ok ever since. for about 1 week. we ran about 6 tanks of gas through without issue.

2 nights ago we took the boat out and it seemed to be doing the same thing pulling out from the marina and then it picked up and was ok for the night.

last night it did it again and didn't clear up t'ill we shut the eninge off and took the cover off to check everything. no signs of fuel leaking. then started it back up and it was ok for the night.

anyone have ideas on this one? coil issue? spark plugs?

Jeff

 

[jtexas]

Re: 1981 Johnson 70 power issues

couple things to check for:

Make sure the tank vent is clear.
Make sure the timer base is advancing without sticking when you throttle up.
Spark test: spark test tool, couple bucks at auto parts store, set the gap at 1/2", look for a strong blue spark.
Make sure the throttle valves stay parallel and open fully (not beyond) at WOT.

Have you checked the spark plugs? Should be champion QL77JC4 at .030

 

[jeffntanya]

Re: 1981 Johnson 70 power issues

thanks for the response.. actually we picked up new plugs today from local dealer.. he sold us champions.. when we changed them we noticed it had ngk's not sure what part no. the boat seems to run a lot smother and seems to even have more power on take off. my next step now is to put a tach in and see if the prop is letting go to 5500 rpm. it doesn't sound like it revs up that high at full throttle.