1979 evinrude 70hp, no guts

[GrantAgnelli]

Hi guys, have a 1979 70hp evinrude on my 14ft ski boat, starts and runs like a gem, but won't take off under load properly, takes a long time to wind up if at all, strangely enough goes better with the engine cover off,has 110psi across all 3 cylinders, mixing fuel at 50:1 has rebuilt carbys that are not blocked and are assembled correctly, new pump tank and lines all ok, tested and confirmed good coils/plugs and caps, new cdi module, good earths, water pump ok, reeds are good, no air leaks, new manifold gaskets, prop is a 17 which I am told is the perfect size, and no thermostat, primer bulb always firm, no airated fuel lines, spark is on time at idle advance lever moving,no sticky chokes and all butterfly's operating correctly and still having the same problem... any ideas or has anyone come across this? Im so close to burning it that it's not funny

 

[racerone]

My tester would show 140 psi on a good motor like that.----Flywheel key checked ?-----Bottom crank seal leaking ?------------Did this problem show up suddenly ?

 

[GrantAgnelli]

Ought the motor 12 months ago, first time I've used it

 

[jimmbo]

Why is there no thermostat? Timing at idle is meaningless, is the timing advancing to spec at WOT? Have you done a decarb on it? Are the carbs synced and all opening fully?
Years ago there was a service bulletin about drilling the props for these engines to help holeshot.

 

[racerone]

Perhaps you bought someones problem.----Trouble shooting is required.-------A new head gasket after inspecting cylinder walls is around $ 30.00 here.---Certainly less that what you have spent on parts / effort so far.---Does spark jump a gap of 7/16" on all 3 leads, yes or no ?---And check for a sheared flywheel key too.-And no your timing light won't find that if it is sheared.---Well worth looking by putting # 1 at TDC and seeing where timing mark is.

 

[fireman57]

If it runs better with the cover off you probably have a bad base gasket. Can't burn air with no oxygen left. If it is leaking enough you won't get the power you need.

 

[emdsapmgr]

This powerhead is the early version of the 60-70 hp block. Only 49 cubic inches. Imagine trying to make 70 hp while trying to pull a skier up out of the hole.
These engines were never known a hole-shot blocks. In the early-mid 80's OMC punched these blocks out to 56 cubic inches. Lots more power. An effective way to get more power out of this block is to go down a prop size.

 

[racerone]

The 56 cube blocks were entirely different.----And a 49 cube 3 cylinder should fly on a 14' boat

 

[motoman]

Are you able to trim the motor out any? I have a 1975 70 hp Evinrude on a 16 ft Aluminum Bass Boat that is a absolute beast!!! It will run 36 mph with two people fully loaded . I do have one of the add on tilt and trim units , which helps with the WOT . If you don't have the tilt option play with trim holes om the mountimg plate if everything else looks good .

 

[David Young]

Must be the head gasket, and why no thermostat? My 1977 70 horsepower motor on a 15 foot tri-hull does 35 GPS mph and planes in 4 seconds

 

[boobie]

Try a 15 pitch prop on it and a GOOD de-carb.