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1981 70 h.p. Evinrude outboard only running at 1/4 power, help!!!

M

MN boater

New member
This boat was purchased two years ago and only runs at about 1/4 power. It is a 1981 outboard Evinrude 70 horse powered motor on a 16 ft sylvan boat. It has been on the water about two dozen times the last 2-3 years and almost always runs at about 1/4 power. Every once in a while the engine will suddenly kick in to full power and run great but it lasts for only about 5 minutes. We just rebuilt the carb's hoping that would do the trick but it didn't help. Also we have put in a new fuel line, spark plugs, fresh gas and replaced the coil assemblies and nothing has helped. Anybody have any advice? We're too broke to drop it off any where and really want to get this baby running well for the summer. Thanks!
 
is your fuel pump working right run hose from pump into clear container and see if your getting a good stream comming out but be very careful not to splash dont want fire
 
Remove the air box cover and take it for a run, put some fuel in a spuirter bottle and squirt fuel done the throats of the carbys one by one. If it takes off when you spuirt fuel down the throat of a carby the problem will be a fuel problem with that carby, if it bogs down and slows then that carby is working. I would check compressions before doing anything
 
Regardless of what problem one might encounter, always start with the basic troubleshooting procedure. Check the compression which should be in the range of 100+ psi (somewhat less on the smaller hp engines) and even on all cylinders.

With the spark plugs removed, rig up some type of spark tester whereas you can set a gap to be jumped. On your engine set the gap to 7/16". The spark should jump the gap with a strong blue lightning like flame..... a real strong blue snap!

(Magneto Capacitance Discharge Coils - Continuity Test))
(J. Reeves)

Check the continuity of the ignition coils. Remove the primary orange wire from whatever it's connected to. It may be connected to a powerpack screw type terminal, a rubber plug connector, or it may simply plug onto a small boss terminal of the coil itself.

Connect the black lead of a ohm meter to the spark plug boot terminal, then with the red ohm meter lead, touch the ground of the coil or the powerhead itself if the coil is still installed.

Then touch (still with the red lead) the orange wire if it's attached to the coil, or if it's not attached, touch the primary stud of the coil. You should get a reading on both touches (contacts). If not, check the spring terminal inside the rubber boots of the spark plug wire. Poor or no continuity of a coil is one reason for s/plug fouling.

Thousands of parts in my remaining stock. Not able to list them all. Let me know what you need and I'll look it up for you. Visit my eBay store at:

http://stores.ebay.com/Evinrude-Johnson-Outboard-Parts-etc?refid=store
 
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Compression is good, coils and spark plug wires have been checked and have good continuity. Is there a chance it could be a timing issue? Thanks!
 
Timing issue? Not likely if the engine suddenly kicks into full power then drops back after 5 minutes...... timing just doesn't do that.

If you can manage to double check the spark after that 5 minute blast, that is the engine is now dropped back to the 1/4 power level. That might tell you something there...... still good spark OR no spark on a cylinder, something of that nature.

If (above) the spark is still good (jumps a 7/16" gap), I'd be looking for a fuel restriction problem or something overlooked within the carburetor(s).

(Fuel Anti Siphon Valve)
(J. Reeves)


Many of the later OMC V/6 engines incorporate a fuel restriction warning via a vacuum device attached to the powerhead. If the engine overheats, or if you have a fuel restriction, the warning is the same.... a steady constant beep.


NOTE... Only the V/6 & V/8 engines have the above "Fuel Restriction Warning". The warning horn will not sound on the other models.

The fact that a engine is not overheating, but the warning horn sounds off with a constant steady beep, and that the rpms drop drastically would indicate that the engine is starving for fuel due to a fuel restriction. Check the built in fuel tank where the rubber fuel line attaches to the tank fitting. That fitting is in all probability a "Anti Siphon" valve which is notorious for sticking in a semi closed position. It will be aluminum, about 2" long, and the insides of it will consist of a spring, a ball, and a ball seat. If this valve exists, remove it, knock out those inner components which will convert it to a straight through fitting, then re-install it. Hopefully that cures the problem.


The above procedure will cure a restriction problem with the anti siphon valve as stated. BUT, it may also allow fuel to drain backwards to the fuel tank when the engine is not running (siphoning backwards) due to the fact that the carburetors/fuel pump etc are higher than the fuel tank. This condition is not an absolute as the valves in the fuel primer bulb usually prevent this backwards siphoning problem. However.... if this does take place, the cure would be to install a new anti siphon valve.
Thousands of parts in my remaining stock. Not able to list them all. Let me know what you need and I'll look it up for you. Visit my eBay store at:

http://stores.ebay.com/Evinrude-Johnson-Outboard-Parts-etc?refid=store
 
I know this sounds simple, but replace the bulb in fuel line, after time internal parts wear and prevents fuel flow. I found this out the expensive way like you are.
 
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