78 70 hp Evinrude help please

Lakerider

Seaman
Joined
Apr 24, 2011
Messages
69
I need a little help.
My dad has a 70 hp Evinrude that is hard to start and when it starts on muffs it idles. When we try it in the water it dies the instant I put it into gear. We had the fuel pump replaced but it didn't help
I replaced all 3 carbs with different carbs from a motor I have that runs fine just to rule out the carbs being the problem. No change. So I am thinking it is a spark issue Can anyone tell me the correct ohms reading for the coils and maybe what the compression should be.
Thanks in advance for any suggestions anyone might have for me.
Another bit of info. It doesn't seem to rev up like it should when using the high speed idle lever on the controller
Rather slow to respond when it is raised And when it is in the lake the lever must be raised to get it to idle at all
 

Joe Reeves

Supreme Mariner
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Feb 24, 2002
Messages
13,262
Re: 78 70 hp Evinrude help please

Compression should be 100+ psi and fairly even on all cylinders. What readings do you get?

With all s/plugs removed, the spark should jump a 7/16" gap with a strong blue lightning like flame... a real SNAP! Does it?

Note that testing spark by using the s/plugs is a waste of time... the 7/16" gap is important.

Actually the ohm reading of the coils is not important... the continuity is, as follows:

(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.
 

Lakerider

Seaman
Joined
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Messages
69
Re: 78 70 hp Evinrude help please

I have not done any compression test or spark test Aim just getting my info together before I tackle the project. Thank you for all the instruction I will let you know what helps and what I figure out. As soon as I get it e to work on it may be a few days before I get to it.
 

Lakerider

Seaman
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Messages
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Re: 78 70 hp Evinrude help please

One quick question. You say testing spark with a spark plug is a waste. How to I check for spark. Do I stick so,etching into the spark plug boot and then hold that 7/16 of an inch from the block and watch for a spark or what. I have always just watch the spark of the spark plug as the engine is spun over while holding the plug against the engine block.
 

Joe Reeves

Supreme Mariner
Joined
Feb 24, 2002
Messages
13,262
Re: 78 70 hp Evinrude help please

One quick question. You say testing spark with a spark plug is a waste. How to I check for spark.

Using the spark plug..... The weakest ignition system on any engine would result in a spark jumping the plug gap when the plug is out in the open... BUT... when installed, the compression would actually blow out that spark, hence the need for the 7/16" gap for a proper test.

You can insert a #2 Philips screwdriver into the spark plug spring connector that is inside the rubber boot, then hold the shank of it approximately that distance away from the block... OR purchase a adjustable spark tester at a auto parts store... OR if you're handy and have the time, build the following...........

(Spark Tester - Home Made)
(J. Reeves)

You can use a medium size philips screwdriver inserted into the spark plug boot spring connector, then hold the screwdriver shank approximately 7/16" away from the block to check the spark or build the following:

A spark tester can be made with a piece of 1x4 or 1x6, drive a few finishing nails through it, then bend the pointed ends at a right angle. You can then adjust the gap by simply twisting the nail(s). Solder a spark plug wire to one which you can connect to the spark plug boots, and a ground wire of some kind to the other to connect to the powerhead somewhere. Use small alligator clips on the other end of the wires to connect to ground and to the spark plug connector that exists inside of the rubber plug boot.

Using the above, one could easily build a spark tester whereas they could connect 2, 4, 6, or 8 cylinders all at one time. The ground nail being straight up, the others being bent, aimed at the ground nail. A typical 4 cylinder tester follows:


..........X1..........X2

.................X..(grd)

..........X3..........X4
 

Lakerider

Seaman
Joined
Apr 24, 2011
Messages
69
Re: 78 70 hp Evinrude help please

Thanks again. While searching around the forums I found a thread discussing a spark tester that you set the gap on and it sells for a few bucks at parts stores. Thanks for your help I will post what I figure out after I do all the test
 
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