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Info for problem

woodseyes

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Have 1978, 75 hp evinrude, mod 75843C, serial # J0002114. The problem is have is motor dies when I shift F or R and prop is submerged fully in water, it is like it dies when it is under a load. Runs great on muffs or if prop is only deep enough to move water through water pump, will shift forward or reverse and run full throttle, dip in a little deeper in the water and it bogs and dies. Have checked exhaust for restriction (clear), lower unit oil new, Any Ideas.
Thank You ,
from newbe to sight
Woodseyes
 
Have you owned this engine for some time and it ran normally until....... what? It sat for a lengthy time without being run, some work was done on it and it hasn't run right since... what? The engine is new to you and has never run satisfactory? A little history is needed.

Spark plugs should be Champion QL77JC4 plugs, gaped at either .030 (long life) or .040 (hot spark).

Remove all spark plugs,
Check the compression... what is the psi read of the individual cylinders?

S/Plugs still removed, Do a spark test.... The spark should jump a 7/16" gap with a strong blue lightning like flame, a real SNAP! Does it? NOTE that the gap is important!
 
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Have you owned this engine for some time and it ran normally until....... what? It sat for a lengthy time without being run, some work was done on it and it hasn't run right since... what? The engine is new to you and has never run satisfactory? A little history is needed.

Spark plugs should be Champion QL77JC4 plugs, gaped at either .030 (long life) or .040 (hot spark).

Remove all spark plugs,
Check the compression... what is the psi read of the individual cylinders?

S/Plugs still removed, Do a spark test.... The spark should jump a 7/16" gap with a strong blue lightning like flame, a real SNAP! Does it? NOTE that the gap is important!

Engine is new to me and has never run satisfactory, it ran fair for a while, hit jetty and busted lower unit. replaced, plugs are correct, Have spark tester and compression kit. Spark is good, comp. is (Top 128) - (center 125) - (lower 118)

New shaft came with lower unit, am going to try cleaning carbon clean out and recheck fuel system. noticed I have fuel running out of butterfly throats when I choke it at starting when cold. As stated it runs great on muffs (forward - neutral - reverse) or in tub. As soon as put in gear in lake it dies.
Thank You,
grateful for all help,
woodseyes
 
Spark is good has very little meaning..... The 7/16" gap test is important!

Pick up a adjustable gap spark tester at any auto parts store, or when you have time, build the following.

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

You can use a medium size philips screwdriver (#2 I believe) 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

This can obviously be modified to a 6 or 8 cylinder setup tester.
 
I have seen spark gap testers made from a ford distributor cap. Just drill out the center post and fab a disk up that gives you a gap evenly to the outer posts. The TFI distributor cap has the male type plug wire terminals on the cap you just put the plug wires on and ground the center post.
 
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