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1971 Johnson won't stay in plane

C

Clint1395

Contributing Member
1971 25 hp evinrude, the motor studders while getting on plane and once there runs good for a couple minutes then dies down back to an idle. It'll stay on plane and run as far as you want at 75% throttle. When it's wide open it will die down after a couple minutes. I'm thinking its a fuel problem. Could it be the fuel pump? Pumping the bulb doesn't seem to help though so I'm confused. Any help would be appreciated. Thanks!
 
I'll try the choke thing tomorrow. It's not getting hot. Just replaced impeller and thermostat. Could this be a coil problem? Maybe one of the coils doesn't work right at high rpms for an extended period of time?
 
kimcrwbr1 said:
Check the wires good for cracks or worn insulation and look close for shorts. Sometimes a wire will ground out at a certain timing position. Have you properly adjusted the engine sync and link? Did you clean the high speed jet? I doubt it is the ignition unless there is a wire shorting. It could be a fuel supply issue you want to get resolved before running it hard. If it is running too lean you can cook the pistons. Did you replace the coils, points, condensers?
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The wires look good, I'll check the wires coming from the coils to see if they're grounding out. If they were grounding out wouldn't it be an instant miss when the throttle plate gets to a certain position instead of it taking a minute or two? I have never had the carb part as I bought the moter from a boat engine mechanic. I have however replaced one of the coils and all points and condensers. When I got the motor it ran pretty good and quickly got worse and worse. I found out that one cylinder had poor spark some swapped the coil with a new one and it ran better. Now I have discovers the new problem. Yes, I set the engine set link IAW the owners manual. Thank you for the help so far!!
 
kimcrwbr1 said:
Have you taken the fuel pump apart? It could be a stiff diaphram be sure and take pics and lay the parts on a bench exactly how you take it apart. The small square fuel pump is especially hard to get right if you dont pay close attention.
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I took it apart this morning. Didn't seem too bad, a little dirty but nothing horrible. Cleaned it and out it back together. Also went ahead and cleaned the carb. I'll take it hunting tomorrow morning and see how it does. It did start and idle a lot easier after I cleaned the carb so maybe it was the carb.
 
I took it out today and it did good at first. Ran wide open all the way to the duck hole (about 20 minutes). When we left it started doing the same thing it was before. Could it be one of the coils? Maybe it's intermiten? Idk, it doesn't really seem like its a fuel problem at this point. I choked it when it was loosing rpms and that didn't help at all.
 
Regardless of the problem, always start with the basic trouble shooting procedure. Without this information, you are simply doing a guess procedure and performing the actions of a parts replacer.

Preferably after the engine is having the problem, warmed up, etc...................

Remove both spark plugs. Check the compression. What is the psi readings of the two individual cylinders?

With the spark plugs still removed, check the spark. Rig a spark tester whereas you can set a 3/8" gap to do a spark test. The spark should jump that 3/8" gap on both cylinders with a strong blue lightning like flame... a real SNAP! Does it?

Please don't come back with a answer giving generalities such as... The spark and compression seems okay or some such reply as that means nothing to us. Many boater do just that and it simply drags the problem out.

The spark plugs should be Champion J6C plugs gaped at .030 .

No spark tester? 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

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 auction at:

http://shop.ebay.com/Joe_OMC32/m.html?_dmd=1&_ipg=50&_sop=12&_rdc=1
 
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