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Hi, I have a 13ft fibreglass boat with a 35hp 1977 Johnson on it. It had been sitting for quite a few years until Dad passed away and it was left to me. It starts and idles fine, revs out quite well I think with just earmuffs on it. Problem is, it just doesn't get up and plane when on the water. I remember as a younger guy, I used to ski behind this boat, but now, It wouldn't pull a child on a tube.
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Regardless of the problem, it is wise to first remove both spark plug, then take a compression reading... what is the compression psi of each individual cylinder?
Then, with the s/plugs still removed and using a spark tester whereas you can set a 7/16" air gap... the spark should jump that gap with a strong blue lightning like flame.. a real SNAP!.... Does it?
Do not reply with generalities such as... The compression & spark are okay <-- statements like that mean nothing to us.
Now, if the two tests above check out, the problem you describe is usually a fouled carburetor, clogged, fouled, gummed up, due to sitting for a long period of time. Remove, dismantle, and clean the carburetor, paying particular attention to the brass high speed jet which is located in the bottom center of the float chamber, way in back of the drain screw. Clean that jet carefully with a piece of single strand steel wire as solvent just doesn't do that job properly.
Use a carburetor repair kit, no doubt available on this site.
Make notes, take pictures. That little spring that could go on two ways... you'll remember which way it goes? No you won't!
Adjust the float and the slow speed needle valve as follows:
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(Carburetor Float Setting)
(J. Reeves)
With the carburetor body held upside down, the float being viewed from the side, adjust the float so that the free end of the float (the end opposite the hinge pin) is ever so slightly higher (just ever so slightly off level) than the other end. And when viewed from the end, make sure it is not cocked.
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(Carburetor Adjustment - Single S/S Adjustable Needle Valve)
(J. Reeves)
Initial setting is: Slow speed = seat gently, then open 1-1/2 turns.
Start engine and set the rpms to where it just stays running. In segments of 1/8 turns, start to turn the S/S needle valve in. Wait a few seconds for the engine to respond. As you turn the valve in, the rpms will increase. Lower the rpms again to where the engine will just stay running.
Eventually you'll hit the point where the engine wants to die out or it will spit back (sounds like a mild backfire). At that point, back out the valve 1/4 turn. Within that 1/4 turn, you'll find the smoothest slow speed setting.
Note 1: As a final double check setting of the slow speed valve(s), if the engine has more than one carburetor, do not attempt to gradually adjust all of the valves/carburetors at the same time. Do one at a time until you hit the above response (die out or spit back), then go on to the next valve/carburetor. It may be necessary to back out "all" of the slow speed adjustable needle valves 1/8 turn before doing this final adjustment due to the fact that one of the valves might be initially set ever so slightly lean.
Note 2: If the engine should be a three (3) cylinder engine with three (3) carburetors, start the adjustment sequence with the center carburetor.
When you have finished the above adjustment, you will have no reason to move them again unless the carburetor fouls/gums up from sitting, in which case you would be required to remove, clean, and rebuild the carburetor anyway.
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Thanks for the very detailed reply Joe.
I don't have a compression tester so I'll have to wait until I can borrow one of a mate. Also I've never seen a spark tester as you have described. I've always just held the lead about 1/2 inch away and checked the spark like that. I'll ask around and see what I can rummage up.
I'll post the results as I've had a chance to test the compression and spark.Comment
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Ternjo.... Testing the spark as you describe is okay. You can also slip a #2 philips screwdriver into the s/plug boot then hold the shank that 7/16" or 1/2" away from the block (avoids that startling shock!). Here's something you could throw together in your spare time..................
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(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.
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Thanks Joe, I love the idea of your home made spark tester! I will definitely be making one of those.
I am confident that the motor has good compression, but I will get an accurate reading as soon as I can.Comment
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