'72 Johnson 9.5 low speed issues

[scipper77]

I just went through the systems of my new to me 9.5 and got it out for it's first (successful) sea trial.

Top speed on my 12' is 16mph which seems reasonable. At low speed the motor does not feel smooth at all and the behavior seem to be variable. I did not think to pull the engine cover for exhaust leak check but it seemed ti misfire on occasion even at mid throttle speeds.

Here is what I have done since I got it.
-I pulled the wires and cut a little off of the coil ends to ensure a solid connection (coils are updated but not by me).
-I pulled the top half off of the carb and it looked perfect, so I blew air/cleaned what I could and reassembled.
-I replaced the gaskets in the exhaust bypass cover (PITA but it gave me a chance to get the housing clean as a whistle).
-I sanded/polished the points and set the gap.
-I changed the gear lube (there was water but that's another project).
-I have a spark gap checker and it was fine when I checked it, and I can run on either cylinder.
-Compression is #70 on each cylinder.

I'm looking for inspiration as to where to go first so I don't end up making repairs just to see if it makes a difference. My initial thought is that the points may be the culprit. I feel like at WOT they would see more current and at lower speeds they are hit and miss. Also I have not changed the plugs. I ordered new plugs and a new head gasket with the bypass cover parts but I messed up and only got one plug.

 

[Joe Reeves]

Re: '72 Johnson 9.5 low speed issues

Plugs should be Champion J4C or J6C plugs gaped at .030. The J6C may provide somewhat improved performance.

Clean the points with either lacquer thinner or acetone using a small hobby type brush. Make sure the points are set as follows.

(Point Setting Of Magneto Models)
(J. Reeves)

Set the points as follows. Have the flywheel key aligned with the fiber rubbing portion of the ignition points. Adjust the gap so that a .020 gauge will pass thru but a .022 will not. Should there be any question of the points being dirty (touching the contact with your finger would cause them to be dirty), clean them with a small brush and acetone or lacquer thinner.

NOTE 1: Should the operating cam have a small portion on it with the word "SET" imprinted, align this portion with the fiber rubbing portion instead of the flywheel key.

NOTE 2: Should the cam have the word TOP imbossed on the top of it, that is a cam that could be installed upside down and this is simply telling you which side is up. It is not a position where one would set the points.

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Check the spark with the s/plugs removed and use a spark tester available at most auto supply stores, or build the following. Note that testing spark by using the s/plugs is a waste of time. The spark should jump a 1/4" gap on that model with a strong blue lightning like flame... a real SNAP! Does it?
(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

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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.

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.

The brass high speed jet is located way in back of the float chamber drain plug screw/bolt and is screwed in horizontally (1/4x20 thread). Make sure it is absolutely clean. You may need to use a piece of single strand steel wire to clean it as solvent just doesn't do a proper job of it.

The throttle butterfly should just start to open when the scribe mark on the cam is dead centered with the nylon slide that controls the butterfly.

 

[scipper77]

Re: '72 Johnson 9.5 low speed issues

I hooked up my gap tester again and I have a spark that jumps around 1/2" on either plug wire but it is not consistent (looks like it's good at higher rpm's but hard to tell that fast). When I slow it to an idle the spark only hits most of the time sometimes more like half of the time, even at a much smaller gap. What seems odd to me is that if I am checking the spark to one cylinder the miss seems to happen on both cylinders at the same time. What I mean is the motor will stumble on the connected cyl and the plug hooked to the tester will show no spark at the same times. I tried disconnecting the kill switch but that didn't make a difference. Maybe I need to disconnect the kill wires from under the flywheel, or maybe both cylinders missing at the same time is all in my head. I think in my head is possible because based on the number of misses my gap checker shows I wouldn't think I could run the motor on just one cylinder.

It could also be that my gap tester sucks. I'll have to try it on my 5.5 evinrude that runs well.

The other thing I found was a slightly sheared flywheel key. It was sheared all the way at the bottom where the cam that moves the points slides over it so it was only affecting the clocking of the points and barely any of the key was actually sheared. I flipped the key the other way and there is just a touch of play on the cam but the sheared portion was not a factor in that play and the flywheel engages the key well beyond the slightly sheared part.

Should I suspect the kill circuit, gap tester, cam/flywheel timing, points, coils or condenser at this point??

Just about the only things I don't suspect are the carb and the plugs (gap tester indicates a spark issue before the plugs are in the equation).

Seriously I am hoping someone weather amateur or seasoned vet will chime with where they would start because I am getting a little frustrated. I know how to do the work to replace every component in the whole ignition system but that doesn't help me to figure out exactly where my problem lies.