1974 115HP Johnson choke ???

[Wishiniwuzfishin]

I have a 1974 115 HP Johnson I recently purchased. Has been hard starting when cold since I bought it. Have only been able to get it to start by squirting gas/oil mixture in plug holes. The choke switch at control box is working and choke appears to be staying fully closed while cranking (have cover and air silencer off so I can see choke plates). I have read of the choke bulletin on here and sometime before I got the motor, someone removed the manual choke linkage from the motor. The lever and decals for the manual choke are still on the motor but there is no linkage at all connected to the lever. However, the wiring is still the original set-up. Whoever removed the manual choke linkage did not change the wiring per the bulletin. My question is ...Should I change the wiring as in the bulletin even though the choke switch I am using appears to be working ok and keeping the choke plates fully closed ? I also loosened one bolt on the choke solenoid bracket and tapped the solenoid down about 1/16th of an inch hoping this would ensure the plates are staying fully closed. It didn't seem to help any.
The battery would always start to run down before the motor would start even using constant full choke unless I took the plugs out and squirted gas in the cylinders. I am now using 2 known good batteries wired parallel so cranking rpm is not an issue, at least going by what I hear and see. I did also notice though, that the spark seemed a little weak when I was doing a spark test. It seemed it could have been bluer and "thicker". Any ideas on a cause of weak spark on all cylinders when I have good cranking speed? Thanks for any feedback.
I was going to take pics of the choke and wiring but it's raining here right now.

 

[ezeke]

Re: 1974 115HP Johnson choke ???

If the choke plates are staying fully closed while you crank the engine for a cold start, that is probably not the problem.

When you choke the carburetors, it forces the vacuum to pull more fuel through the tiny capillaries at the floor of the carburetor throats, enriching the fuel/air mix. If the capillaries are clogged, the process willl not work.

On your carburetors, the idle orifices are located behind the plugs on the sides of the carburetor bodies. After the orifices, the fuel passes through three small openings to the floor of each carburetor throat, just behind the throttle plate. If you remove the plugs, you can spray carb cleaner through the orifice, using the plastic tube that come with the aerosol product. If you do this while looking through the carburetor throats with the choke and throttle plates open, you should be able to see the liquid spray out of all of the openings.

This of course is not a substitute for a proper carburetor rebuild, but may allow you to isolate the problem.

 

[Wishiniwuzfishin]

Re: 1974 115HP Johnson choke ???

Thanks for that tip ezeke. Will try it first chance I get. Any idea on the weak spark? I haven't done a spark test for a long time but I can seem to remember a bluer, thicker spark than what I am getting. Mine seems to be a thin whitish spark, same on all 4 cylinders.

 

[F_R]

Re: 1974 115HP Johnson choke ???

Whichever wiring scheme you choose to use, that is a two-stage choke solenoid.

With the original wiring, a thermal switch energizes the first stage, and the choke switch on the control energizes the second stage.

With the modified wiring, the thremal switch is out of the picture and the choke switch energizes both stages.

So, Bottom line is that BOTH stages have to be energized to hold the doors tightly closed for a cold start.

If you are still using the original wiring, make sure the thermal switch is working. It should close the chokes part way when you turn the ignition key on. Then when you operate the choke switch it should slam them tight shut.

Also check the start throttle position. If it isn't kicking the throttle plates open a bit, it will be hard to start. You ARE using the start/warmup lever, aren't you?

The old school though of a fat blue spark went out the window when CD electronic ignition came on the scene. It isn't fat and blue anymore and doesn't have to be. But it is a much faster spark and higher voltage. But what it should do is be able to jump a 1/2" open air gap with ease. Try getting that with your old blue spark system.

 

[Wishiniwuzfishin]

Re: 1974 115HP Johnson choke ???

Thanks for the info F_R. I just looked again (between raindrops) and the original wiring is still intact at the choke thermo switch. But I can't remember hearing or seeing any movement of the choke plates when turning the key to ON. Unless it was so small I didn't notice. Maybe the thermo switch is bad? I think I will update the wiring as per the bulletin. I've just become a little gun shy about messing with any wiring after reading all the warnings about frying electrical parts etc. I guess if I disconnect the battery and make sure I rewire correctly I don't have anything to worry about right ? Yes, I am using the start/warm-up lever but haven't checked for any throttle plate movement when using it. I'll add that to my checklist. Thanks for the spark info. Apparently my spark is good. The motor does seem to run good on muffs once I get it started. Haven't ventured out on the water with it yet.

 

[ezeke]

Re: 1974 115HP Johnson choke ???

One other thing is that you need to use the warm-up lever on your motor.

Unlike later motors that had QuikStart, your warm-up lever advances the timing while giving a little throttle opening so it is always needed for a cold start.

Watch the advance while you move the warm-up lever to be sure that it is functioning properly.