1972 100 h.p. Johnson outboard electrical problems

[Mike Lofgren]

Hi, I have a 1972 100 h.p. Johnon v-4 outboard. For the past several years I have had a recurring problem that I am by now fairly sure is somehow related to the ignition system. At idle or underway at moderate to high speeds and whether at operating temperature or not the motor kicks out for a second or two and then runs fine. It may do this half a dozen times an outing or not at all. I replaced the power pack and coil about ten years ago when I first bought the boat. About five years ago the problem first surfaced. If I open the plug gap a little, it seems to happen more often. Sometimes it won't do it at all and I am sure some adjustment or change I have made has fixed it then it happens again. By the way will this motor have the black wire with the yellow stripe which is a kill switch wire? If not is their some other wire with similar consequences that will let me by-pass most of the electrical system, ignition switch, heat sensor, etc.? Helpful people have suggested water in the gas, prop slippage, etc. but I am sure it is electrical. Which would be more likely to cause the boat to miss like this; the coil or the powerpack or some other part of the ingition? I took the flywheel off and checked all the components under it and they seemed to be fine. I am coming up on six years of pondering this problem and any help that will let me fix it would be appreciated. My wife is starting to think that I can't figure it out and I am beginning to agree with her.<br /><br />MSL

 

[alcan]

Re: 1972 100 h.p. Johnson outboard electrical problems

Hi MSL<br /> This is just a guess. It sounds to me like an air leak in the fuel system. So many times guys replace only the hose end connector, leaving the motor end. Check to see that you have a good proper fit.

 

[Mike Lofgren]

Re: 1972 100 h.p. Johnson outboard electrical problems

Alcan,<br /><br />That is a good thought regards a fuel line leak. I thought about that and you are right I replaced the fuel hose and bulb completely, but didn't check from the motor to the fuel filter, although I did check the fuel filter. The pause in the operation of the engine is so brief, it almost seems like it doesn't happen (no change in the rythem of the motor except at very slow speeds the motor kind of wheezes or seems to gasp briefly then runs fine) except the motor kicks up and then slams back down violently if I am going fast or pulling a skiier. As I recall the fuel hook-up on the motor is a male fitting that the hose end fits over. Any thoughts on how to check it for leaks? Or were you thinking the fuel line from here to the filter or from the filter to the carburetors?<br /><br />Thanks again for the help,<br /><br />Mike

 

[alcan]

Re: 1972 100 h.p. Johnson outboard electrical problems

Hi MSL<br />I was thinking leaking air anywhere in the system. The fuel connector is just the most often at fault and the easiest to check. Remember your looking for an air leak not necessacerly a fuel leak. This may be a loose mounted carb or fuel pump, bad gaskets,hose clamps missing. As I said I'm just guessing here. These are just some things to check out.

 

[Mike Lofgren]

Re: 1972 100 h.p. Johnson outboard electrical problems

Alcan,<br /><br />Thanks again, I will pursue it. Probably not for a couple of months since the boat is in storage for the winter. I have checked out the electrical system pretty thoroughly and can't find any problems with it unless the power pack or coil randomly and very briefly fails to deliver spark and then more or less self corrects itself. If that is what is happening it is very hard to figure out the problem because it completely unpredictable when it is going to happen.<br /><br />Thanks again,<br /><br />MSl

 

[Joe Reeves]

Re: 1972 100 h.p. Johnson outboard electrical problems

MSL.... Your engine DOES NOT have the "Black/Yellow" wire which pertains to the "Magneto Capacitance Discharge" ignition system (1973 up). Your engine has the "Battery Capacitance Discharge" ignition system which depends on a battery.<br /><br />If the problem is a gradual drop in rpms, the cause would be related to fuel. If the problem is a sharp, instant drop in rpms, the cause would be related to ignition.<br /><br />Are you using Champion s/plugs L77JC4 with the gap set to .030? If not, give them a try. There are times when the problem is just that simple.<br /><br />When this problem occurs, is it a case of simply losing rpms... or is it a case where as the engine actually cuts out, such as the sensation of turning the key off and on rappidly?

 

[jhreed]

Re: 1972 100 h.p. Johnson outboard electrical problems

MSL, What you're describing sounds almost like what happens to a reed valve when it gets a tiny bit of crud under one of the blades and upsets the mixture very briefly. Of course, any momentary short in any wire might give the same symptom(s) so this could get quite involved. Try to tie the "miss" with an event like turning, trimming, etc. Good luck... Jim Reed.

 

[Mike Lofgren]

Re: 1972 100 h.p. Johnson outboard electrical problems

Joe Reeves,<br /><br />Hi thanks for your reply. When the motor cuts out(if I am pulling a skiier) it is a sharp instantaneous stoppage of the motor for the briefest interval which causes the motor to kick up and slam back down violently against the transom. When idling underway the motor kind of wheezes and acts like it is going to stop running for a perion of time. Sometimes the motor actually dies and when I restart it it runs fine, in other words the problem doesn't continue after restarting. I have tried the marine plugs which are champion L77V I think which only have the center electrode and then fire to the edge of the plug ( no side electrode ). It does it with these more often than with standard style plugs. If I make the gap say .035 to .040 on a standard plug (just to experiment) then it seems to kick out more often but it is so random, I can't be sure if the plug gap is causing it. I will try the plugs that you recommend and I agree it could be that simple.<br /><br />Jim Reed,<br /><br />Thank you for your reply. For a time it seemed like it happened when the motor was cold or only at the beginning of the day and then also only when pulling a skiier with the boat trimmed out flat with the most drag on the hull. But then sometimes it will do it when I am just leaving the dock under idle. I am sure there is some direct explanation but it is very illusive. <br /><br />Thanks again for all of your helpful suggestions.<br /><br />MSL