72 johnson 100 hp question

[Monk38]

I have a 72 johnson 100 hp. when I try to start it cold, it is a fight. usually takes 10-15 minutes.... just won't fire.( I try different things for this 10 min choke no choke, disconnect fuel line in case it is flooded ect.) Then it fires up. After it fires up you can immediately shut it off and restart it as many times as you wish. It runs immediately. It runs well wide open and trolls down nice for a whole day of fishing. I am obviously not a boat mechanic, but was wondering if you all had some thoughts on why getting it started is soooo difficult. it isn't much fun at the boat ramp! any thoughts would be appreciated. Mike

 

[david_r]

Re: 72 johnson 100 hp question

i would suspect a fouled carb ,an air leak in the fuel delivery ,misadjusted/faulty choke , or you need to do a link and sync

 

[Joe Reeves]

Re: 72 johnson 100 hp question

(Voltage Drop To Battery Capacitance Discharge)
( Pulsepack When Electric Starter Is Engaged)
(J. Reeves)

On the older Battery Capacitance Discharge ignition systems (1968-1972), the electric starter reaches a point, even with a top notch battery, whereas the starter will draw excess voltage/current/whatever which results in a voltage drop to the pulsepack. The cure is to purchase a diode which is capable of handling 12 volts and installing it between the starter terminal of the starter solenoid (NOT the battery cable terminal) and the wiring terminal that supplies voltage to the pulsepack.

The diode must be installed so that the current flows from the starter terminal of the solenoid to the pulsepack... NOT vice versa. When that diode is installed in this manner, when the key is turned to the start position, the voltage that is applied to the starter is also applied directly to the pulsepack via the diode effectively eliminating the voltage drop and energizing the pulsepack with the required voltage needed for its proper operation.

 

[Monk38]

Re: 72 johnson 100 hp question

thanks, where do I get this diode, what does it look like? would hooking up 2 batteries (12v not 24v) help this problem in the short term? Again any help is appreciated. Mike

 

[Joe Reeves]

Re: 72 johnson 100 hp question

Any diode capable of handling the battery's 12 volts. Should be available at any electronics parts store.

 

[Monk38]

Re: 72 johnson 100 hp question

OK... I bought the diodes both 1amp and 3 amp, Now how do I hook them up... I see the starter solenoid with several wires. I also see the pulse pack. How do I link these with the small diode?? I do have a service manual If this helps explain. Sorry for all the questions, but I really appreciate your patients and experience... Mike

 

[Joe Reeves]

Re: 72 johnson 100 hp question

As per my previous instructions...... "The diode must be installed so that the current flows from the starter terminal of the solenoid to the pulsepack... NOT vice versa. When that diode is installed in this manner, when the key is turned to the start position, the voltage that is applied to the starter is also applied directly to the pulsepack via the diode effectively eliminating the voltage drop and energizing the pulsepack with the required voltage needed for its proper operation."

Connected between the starter terminal of the starter solenoid and the powerpack (pulsepack) wiring terminal....... the pulsepack terminal that registers 12 volts when the key is in the ON position. Usually the purple wire leading to the pulsepack.

 

[Monk38]

Re: 72 johnson 100 hp question

Well,

I did the diode wire.... Not fixed. intermittent spark, sometimes it starts and runs great. other times( Like today) won't start and all and seems to have no spark. Last time I ran it, it started fairly well, but cut out twice on the lake. One time it would restart the other was a long trolling motor ride home! what are my next options. Mike

 

[Monk38]

Re: 72 johnson 100 hp question

Ok, seem to be getting spark.... still no fire??

 

[Monk38]

Re: 72 johnson 100 hp question

have spark now no fuel. It will start immediately if I put a little gas down the carb. dies as soon as it runs out. New fuel pump? where do I get one??