70hp Johnson, stalls on acceleration

[Clint F.]

Hi...My '77 Johnson 70hp is stalling when I attempt to accelerate from idle.<br /><br />The motor starts and idles fine, even in gear.<br /><br />I have replaced the fuel pump, fuel lines, tank to motor line & bulb, new plugs, tried different gas tanks, had the carbs re-built and sync'd.<br /><br />Please, any thoughts?

 

[DJ]

Re: 70hp Johnson, stalls on acceleration

This is a very common issue, that appears here, with 3 cylinder "loopers".<br /><br />Typically it turns out that one cylinder is not pulling it's weight, due to either spark or fuel.<br /><br />The best way to test spark is to attach an inductive timing light on each plug wire and run the engine under load. Running it in the driveway, on the muffs, will not suffice for this.

 

[Clint F.]

Re: 70hp Johnson, stalls on acceleration

Thanks for the advice, DJ...I'll try tht this weekend. If lack of spark was the case, would the plug reflect this? All plugs are uniform and dry.

 

[Clint F.]

Re: 70hp Johnson, stalls on acceleration

Would one cylinder failing actually cause the motor to stop running? It does not sputter or anything...it's like turning off a switch.

 

[DJ]

Re: 70hp Johnson, stalls on acceleration

They will die pretty quickly. However, make sure you look for any interference with wires both under the hood and in the control box.<br /><br />Also, do this: With the engine OFF and in forward gear (spin the prop by hand while shifting in). Watch the timing plate under the flywheel as you advance the throttle. It should advance smoothly and then stop just before you reach wide open throttle.

 

[Clint F.]

Re: 70hp Johnson, stalls on acceleration

The timing plate is hitting the bumper exactly when the throttle plates are hitting the stops, as according to Seloc...should full advance be reached BEFORE wide-open?

 

[16Pilot]

Re: 70hp Johnson, stalls on acceleration

Quick question guys. Can the spark be affected whether or not it is under a load. What I am asking is if you get spark at Idle why wouldn't you at full throttle. Just curious !

 

[Clint F.]

Re: 70hp Johnson, stalls on acceleration

My impression is that spark can be affected by RPM's...at least on small outboards. It probably applies to larger ones as well.<br /><br />Does anyone know how to adjust the idle timing? The bumper adjusts high-speed, but Seloc is a bit vague on the low-speed.

 

[ddswulf]

Re: 70hp Johnson, stalls on acceleration

i also have a 1977 johnson 70 with what seems to be the same problem. i have also cleaned carbs, changed plugs and new fuel lines and connections. if i test with light under load, and it shows not enough fire, what then? how do you test the coil?

 

[Clint F.]

Re: 70hp Johnson, stalls on acceleration

Swap coils between cylinders and see if the weak spark follows.