Hi all, need some help!
1971 Johnson 50 hp 2 stroke, 2 Cyl, electric shift. ESL71?
Spark plug L77JC4
History, Dad owned it since new, garage kept, freshwater only. At end of every use, dad tied it to the dock and plulled the gas line ad burned the gas out of the carbs..
This worked great, boat ran reliably until mothballed in about 2005 in garage.
I recieved boat as gift this winter. Before starting it once, I did the following:
Replaced Coils(they were split open)
Replaced water pump & Impeller(ORIGINAL!!!)
Replaced Fuel lines from gas tank to carbs, Replaced filter cover & screen & outer gasket.
Replaced Spark Plugs
Cleaned Fuel tanks/fresh gas/oil (10% methenol)
Changed lower gear oil
When it got warm I test ran motor in yard on hose, it ran great, so I lake tested, it ran great. SO I ran it about 6 weekends just great in the lake, it hit the 27-29 mph it always did on 15 ft tri-hull with "power prop".
About the 7th week, it started to slow/bog down from full speed. I thought it was out of gas so I switched to tank 2, it continued to slow & died. Would not refire, pumping bulb(it was hard) seemed to get engine to fire and die imediately like it was not gettting enough gas..(lower plug was DRY carbony flakey brown, Upper plug was wet brown) Changed plugs, Pumped bulb, rasied "start throttle control to highest possible, it finally started ran rough, I hit gear & gas, as soon as engine got to meduim/high revs it smoothed out and ran full speed to shore..
I took it out of water, dissasembled fuel lines & filter screen, all looked OK, dissasembled fuel pump, diaphrams/gaskets were stretched & stiff, put it all together and it seemed to run.
Took back to lake, same senerio played out and it died, would not restart even with starter fluid it would fire & die like it was not getting gas., had to be towed in.
Once home, I got it to start at high idle but no low idle, so I assumed low speed idle clogged...
I rebuilt fuel pump, lower carb. Engine idles but only seems to run on upper chamber, lower seems to run some but misfire...have good spark, swapped coils, problem stays on lower chamber, so I concluded fuel...Rebuilt cab again, slight improvement(replaced low speed needle valve seats(inner & outer, new float, high speed jet, gaskets.
Finally replaced low speed idle needle valve on lower chamber, mine had wear, like someone took a potato pealer and scooped a concave scoop off the tapered edge...
It runs a little better, (rough idle @ medium speed, won't ilde slow)but seem like lower chamber just not right. I can pull the plug wire on lower chamber and notice a slight change in RPM, but pulling the upper plug wire kills the motor, it will not run lower only...I never touched top carb since it seems to run great on that, there is gas going from upper to lower carb, after all the work, the lower spark plug looks the same as the upper, wet, with brownish tint...other clue is after 15 minutes idling, top plug is HOT to touch, lower plug barely has any heat...switching plugs makes no change..
Have not lake tested again....
I want to be able to troll and slow idle... what's the next step?? The shop??
1971 Johnson 50 hp 2 stroke, 2 Cyl, electric shift. ESL71?
Spark plug L77JC4
History, Dad owned it since new, garage kept, freshwater only. At end of every use, dad tied it to the dock and plulled the gas line ad burned the gas out of the carbs..
This worked great, boat ran reliably until mothballed in about 2005 in garage.
I recieved boat as gift this winter. Before starting it once, I did the following:
Replaced Coils(they were split open)
Replaced water pump & Impeller(ORIGINAL!!!)
Replaced Fuel lines from gas tank to carbs, Replaced filter cover & screen & outer gasket.
Replaced Spark Plugs
Cleaned Fuel tanks/fresh gas/oil (10% methenol)
Changed lower gear oil
When it got warm I test ran motor in yard on hose, it ran great, so I lake tested, it ran great. SO I ran it about 6 weekends just great in the lake, it hit the 27-29 mph it always did on 15 ft tri-hull with "power prop".
About the 7th week, it started to slow/bog down from full speed. I thought it was out of gas so I switched to tank 2, it continued to slow & died. Would not refire, pumping bulb(it was hard) seemed to get engine to fire and die imediately like it was not gettting enough gas..(lower plug was DRY carbony flakey brown, Upper plug was wet brown) Changed plugs, Pumped bulb, rasied "start throttle control to highest possible, it finally started ran rough, I hit gear & gas, as soon as engine got to meduim/high revs it smoothed out and ran full speed to shore..
I took it out of water, dissasembled fuel lines & filter screen, all looked OK, dissasembled fuel pump, diaphrams/gaskets were stretched & stiff, put it all together and it seemed to run.
Took back to lake, same senerio played out and it died, would not restart even with starter fluid it would fire & die like it was not getting gas., had to be towed in.
Once home, I got it to start at high idle but no low idle, so I assumed low speed idle clogged...
I rebuilt fuel pump, lower carb. Engine idles but only seems to run on upper chamber, lower seems to run some but misfire...have good spark, swapped coils, problem stays on lower chamber, so I concluded fuel...Rebuilt cab again, slight improvement(replaced low speed needle valve seats(inner & outer, new float, high speed jet, gaskets.
Finally replaced low speed idle needle valve on lower chamber, mine had wear, like someone took a potato pealer and scooped a concave scoop off the tapered edge...
It runs a little better, (rough idle @ medium speed, won't ilde slow)but seem like lower chamber just not right. I can pull the plug wire on lower chamber and notice a slight change in RPM, but pulling the upper plug wire kills the motor, it will not run lower only...I never touched top carb since it seems to run great on that, there is gas going from upper to lower carb, after all the work, the lower spark plug looks the same as the upper, wet, with brownish tint...other clue is after 15 minutes idling, top plug is HOT to touch, lower plug barely has any heat...switching plugs makes no change..
Have not lake tested again....
I want to be able to troll and slow idle... what's the next step?? The shop??
Last edited: