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1978 Johnson 25e78c - rough and irregular spark

W

wwager

New member
Motor starts okay, idles rough and when put into gear sometimes runs fine and other times cuts to one cylinder. I put in new plugs and then took them out to see if they were burning clean. The bottom cylinder was clean but the top cylinder looks fouled after a short time at idle.
photo of spark plugs
https://flic.kr/p/2rstZ7T
What might be causing this?
 
Classic " lean sneeze "----Throttle plate opening too early.----Or lean on low speed mixture screw.----Check / replace fuel pump diaphragm.
 
Where is the adjustment for the throttle plate? I checked the fuel pump diaphragm and didn’t see anything like a crack or hole but I will order a replacement. Adjusting the idle jet screw toward more rich doesn’t smooth it out. More recent symptom is when the ignition switch is turned off it diesels and keeps running.
 
wwager said:
Where is the adjustment for the throttle plate? I checked the fuel pump diaphragm and didn’t see anything like a crack or hole but I will order a replacement. Adjusting the idle jet screw toward more rich doesn’t smooth it out. More recent symptom is when the ignition switch is turned off it diesels and keeps running.
Click to expand...
Part #
IMG_8995.png
84
 
wwager said:
Where is the adjustment for the throttle plate? I checked the fuel pump diaphragm and didn’t see anything like a crack or hole but I will order a replacement. Adjusting the idle jet screw toward more rich doesn’t smooth it out. More recent symptom is when the ignition switch is turned off it diesels and keeps running.
Click to expand...
Mine keeps running sometimes too. Not sure if it’s a ground issue or what it is. You probably know how it works but when you turn off the key it is supposed to ground the power pack and kill it. A new key switch fixed it for a while but it’s doing it again.
 
WW---Stop motor.----Put throttle at slowest idle.----Post picture of the stop adjustment on that thin rod that goes to the carburetor.-----Right on the port side of the motor.----At the top of the " towershaft "
 
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