hello, i am working on a 1958 johnson 18hp that i picked up this year. i replaced the coils,points,condensers,wires and plugs. also replaced impeller and rebuilt carb. it ran great in the barrel for 10 minutes then it started coughing(misfiring) ,then stalled and wouldnt restart. still has good spark and plenty of fuel. maybe crap got in to carb?
If using the original pressure tank set up, make sure that system
is working correctly. The tank should pressurize a little after running,
assuming the cap is tight and no other leaks. One can always raise the
tank up higher to see if that helps, then figure out what’s wrong.
Once I had magneto problems with a Mercury. Did the same as you did & it would misfire. Looked at the magneto again & the points turned gold they got so hot.
I found a current reverse from one coil to the other due to a bad bonding wire which the factory never installed. I ran a jumper wire from the magneto plate to the block & fixed the problem. I had cleaned the mating surfaces between the magneto plate & block clean enough to eat off of but the light film of petro gel I used was enough to insulate the two from each other. It was tight enough fit when new to have a good connection but now 40 years later. All the energy from coil 1 was back feeding to coil 2 cooking the points not firing the plug like it should of. Try running a jumper between the magneto plate & the block. My motor ran very well after i installed a bonding wire. Petro Gel is an inert lube I used in many places because it doesn’t dry out.
Pressure tank seems to be working fine. It has pressure and the fuel bowl
On the side of the motor is full and the primer button is hard. I checked spark at both plugs after engine stalled and it looked good. It wouldnt even start with starter fluid.
OK, won’t even pop with starter fluid, sounds like you lost spark… Did you retorque the flywheel properly? If not properly torqued, the key will shear, you will lose spark, and damage the tapered mating surfaces on the crank and flywheel.
Checked spark again. Looks good . I torqued it after replacing everything the other day. I guess i learned that the hard way a long time ago. Checked compression too. 115 psi top cylinder and 110 psi lower cylinder. It just started and coughed and shut off. Im going to clean carb again and see what happens
Took carb apart. Everything looked good. Cleaned it out again and put inline filter just in case. It starts and runs for a few seconds and shuts off will sputter but wont stay running. Have spark on both cylinders.took inspection cover off of flywheel. Everything looks fine. Points are open when visible in the window. Baffled
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