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Very low hours 1974 Johnson 40HP will not start

G

Gjkelley31

New member
Hi everyone! Love the forum, been a long time lurker but but I feel I need to post because this motor is driving me insane. I recently purchased a 1974 Johnson 40hp pull start that the owner had in his basement for YEARS. This thing can't have more than 10 hours on it. The guy started it up when I bought it on the first pull. It sat for a few weeks before trying to start it again (when rigging up onto my boat) and now it won't start. I cleaned the carb twice, rebuilt with brand new oem kit. I got it to start a few days ago after trying for a while but it didn't idle for very long. Now it won't do a thing except *occasionally* backfire? Or spit out the back exhaust when I change the idle screw and try pulling again. Has a white spark on both plugs. I'm going to have a heart attack pulling this thing over and over again. Doesn't make any sense why nothing is happening when the motor is basically brand new. Please help. Haven't been on the water at all this summer. Please let me know if you need any additional info or would like pics of any parts. Not sure what to do but it shouldn't start on the first pull.
 
Are u using old tank ,old fuel mixed in with new fuel.40 years plus old,debris from old tank clogging up newly rebuilt carburetor. Fuel lines, primer bulb,fuel tank should be replaced before diving back into carburetor!!
 
johnnygjr said:
Are u using old tank ,old fuel mixed in with new fuel.40 years plus old,debris from old tank clogging up newly rebuilt carburetor. Fuel lines, primer bulb,fuel tank should be replaced before diving back into carburetor!!
Click to expand...

i am not using an old fuel tank. Fresh gas and oil mix. Bulb and tank line are a year old.
 
Have you tried the joe reeves spark test?Piece of wood with finishing nails bent at 90 degree angles to get recommended spark gaps,a lightning blue snap!!
 
Assuming you have compression and spark (Do You?)..... What is your exact starting procedure?

Normal starting procedure = Pump fuel primer bulb up hard... apply a slight bit of throttle... Turn key to START position and hold in key while cranking to activate choke... when engine fires/starts, release key.
 
Put a little dish under the carb and pull the plug on the bottom of the float bowl and see if good fuel comes out possible water in the tank? Pull the high speed jet and see if it has a bunch of crap in there that got stirred up and pumped through the system. You heard it run it probably just needs a good service done to it especially the fuel system. New plugs, points and condensers. Check compression after sitting for long periods it may need a head gasket. The spark should jump a gap of at least 3/8 inch with a crisp blue snap. Put a phillips screwdriver in the plug wire and hold it approx 3/8 from a good ground and have someone pull the rope. It wouldnt be that hard to upgrade to a electric start keep an eye on craigslist for a parts motor.
 
When u say u cleaned carb did u clean low speed jet thoroughly ,soak overnight in solvent, flush with water, dry with dry compressed air
 
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