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71 Johnson 100 HP stalling after hard running

7

70wellcraft

Member
My 71 Johnson 100 HP wants to stall and starts hard after running hard tubing the kids around for about 20 mins. It will usually start with the start lever (spark advance lever) in the up position but when I put it down and then engage the prop and throttle up, it dies. I can usually get it to work if I really throttle up quick and then it sounds like the engine is only firing on 2 of the 4 cyclinders for a short time and then all of a sudden they all start firing and it takes off like a shot. It seems to be plugs fouling to me. I have rebuilt the carbs last year and there is only idle mixture needles on it and no high speed mixture adjust. After the engine is left to cool down a bit, it starts up normally and runs good until after another 20 mins or so of beating and it starts doing the same thing again. I also replaced the plugs early last year. Any ideas?
Thanks
 
Well I am still dealing with this problem. I have swapped out the MSD spark box and the coil and changed plugs and it still does the same thing, runs for 10 mins until really warms up and then its sparking on maybe 2 of 4 cylinders. I am starting to wonder if there is some issue that has occured to the ignition system due to the MSD conversion. possibly points fouling or condenser? I think this engine has 2 or 3 sets of points.
Any thoughts?
 
You should start with a compression test------------If that is good , then remove flywheel---------Remove distributor cap ----------Clean the 2 sets of points and gap to 0.010"--------------Clean distributor cap-------Likely need to replace the anti-reversing spring as well.------------I assume you are not using the original amplifier.---------------Thermostat ( vernatherm ) is installed and working properly.
 
What is the anti-reversing spring? I think I removed the thermostat from the cooling system a few years ago and left it out. I am not using orig amp, I converted to MSD box.
 
As the name suggests the spring keeps the engine from running backwards.--------------If it is badly worn then dust may get on the distributor cap / rotor.-------------Or pieces may be in there loose.-------------------There is no reason to run without thermostat, and that may lead to fouled plugs.
 
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