Cub Won't Start

I will try to keep this short as I have tried everything I can think of to get my Cub started after taking it to the Wisc Farm Tech Days. I thought I could get any engine to run, but apparently I have failed on this one. First, at the Farm Tech Days, the last day it rained two inches and the Cub was outside. I had the muffler covered, so no rain in there. I ended up loading it dead on my trailer to get it home. First I thought the magneto was wet, but everything seems dry and if I take out one of the plugs and crank the engine I get good spark (I even checked and adjusted the points). I checked the timing and it sparks at the plug (out of the engine) at TDC (also put my finger over the spark plug hole to make sure I was on the compression stroke as I was hand cranking it to TDC). I checked the wiring to make sure someone didn't mix them up, but that is correct (1-3-4-2). I did a compression check and got about 120+ per cylinder. When I crank it with the starter it does not fire at all. I pulled the plugs and they were wet with fuel (gasoline drips out of the carb after cranking). I even put in new gasoline (purged old gas out of carb by draining and letting some run out to clear the lines) and nothing. Then I took off the air cleaner pipe and sprayed starting fluid in while cranking with the starter and still nothing. I even changed some of the spark plugs with some I knew were good and still absolutely nothing. I took the plugs all out and let them dry off and let the cylinders dry out from the fuel thinking it was maybe really flooded, but still nothing when I put them back (after letting it set for a day). It seems to be an ignition problem, but with spark at the correct timing it would seem to rule that out. Can anyone think of other things to try? Is there anything weard about a magneto that will let it fire at the correct point at very slow speed with the hand crank, but when cranking with the starter it fires at the wrong time (my starter cranks the engine over quite fast) Roger

Yes A fast cranking Mag will spin so fast that the impulse coupling will not engage the housing. this results in way advanced timing, and not enough rotation of the magnet to make good spark at starting, not running speed.
I would try pull starting it if you and the pulling person are solid with the protocol of pull starting a tractor. Do not if at all nervous!
If it runs when pulled, the impulse system in the mag drive might need to be fixed.

If you can hear the mag coupling snapping (as it does when hand cranking) it might be something else.

Heat up the plugs with a propane torch to get them clear of shorting material. put them in warm. It helps a lot. Jim

Just to add to Jim's reply, put a squirt of oil in each cyl before replacing the plugs. Flooding it & using ether will dry the oil out of the cylinders. Not good. If you have an old plug, open the gap to 3/16 & see if it fires when cranking. That should be enough to start it . If it doesn't jump that gap you may have to redo the mag.

Try replacing the condenser. If you can access the magnets touch them with a screwdriver to see if they have strong magnetism. Hal

I had a couple posts in here of same thing. I once got it to start by belting it to another tractor, and it started and ran. Ive since give up and taken it to a machanic. It starts off the starter fine, but he says it wont start off the crank. It cost me $75 to get it running. Had I known of him, he woulda had it 3 weeks earlier. Good money spent at twice the price. Hes going to fix the leaking rear main seal also. Bad wore retainer. Im also going to get him to rebuild the L unit that the belt pulley attaches onto. Ive worked on F-20s and F-30s. Ive worked on my 48 H. But ive had 2 Cubs, and know I cant work on them. In Cool Hand Luke, it was said, A mans gotta know his limitations. Guess im figureing out somma mine. Good luck.

I read in FARM SHOW vol 34 NO 4 2010 page 35 a Mr Peyton says "cabs on Cubs are famous for being unreliable, leaking fuel, and starting hard." He put a carb from Stihl chainsaw on his.
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