Hard starting Cub

Charlie M

Well-known Member
My 47 Cub has been really hard to start most of this summer. Its 12 volts with a J4 mag so cranking is no problem. Tractor acts like it want to start and fires occasionally and if I crank it long enough it
will eventually start and run fine. Sometimes I can't get it to start until trying again the next day. I'm trying to figure out if I have a weak spark or a gas problem. No problem getting gas to the carb.
Everything is tight on the carb and manifold gaskets. When I got the tractor a few years ago it had low compression so had the valves done and shop went through the entire motor checking specs. That was a
about 4 years ago and motor doesn't have a lot of hours on it. When I got it there was a real cobble job of wiring and the tractor had been set up for an external coil and had a condenser attached outside the
mag so I replace the mag coil, points and condenser and went to a single wire alternator. I also replaced the carb as original had a lot of physical damage. Carb is IHC carb. Tractor started and ran great
after that and runs great now if I can get is started. I did try a different condenser I had in the drawer (previously used) and thought it helped but a few days later nothing had changed - still hard to
start. I was finding oil inside the cover where the points are and in the cap so I changed the oil seal at the front where the mag attaches and cleaned all the oil from the points area and made sure points
were clean. I hear the impulse coupling working. I'm looking for what else to look for. Mag is back together correctly as eventually the tractor starts and runs well. Looking for other ideas.
 
We have a cub that was acting the same way. We swapped the mag for a distributor and it fired up immediately. Spark plugs appeared to have good hot spark with the mag, but apparently not. Luckily we have 9 cubs and tons of parts so the swap was easy. I've been told that the mag can have weak magnets, causing weak spark.
 
I had thought about selling my Cub at one time as I have other small tractors and find it hard sometimes to find jobs for all them but when I read about your adventures with Cubs it has made me want to stay in the club so mine stays. Mine has a 1-pt hitch and I have a woods mower for it so I play with that once in a while. I don't have any other implements for now.
 
With a 12v driving the starter, it can spin fast enough to just prevent the impulse from actually working and slow enough to not make good spark. Car sized battery cables can reduce the spin to allow good impulse. 4 gauge wire. An experiment might be to disconnect a battery cable, and use a cheap booster cable to connect that bat post to the terminal. (leave the black cable unused) If that works, the cheap cables might just fix it. Jim
 
Along the line of what JAN suggested, try just pulling the starter rod until the engine starts to spin, then release it. As it starts to slow, the impulse will do a solid latch-in a couple times. It may be enough to make it start.
 
Had cub engines on Baler and combine , with mags ,left them outside in all seasons .To start. Made a one ,rotation with crank with choke closed , opened choke valve and they started.
Never did anything to those engines .
Best engines one could ever want , quiet smooth, that my opinion.
 

We sell tractor parts! We have the parts you need to repair your tractor - the right parts. Our low prices and years of research make us your best choice when you need parts. Shop Online Today.

Back
Top