Warm Starting Difficulty--Weak Spark Plugs

Mon Apr 29, 2013 8:34 am

My 1958 Farmall Cub would not re-start well when warm. I bought the unit about two years ago and had finished a whole tractor restoration this past winter. The Cub would fire-up fine when cold but progressively got harder to re-start when warm. My restoration had included just about every system and component...except the spark plugs.

The Autolite 3116's that came with the tractor looked okay. I cleaned and re-gapped them and they performed when the tractor arrived. Only after checking and re-checking the fuel system, carburetor, governor, distributor, timing, compression and valves (tappet gap) did I give the spark plugs some thought. I replaced the original plugs with Champion D21's which are understood to be "hotter" spark plugs. The hot start problem was found and eliminated!

So, to help others who may have tractors with the same symptoms, I offer this post. I have used Autolite 368's with no issues and have years of trouble-free service from Autolite 3116's. Right now, both of my tractors have Champion D21's and the performance is great.

Re: Warm Starting Difficulty--Weak Spark Plugs

Mon Apr 29, 2013 9:45 pm

I have run into a similar problem, and changed plugs a couple times till they failed to solve the problem. I finally figured out it was a coil going bad and the spark was getting weaker all the time.

Re: Warm Starting Difficulty--Weak Spark Plugs

Tue Apr 30, 2013 5:06 am

I also suspect you are seeing the start of a coil problem. Keep an eye on it, and replace the coil before you go through too many sets of plugs.