F-20 Spark Plug Issue - long post

I have 2 running F-20's. I've had Autolite 3077 plugs (the really hot ones) in them for some time. They both run great, with almost no misfires. Recently the 39 (hand-crank) has been really hard to start. Once started, it runs great. I've changed the carb and mag with no noticeable difference in performance. The other day I was using the 34 (electric start and loader) on a large mulch pile. I managed to kill it and it would not restart. I let it cool awhile and with much persuasion, it finally started hitting on one, then the rest of the cylinders kicked in and it was running fine. I shut it off when I was about finished to clean up some rubbish and it would not restart. I had to pull it to finally get it started. The next day, it would not start. I took out the plugs and they looked good. I changed the mag. Still nothing. I finally put in some 3076 plugs and it fired right up, but ran rough as usual with those plugs. Just for test purposes, I put some old 3076's in the 39 and it started on the first pull after choking. I put a new set of 3077's in the 34 and it started right up. I was using it today to move some dirt and when I shut it off, it would not restart. I put in the 2 easiest to install 3076's and it started right up on two then the other two kicked in. What is going on here? I've never run into anything like this in all my years of working on engines. Also, what make and model plugs are you guys using? Sorry for the length of the post.

My guess is you have two mags that need a tune up.

Make sure that both your magnetos are in good working condition and have a GOOD BLUE SPARK. If that is not the problem, it may be your plugs, try switching to Champion plugs, I've had much better luck with Champions than I do with Autolites. My Farmall H had new Autolites in it and 2 plugs went bad at the same time after very little use. I switched back to Champions and have not had any problems. We have Champions in all our tractors. Try them and see if it helps.

Good luck.

Andy.

While I dont have much older F Series Farmall experience I do have a lot of experience with mags in general and those plugs you mentioned. FOR SURE I have farrrrrrr less fouling problems using the deep reach hotter side wire electrode plugs like Autolite 3077 or AC W 18 (think thats the AC No.??), versus regular electrode cooler 3076 or the regular electrode Champion equivalents.

That being said and since magnetos arent very forgiving, Id look for a problem there versus any choice of plugs. Get the mags to throw a good visible blue versus any thin wimpy yellow spark and install a fresh set of Autolite 3077 n you should be off to the races..

John T

Simply this, you have to many F-20's....sell the "34" to me, problem solved!!

Andy,
What is the Champion number?
Thanks, Roland

I reckon I'd better keep it. Thanks

Mine too!

Champion W-20 should work fine.

Im kind of a newbie on here, but i collect nothing but Pre 39 IHC and have been through your dilemma before.

You have a couple of weak mags, plain and simple. they need to be gone trough and reconditioned. When all said and done, you should be able to bench test them with a big blue spark that you can actually hear 'crack' when the impulse snaps.

as far as the plugs your using, stick with the Autolite 3077's. CHAMPIONS ARE JUNK!!!!!!!!!! they were junk years ago and are worse now, trust me ive been down that road before too. Ive got over 20 Pre 39 classics here at home and every single one has AUTOLITES in them!! and amazingly enough, all mine run and run good :lol: