Spark Plugs on a B

Hey guys,

Been having a problem with the 51 B running rough lately. I figured points needed replacing. Sure enough, burnt pretty good so I replaced them and gapped to .20 (delco distributor). Put new AC C87 plugs in at the same time. Fast forward about a month. Been using it lightly, hauling produce out of the garden and pulling the sprayer. Not hard work at all. Starts running rough again. Check points and they're pretty black. Plugs fouled out with dry black soot. So, I'm thinking I'll replace the points and plugs again, but I'm going to put some new wires and a new cap on also. My question is, what would cause this? I haven't ever been into the carb on this tractor so that could be causing some of the problem, but still don't explain the points burning so fast. The coil is one that requires a resistor. Resistor is good, by the way. Could the coil be going bad? Could the condenser be going bad and causing too much voltage to hit the points? I'm kinda at a loss as to what to do here. I would appreciate any advice anyone has.

Mac

Black dry soot on the plugs sounds like it is running too rich. Adjust the carb. leaner and run hotter spark plugs. I run autolite 388. Are you running 12 volts or 6 volts ?

If you are using a coil with a resistor, then you must have converted your B to 12 Volts. For best results the coil and the resistor need to be matched. If you go to NAPA you will find that a coil for a mid sixties Chevrolet requires a 1.8 Ohm resistor. A coil for a Chrysler product with point ignition requires a .5 Ohm resistor, and a coil for a 12 Volt Ford requires a 1.35 Ohm resistor. Mismatching these coils and resistors can cause problems. For example using a .5 Ohm Chrysler resistor with a Chevrolet coil would cause too much current flow and burned points. The opposite situation occurs if you use a 1.8 Ohm Chevy resistor on a Chrysler coil you get too little current flow and weak spark. Another option is a full 12 volt coil that does not need a resistor. What is your charging system voltage? If too high you could burn points. Does the tractor have a lot of blowby? Oily vapor inside the distributor is another possibility

Sorry guys, should've said: it's a 12v conversion. I did NOT do the conversion. Had I been the one doing it I would've never put the resistor type coil in it. I may wind up replacing it if someone thinks that could be a problem. There is no oil present on the points, and tractor has very little blow by. I have tried leaning the carb idle out, but if you lean it out anymore than it does it "hunts" at an idle, like it's starving for fuel. Maybe I should have the carb done?

Thanks, Mac

Mac, so often if the plugs come out flat black sooty (that's excess unburned fuel) and fouled here are some things that work for me.

1) Run the carb as lean as possible. Also insure the FLOAT LEVEL is set correct and the carb bowls vent is open !!!!!
2) Insure the choke butterfly plate is opening full and staying open
3) Insure theres no restrictions in the air inlet piping and air cleaner
4) Use shutters or other radiator air restrictors TO GET AND KEEP THE TEMP UP TO 180 OR HOTTER
5) Try a hotter plug. The Autolite 388 is a tad hotter then the 386 while the 3116 is NON RESISTOR PLUG
6) Use wire core plug wires NOT carbon core or suppressor wires

Since its 12 volt you can use EITHER a full 12 volt rated coil orrrrrrrrr a 6 volt coil plus an external series voltage dropping (12 down to 6) ballast resistor. NOTE the resistor is sized "approximately" the same ohms as the coils LV Primary winding resistance so it serves as a 50 50 voltage divider dropping around 6 volts across the resistor leaving 6 across a 6 volt rated coil. A typical 6 volt coils is around 1.2 to 2+ ohms (maybe 1.5 average) and a typical old tractor ballast resistor I have seen is in the 1.2 to 1.8 ohms range.

NOTE if the points are switching too much over 4 amps cuz either the ballast or coil is sized improper, they will burn prematurely. IE for a 12 volt system and 3 ohms total (coil and any ballast) primary resistance, that's I = 12/3 = 4 amps. For a 6 volt coil on a 12 volt system its again coil (say around 1.5 ohms) + ballast (say around 1.5 ohms) = 3 ohms so again 12/3 = 4 amps. If the points are switching a lot more then 4 amps they will burn premature. CHECK COIL AND ANY BALLAST IF IT HAS ONE

NOTE if the condenser is bad or open or weak or not sized proper that also can cause premature points burning

If ignition is good and you run at 170 to 200 degrees and the choke is open and air inlets and cleaner is all good YOU MAY HAVE A CARB PROBLEM

Hope this helps

John T Retired Electrical Engineer

Thanks John. A lot of information to take in there! Ill look at all those things tomorrow. I'm thinking since this is a recent problem I might check into the condenser, as it could be the culprit. The carb doesn't seem to be the problem, other than I probably have it too rich. Ill let you guys know something tomorrow, I've been to the sale barn all afternoon and only just got home. And boy was it hot!

Thanks again, Mac

I like running the float to the 1/2" height like the older models rather than the 3/8" height called for. When set at 3/8" when on rough ground or bumps seems like you can get puffs of black smoke easier from extra fuel splashing around.

Youre most welcome. I have seen brand new condensors be bad right out of the box. Trouble is you cant tell by looking how bad if any at all they actually are, that takes a full blown capacitior tester. For light duty use its hard sometimes to get and keep the operating temp up above 170 or so, that's where shutters or radiator air flow restriction can help. Hot plugs, good hot spark, lean carb, free inlet air flow, temp over 170 or 180 or more was my goal. Back in the day when those tractors were ran long n hot n hard hours on end you didn't have the flat black sooty fouled plug problem so much.

John T

Mac, all these are very helpful...BUT, due to the design of the earlier JD 2-cylinder engines, when they Idle a lot, the will foul one plug

sooner or later..!

I suggest that you always carry a spare set with you ( Autolite #3116 I prefer)..nothing like having to run it on ONE cylinder..!

Well guys, I think I got er fixed. Seems like it was a combination of a couple things. I replaced the condensor with a know good one, and cleaned the plug wire ends along with the cap nipples. Some new ac87 plugs and we were off to the races. I went and plowed a while, and got her good and warm and after a couple small carb adjustments she purrs like a kitten. Well, as well as a 2 cylinder can purr. Special thanks to John T for all the ideas to try, you were spot on with everything, and it made me really go over the electric system with a fine tooth comb.

Thanks again everyone, Mac

THANKS for the feedback, good news

John T