70D : Pony carbon fouling plugs

My pony has not been acting right lately, and I thought I might have a major problem. It was beginning to backfire, and not starting well, not running smooth at all. Well, I guess it's been a while since I really worked around a spark engine, so I finally pulled a plug and it was terribly carbon fouled. It has been had a ring job, and there is no oil involved.

I cleaned the plugs and it fired up and ran very well. That is for a maybe several minutes. Then it began to pop a bit, and began to lose speed, until it would die. I added a jumper to give 6 volts direct to the coil (just for a test !), and it picked up speed. Once it was back at top end, I could cut off the jumper and it would run on the reduced voltage.

I started the main engine and warmed everything up really well. Then I started at the timing, and it is right on. Points are new and set to .020". The plugs are clean and gapped at .025"

I shifted it to crank the diesel on full compression, and slowly turned in the load screw. The engine began to slow, so I began turning the load screw out. I had to come out a good 3/4-1 more turn to get it stay at speed at load. I think it likes to be 1 1/2-2 turns, which seems like a lot. I ran it for a while, and it ran out of fuel (from a full tank). I know they are not misers, but it really seemed to be using a lot of fuel for the task. Then I pulled out the first plug, and it is clearly carbonning up again, after just a few minutes run (see the picture). Air cleaner is clear, timing is right, ignition parts are new.

The last plugs I bought were NGK's, B6S. Guess I'll set out find the called for Champion J8C.

Questions are:

Would the next hotter plug be helpful ? My Champion chart shows the next hotter plug as J19LM, and then the hottest as J11C, or RJ12C in a resistor.

Anyone else have pony's that run this rich, or what might I do to solve this.

Looking for things to try. I don't want to put the hood back on until I have this figured out. BTW, any good way to change that plug the sits behind the lower left corner of the dash ?

Frank-in-Tallahassee
70D // 855

I used to use Autolite plugs on my '48 "A". They are manufactured at the plant in Fostoria, Ohio, where my wife is from. We lived there for 20+ years. My old "A" had a lot of Autolite engineering test plugs in her. Everytime I hear folks sing the praises of Autolites, I feel that ole' #595751 played a goodly part in the R&D. 25 years ago those plugs were so bad we used to call them "Ought to lite". They'd hardly fire in an old JD.

As of this morning it starts and runs fine. I am curious that I may be lossing voltage as the pony coils heat up. After a good warm up, you can hear it begin to stumble, and if I put 6 volts straight to it, it picks right back up. Maybe I have a high resistance connection, and as the pony runs, the current draw increases, and the wire resistor on the switch increases in resistance. I'll find it.

My multimeter must have too fast a sampling rate, because it can't seem to pick up a solid voltage reading. I going to have to borrow back my old Triplett analog.

Curious.

On the difficult plug, I use a box end wrench that has dog leg in it that allows it to get on the hex portion of the plug w/o the rest of the wrench hitting the cylinder head. I put "never-seize" on plug threads so once I break it loose I can turn it out by hand. Still not an easy job, but I know it can be done this way.

It'll be in Wednesday. I'll let you all know.

Now I'll go out and install my new J8C's.

F-I-T

I was leaning toward the "low voltage" premise myself. That would explain why the plugs foul more easily, and why the engine comes back up when I nudge the pedal enought to kick-in the by-pass line. I had taken that switch apart and cleaned it before, but maybe I'm in the market for a new one...I hope it's available. You know, for now, I could put a separate toggle switch on the side where to test it with. I have a spare resistor....H-m-m-m-m-m-m-m ?
As far as that plug goes, I can't even get my fingers on it. I thought I had done that before when the cowl was on, so I must be missing something.

Frank

Thanks for the recommendations. Some info:

- make sure the plug wires are fully inserted in the coils.

FWIW, when it quits, both coils quit. It's not like just like one pair of wires misfires.

- Try the J-8C, I've had real good luck with those copper plugs.

I'll head out for asome this afternoon. You don't think a hotter plug is worth a try ?

- Those little engines don't have real good oil control so don't use a synthetic oil as that can get into the combustion process & foul plugs easier.

I've been using 10w30. In fact the Rotella the main engine uses. The plugs don't look oil fouled, just dry carbon. She's running really rich.

- I have found that taking an old cheap pressed tube type plug socket & cutting it off at about the top of the hex will just slide over that L/R plug & allow a box end wrench to get a bite on that cut down socket & get that plug out quite easily.

Good idea !

- One last thought, you might want to reach in the #1 plug hole with a pencil & touch the piston, then rotate the pony flywheel to try & find actual TDC. Those pony ring gears will go on anywhere & unfortunately the timing mark is on the ring gear [your timing mark might be off]....

I'll check this out, but the distributor seems to be in what I would consider a "normal" position. Also, not sure, but I think I checked that timing mark position when I was re-assembling it...I usually do. Should a guy try a little more advanced to get it a bit hotter ?

I'll keep you posted after I install new plugs.

BTW, I think the charging is fine, but it really does need a new fan belt. I had a new one for it, and mislaid it while it was torn down, so I put the old one on it, and I think it is just too old, too stretched, and too slick. It full-fields fine !

Frank

First thing I checked was the resistance thru the OP switch. It's fine. The new J8C's made a MAJOR difference. Runs like new. It allowed me to really lean out the load quite a bit, and the idle a bit, too. It spins the diesel very well, and doesn't get that loading up it had before. Now that it's warmed up, I'm thinking I should let it scream for a while cranking the diesel to maybe blow some of that carbon out of there. That's what I'd with a large engine, put it on a load and let it go.

Bad idea ?

I don't know, I guess that those NGK's might have been the problem. I know folks swear about specific brands in specific applications.

Anyway, did you know that those J8C's are "small engine" plugs ? NAPA guy told me those were used in quite a few lawn mowers.

One more thing. A Tecumseh 6 hp tapered paper air filter will just slide into the pony inner air cleaner baffle just snug. I'm thinking of trying that for a while. I don't like the oil that can slop around and get all over the pony. I'd put piece of wire mesh in the outer baffle to keep any of the oil that the diesel might vent away from the paper element. I wouldn't think it would be much. Mostly fumes. The rate that I run it it should last for years if it doesn't get wet or oily. Then I could find another aircleaner pan, drill a hole in it and route a small line down and away if there was any drippage.

Bad idea ?

Frank

Wires are very good. I put in an entire "kit" from Magneeders when I first got it done here. I did replace the coils once, so I'll look inside of one and see if I have a different connection method, but I thought that it was that little double clip that clips onto the wire end almost like a spark plug boot and terminal.

I'll look at anything at this point. It had run so well, that now I am determined to track it down.

As far as that odd plug, I guess I'll just lift the steering support up and get it out.

Frank