Fuel Grade?

[WKPoor]

I've posted this topic on the Farmall Cub forum because I've had this trouble with both my Cub and H model tractors. The spark plugs in the pic are out of the H but my Cub plugs look identical to the fouled one. Both plugs pictured were run in the same engine. Both plugs were installed new from the box. Both plugs have the same gap.I have tried all types of plugs (5 or 6 different mfg and heat range). No adjustments were made to carb or ignition. The fouled plug is what has plaqued me for months running on pump gas. That plug was pulled out after only about 5min run time and the engine was missing so bad it quit on its own. All of the plugs I tried fouled the same.Soot gets all over the tractor and makes a mess. Both carb and mag have been thoughly checked and fuel adjustments were as lean as possible. This problem got worse as the outside air temp. went down. The clean plug is after several hours run time on 100LL Aviation fuel in very cold temps outside. There is more I know about this but I'll stop here and let you guys digest this much before I say more. I figure I'm not the only one having or had this problem.

[John *.?-!.* cub owner]

Since I usually get 2 or 3 years to a set of plugs, I don't have an opinion, but I do see you support one of the largerl businesses in my area

[Eugene]

Just throwing out ideas.

(1) Check the carburator float level - sticking needle valve - chock not opening fully. Someone will jump in with the correct web site address for setting the carburator float. From the looks of the plug it's a fuel problem.

(2) Plugged air cleaner?

(3) Weak spark? Ignition timing off?

(4) Probably not - Really old bad gas. Intake manifold not heating up.

I haven't had a problem running my tractors on regular, pump grade fuel.

Interested to find out what the solution to the problems was.

[Larry in CO]

Last week, Chubbie Cubbie - named by the 3 year old grandson - wouldn't start. I changed the plugs and they looked just like the one on the right above. I checked the heat range on them and someone before me had put Champion D-16 range in. I replaced them with Champion D-21 range and that seemed to solve my problem. Chubbie doesn't get much work, just running around the neighborhood, so the hotter range seemed to help quite a bit. I don't know what heat range you're using, but you might want to check this out. Larry

[Larry in CO]

Woops, missed the comment about you trying different heat ranges. Sorry. Larry

[mike mix]

The first item to check is the health of the engine. Whats the compression of each cyl. As posted above make sure you have the correct heat range of spark plug, timing correct, carb float level correct.
The biggest item is old fuel. In the northern parts of the country we have summer blend & winter blend fuel. Summer blend does not vaporize well in the winter and you end up with hard starting and deposits on the plugs. Winter fuel vaporizes easy and in the summer you will end up with gas vapors in your engine oil, making the oil thinner.
These old tractor engines have low compression engines and are meant to run on regular grade of fuel. Any High test or premium grade of fuel will cause problems and deposits in the engine.
Mike

[RedNed]

WKpoor,Nothin like Avgas!, Sunoco 260, Cam 2 racing fuel.Alot of moisture in the mixture?Saturation?100 percent. Hey I am about 1/4 mile from the Long Island Sound.Talk about water.............salt .Advection fog.

[WKPoor]

Someone mentioned carb float level. That was the first thing I checked. Carb is per the book. The pump gas was fresh. Someone else mentioned engine health. the H has a fresh rebuild-Super H bored out to 169cid high top pistons and milled head resulting in over 170lbs. cranking pressure. Also carb is super H size. Aircleaner was completely taken apart blasted, painted and reassembled with fresh oil. Had 3 different rebuilt mags on it-all prooved to have adequate spark potential. I am going to try a battery ignition at some point so I'll have timing options that don't exsist with the mag. Now that I've found a fuel that I can run the power is to say the least, monsterous. I must sat again this same problem plaques the Cub. Has since I got it over 8yrs ago. So its not unique to the H. I'm curious why my cars aren't doing it. Same gas was used in both.Maybe it's the science in combustion chamber design. I don't think there is any alcohol in AvGas and I'm sure there is in the pump gas.

[rick 48 cub]

Hi WKpoor,

I have the same problem - good compression, lean fuel, hot plug, fouled plug in just a few minutes of running.

My spark was a little weak so I am having the Magneto rebuilt and remagnitized right now. Hopefully this will solve the problem - but I have a feeling I am not going to be that lucky.

I will keep checking this posting for some practical ideas.

Rick

[WKPoor]

Hi WKpoor,

I have the same problem - good compression, lean fuel, hot plug, fouled plug in just a few minutes of running.

Rick, Good to hear from you, sorry your having my same prob. but I haven't read much on this topic on the forum. It just seemed to me I can't be the only one. I too thought it must be a weak spark but I found that it wasn't really the case. However I see you also are running a mag. If your mag can jump a 3/8" gap to the plug when its running I'd say you got more than enough spark. The only major dif between the mag and batt ignition is the timng issue. However according to book high idle advance is about the same. I'm just wonding if the timing needs to be adjusted differently to optimize fuel burn for current pump fuel. By upping the octane I've compensated for the timing issue. The higher the octane the faster the fuel will burn thus timing can be retarded. The pump gas may need more advance to fully burn it and result in higher combustion temps. Plug temps needs to be 450c-850c to keep deposits from forming.

[Eugene]

Plug wires - are they metal stranded vs. the carbon thread style? Magneto ignition systems do not function well with the carbon thread style plug wires.

Fresh out of ideas. But if the problem is common to both the H and the Cub there is probably has a common answer.

[WKPoor]

Plug wires - are they metal stranded vs. the carbon thread style? Magneto ignition systems do not function well with the carbon thread style plug wires.

Eugene, Yep I tested this issue also. I'm now using 8mm copper core wires. I tried carbon and believe it or not they change the impeedance enough that the engine sounded totally different and of course the plugs still fouled. I went back to copper wires brandy new.

[George Willer]

The higher the octane the faster the fuel will burn thus timing can be retarded.

Bill,

I'm sure you didn't mean to say it that way... it comes out completely backward on both counts As I'm sure you know, higher octane gas actually burns slower. Retarding the spark is the cure for too low octane which can cause knocking. Higher octane makes it possible to advance the spark some without causing detonation.

In any event, normal lowest grade pump gas is higher octane than the Cub was designed for. There is no advantage at all for going to higher grades in a properly tuned engine.

[cjpenny89]

I have similar problems first I thought it was the D-16 plugs I was using but I put in D-21 it helped delay the foul problem but didn't fix it.
Then I did the usual wires cap rotor points changed the coil didn't help.
Then it hit me I played with the timing and it was off that really helped but did not do it completly. Next I rebuilt the carb to factory specs and it ran better again but not great. So I did the test to actualy see if the float level was right. Well guess what when I hook the clear house up and tested it that way I had 3/8 to 7/16 to much fuel in the float bowl.
So I tore the carb off readjusted the float put it back together and
re-tested the fuel level. This time it was right on and I have not had a problem since. So even though you set the float to factory specs doesn't mean that it is giving you the correct fuel level in the carb. I was getting way to much fuel even after I leaned it out all the way.
Go to Lurker Carls website he has a great write up on this even though it is a cub carb and not for the H.
copy and paste this in your webv browser and it will show you how to check your fuel level in the carb and let us know if that was it.
Chad
http://www.cleancomputes.com/Cub/Mainte ... index.html

[moe1942]

The two most common causes for fouled plugs seems to be improper fuel/air mixture and/or timing. The "H" with 170PSI comression should love the 100 octane fuel but the Cub should run great on quarter master, 80 octane, gas. Since that isn't available 87 octane is great.

Some questions I would ask myself:

1. When did they run OK without fouling plugs?
2. What took place just prior to plugs fouling?
3. Are the tanks free of water?
4.Are the ign systems producing a good hot spark?
5. Should I switch to a different brand of plug. (Champions aren't the same quality IMHO) Quit using them in my Harley...
6. Am I sure the choke plates are fully open? (Don't ask )

Since they are both fouling plugs there is a common denominator between the two... like fuel...

Hope this helps some. You might even have to resort to indexing the plugs to over come a gremlin.

I think if none of the above apply I would play with timing, especially on the H. I use a vacuum gauge to time mine.

Good luck and please tell us what solves the problem..