Fouled Plugs

[Bob Grieb]

I'm listening - It was Donny who recommended the AB 6 to me whe nI first put the Cub back together. At the time I had Autolite 386's.

[Don McCombs]

Mike,

That chart doesn't show a Champion cross for the AB-6.

[Hengy]

I'm listening - It was Donny who recommended the AB 6 to me whe nI first put the Cub back together. At the time I had Autolite 386's.

I had someone else relay to me that Rudi recommended the AB-6 as well... Wonder if the AB-2 is a hotter or cooler plug? Wish I had Excel on this machine so I could read the spreadsheet myself!

Mike in La Crosse, WI

[Don McCombs]

Mike,

Here's a non-Excel version of the same chart.

http://www.angelfire.com/extreme4/skidoolympique/SPARK_PLUG_CROSS_REFERENCE.htm

[PAUL K. in N.H.]

I just did the cross on that last chart and it looks like AB2 for both the D16 and the D21's.

Paul K. in NH

[Hengy]

Well that is contradictory, isn't it. The angelfire chart recomends A6 (NOT AB-6) as a cross for D16's, but doesn't reference D-21 anywhere on the chart... Though I can say, that it got difficult to scan through looking for it... there is no "search" function that I was able to find to look for D-21...

However, this website seems to contradict the spreadsheet...

All I know is that my AB-6's worked great until such time as I had to take the head off of my tractor to replace the cracked one... Is the AB-2 hotter or colder than the AB-6?

Mike in La Crosse, WI

[WKPoor]

This is one of those topics that pops up from time to time and I'll bet will continue. Cubs seems somewhat sensitive to plugs fouling and most people have experienced it at one time or another on Cubs. My first Cub was terrible about it and it was blamed on the Zenith carb. That same carb is now on a different Cub that has never fouled yet due to fuel but plugs get a little wet from oil but that doesn't cause it to miss. In my past experience dry carbon fouling will kill one quick.

[Bob Grieb]

Your description "dry carbon fouling" closely describes the condition I noted on the plugs I removed. They were easy to clean with a wire brush and functioned well when I reinstalled them.

Thanks

Bob

[WKPoor]

Hey Bob, I just had a thought on this subject. There has to be a common denominator on this fouling issue. It partly is overfueling as many Cubs have too large a main jet. And a weak spark could add to it. One thing I have noticed on a few Cubs and other old Farmalls as well is carbon build up on the exhaust ports of the block. My first Cub is out of service right now and when I took off the manifold the exhaust holes were seriously carboned up. I wonder if this is a cause or effect relationship to the plug fouling issue. When these carbon up air flow can't be as good as it should be.

[Bob Grieb]

It's an interesting thought but my manifold has not been on the engine long as I rebuilt the engine two years ago and have very few hours on it. I would not think it could build up that fast.

I am not sure if I told you but I had an .034 jet in the IH carb. I just ordered a .032.

Does that make any sense??

Bob

[WKPoor]

I can't remember for sure but I think optimal jet size is about the .032 size or close there of. How is the compression? Maybe low could make it run cooler and that might aggravate the problem. I believe ultimately plugs running the correct temp should stay clean. Its a matter of getting the plug electrode temp high enough to keep deposits at bay but not to hot so as to promote good plug life. Were they all fouled about the same? And does your choke open fully? Dry fouled plugs is most likely a tuning issue which narrows it to fuel delivery or spark. Is it mag or batt ign?

[Bob Grieb]

I have not checked the compression as I just installed new rings two years ago and all plugs were coated alike. It is a mag system and spark "appears" to be good. When the plugs are cleaned the engine fires immediately. I am not certain but I believe the choke is fully open. I will recheck that in the morning.

Thanks for your interest

Bob

[WKPoor]

I have installed new coils on 2 mags and I think the news ones are stronger than the originals. My current mag starts my Cub so easy I don't see the need for a starter and that motor is completely wore out but doesn't foul plugs. They do get a little wet from oil though.

[Bob Grieb]

The compression is good and even. I think I will wait until after I install the new jet (on order) and if the problem continues I will look into the mag issue.

Thanks

Bob

[Donny M]

According to the NGK cross-reference chart, the D21 crosses to an AB2.

http://home.att.net/~ngkaz/wsb/html/view.cgi-home.html-.html

I've been using NGK AB-6 plugs for several years without a problem. I got the cross number from NAPA. I also believe that Bud crossed the D-21's to AB-6 also.

Don, is the AB-2 hotter or colder than the AB-6 and how many steps in between