The right spark plug?
 

Last summer, I decided to try the Champion RJ12YC plugs that burn hotter and penetrate deeper into the head. The hope was that these plugs would burn more efficiently with less fouling in a cool running A-4. However, there was actually a lose of power. When I pulled off one wire at a time while the engine was operating it became apparent that #3 was not firing accept intermittently. I then swapped wires but no change. I placed the plug in other cylinders and it was clear that the problem was that plug. Then, just as I was placing the wire on the top of the plug and causing it to arc, the plug would work and the cylinder would fire happily as long as I held the wire just off the top of the plug. When the wire was properly in place - no firing. When that RJ12YC was replaced with an RJ8C the engine ran great with lots of power. So, I got another RJ12YC plug to replace the one that was apparently bad. When installed, it fired normally in #3 but the plug in #1 would fire only intermittently. I came to the conclusion that with four RJ12YC's installed there was an incompatibility with my coil, or condenser, or something. I put the set of RJ8C's back in the engine and enjoyed great power with no more problems.

I would appreciate any comments as to what was going on. And I want to alert others who may be tempted to experiment with the RJ12YC's.

We finally got through to Champion Technical Service for an explanation of this problem and more or less drew a blank. They could only speculate that the plug probably had a hairline crack or other defect in the internal porcelain insulating material. Whatever the exact nature of the defect, the insulation quality of the porcelain could apparently control the secondary discharge with the increased resistance imposed when the lead was held away from the plug, but would break down and follow some other path to ground when the lead was connected to deliver the entire secondary discharge.

Don

plugs
 

I had similar experiences with the plug and wires that you did and found the same results. The J8C's ran fine and the RJ12Cs (and the NGK brand plugs) ran poor, and I had new wires. Mine was on the number one cyclinder with bad fouling. I recently took off the side access plate and found a bunch of crud had blocked the cooling passage around half of my #1 cyclinder. I cleaned it out by poking through the drain hole underneath the access plate, then put in the RJ12Cs and now its running fine with no plug fouling (yet at least) and smooth as with the J8C's. I may be way off base, but I hypothesize that without the cooling water flowing all the way around, my #1 cylinder was running hot and then I added a hotter spark plug and it wouldn't run well. Going back to the cooler J8C plug appeared to allow it to operate again. I put this up in the cooling forum too, and am interested as you are to hear some feedback. However, there is more room around the middle cylinders so it would be harder for them to get silted up like my #1 was. I think #4 would be likely to silt up as well with the tilt of the engine allowing fine particles to settle and solidify there.

I see you switched plugs into other cylinders and were able to reproduce the effect on the other cylinders, so your problem is likely in the plugs, but I think its interesting that our symptoms were the same. I'm trying to become more scientific in my troubleshooting and I wish I had played around with it more when it first happened.

I had problems aith Champion plugs and switched to Autolight 437's .... much better plug and no problems...they burn cleaner and last longer.

David

On the 437's, whats the gap?

Yo can gap the 437's just like the Champions .025.... the old hot rodders used to open up the gap and get a hotter spark.... this is just an A 4 .. the .. .025 will work fine.

David

I have the Autolite 437s also, but I gapped them at .035 as specified in all of the A4 literature. Should I have gapped them at .025? If so, why?

Thanks,
Charles

I think that you will find that .035 may be okay for the 437's... I am trying to think back... I may have gapped mine to .030....

Generally speaking , the A4 runs cool... the plug is just a little bit hotter than the Champion 12... somewhere, they are listed as being in the same heat range... I can tell you from experience that they perform very well and last. Once you get the engine hot and have run it under load, pull the plugs and look at them... If you system is fine from the electronic stand point, you will find th eplugs lookng almost like new. I hav enever had a foul 437

David

Where did you find out that you could use RJ8s? I am having a terrible time finding four RJ12s at the same time. Buying plugs usually requires three stops.