Are you using Champion W20 spark plugs?

BButturff

BButturff

Senior Member
There has been plenty of discussion on this forum and others about spark plugs, heat ranges, higher compression heads, hotter ignitions, what plug to use and what not to use.


I would like to hear from people who have a stock Model A head, stock Model A ignition and otherwise stock Model A engine that are using, or have used Champion W20 spark plugs.


I have gradually been going up the heat range chart and am currently using Champion W18 spark plugs. My driving is about 85% small town streets that don't exceed 30 MPH. The W18s aren't super sooty but maybe W20s would be an improvement.
 
If you are checking for black carbon on the Porcelain part of the plug then it might be too cold or trips are too short and too much idling time.

If you are checking the steel part of plug then I would expect it to be black and Porcelain to be tan or brown.
 
I'd say that with your type of use the W20 will be fine. I don't believe you can have to hot a plug for that use ( light throttle and very low load).
 
If your plugs are fouling that easily, I would look for the root cause. Is it fuel or oil?

A buddy of mine had plugs sooting up quickly. After checking coil polarity (it was correct) he started looking at the carburetor. He swapped over the carb from his second Model A and that cured the problem with plugs sooting up.

So we opened up the suspect carb and studied all the jets, the ports, the GAV, etc. We found that his early-29 carb originally had a brass jet down at the bottom of the GAV driver hole, but someone had left it out in the past. So his GAV circuit was really dumping too much fuel in (no little hole for the GAV needle tip to seat into).

We added the missing jet and his plug fouling stopped.

A fairly simple solution, once the problem was found.

Bottom line, I don't recommend you go to the W20 plugs, but instead figure out why the other plugs are fouling and try to address that.
 
Benson said:
If you are checking for black carbon on the Porcelain part of the plug then it might be too cold or trips are too short and too much idling time.

If you are checking the steel part of plug then I would expect it to be black and Porcelain to be tan or brown.
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Yes, and that's my understanding as well. But it's very hard to get an accurate reading from Model A spark plugs when the car is driven as I mostly do. A long run of 20 minutes at 45 MPH with a quick shutdown and plug check is needed. In my mind, I could possibly use the W20 plugs for around town and the W18 plugs for "out in the country" club tours.
 
Jim/GA said:
If your plugs are fouling that easily, I would look for the root cause. Is it fuel or oil?

A buddy of mine had plugs sooting up quickly. After checking coil polarity (it was correct) he started looking at the carburetor. He swapped over the carb from his second Model A and that cured the problem with plugs sooting up.

So we opened up the suspect carb and studied all the jets, the ports, the GAV, etc. We found that his early-29 carb originally had a brass jet down at the bottom of the GAV driver hole, but someone had left it out in the past. So his GAV circuit was really dumping too much fuel in (no little hole for the GAV needle tip to seat into).

We added the missing jet and his plug fouling stopped.

A fairly simple solution, once the problem was found.

Bottom line, I don't recommend you go to the W20 plugs, but instead figure out why the other plugs are fouling and try to address that.
Click to expand...


Thanks Jim. My engine is very well sorted out and is timed properly, starts easily, idles well, has no vacuum leaks, excellent compression due to a recent rebuild and a Zenith completely rebuilt by an expert (he's no Paul Shinn but is a very close second). On those rare occasions when I do take my A "out to the country" the W18 plugs do clean right up. But I do so much slow driving that I'm wondering about using W20s in town and switching back to W18s for something like a club tour.
 
nkaminar said:
Do you run a thermostat? That may help keeping the plugs from sooting up.
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Hi Neil, yes I have a 160 at the bottom of the upper hose just above the water outlet. It warms up quickly and runs about 170 on a 90 degree day. If I block the radiator with cardboard it goes to 180 idling. Thanks.
 
I will gladly walk through some basic diagnostics over the phone, live while the engine is running. PM me a phone number and we can set a day/time. I suspect your carb is running rich. Easy to see in about 5 minutes.
 
I've run W20's since I've had A's, 40+ years. Never had a problem. From worn out stock engines to my current engine of counter weighted crank, stipe 330 cam and snyder 5.5 head.
 
I'd try shutting the GAV completely shut once it's warmed up and see if that alone will fix your problem. the A engine was designed to run a touch on the lean side and the GAV was intended to give a dose of extra fuel for low altitude and cold running. i start mine on 1/4 turn and completely shut it off once it hits 140F. do the aforementioned and once it's completely warmed up while idling adjust the idle air mixture screw in until it starts stumbling and note the position, then start counting the revolutions counter clockwise until it stumbles again, note position, then go half way in in between and go just a touch counter clock wise. also set the idle down when fully warmed up to allow the transmission to engage first with no grind after depressing the clutch on a 1-2-3-4 count. then drive the daylights out of it.
 
Check your head spark plug thread depths, should be close to 3/4" for std compression head. 520 (formerly W20) plug reach is 20.6 mm (13/16), 518 plug is 19mm (3/4") ; so electrode doesn't protrude too far in to the combustion chamber. 518 threads are / or may be too deep for h.c. heads. This is with supplied gaskets.
The gap may change also.
 
Let's talk sooting problem.

My car has twin Marvels and had a terrible sooting problem that I could not figure out, no matter what I tried.

After talking with Dave Renner he suggested that the issue could be the GAV's. The reason is when the marvell threads on the GAVs were tightened down tight, you think the GAVs are 100% shut off. But they are not, and therefore do not seal at the bottom and leak. Kind of like leaving the GAV's at 1 turn, but the GAV is closed tight.

Dave makes his own GAV's, better than the original. This immediately solved my sooting problem.
 
I have a 5.5 head and was using W16-way to cold as I was sooting up like nobody's business. Changed to W18 which I think are the equivalents to original Champions, the sooting went away. The porcelain went from sooted and black to clean and white. I am running a Marvel Carb which I may have to open just a crack to get the tan porcelain.

Mike
 
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