I searched MTFCA for T plug gap, and it appears 1/32 is correct. The manual on our Model K says 1/32 to 1/64. I'm having trouble with low end power (lugging when shifting from low to high) and have been trying to "adjust" away the problem with the carburetor. However, could the problem be plug gap?
For more low end torque (when shifting to high at low speed) should I have wider or narrower plug gap? The car misses and sputters, until gaining a little speed. At idle and speed it runs great.
Ideas, more plug gap, less plug gap?
The instructions included with every Champion X plug state they need to be set at .025" for best results. I can confirm the manufacturer's recommendation.
I'd try less gap on the buzz coil fed plugs.
Are you sure there's no vacuum leak? I squirt water around the intakes at idle and look for sputtering.
Timing? Carburetion? Doesn't sound like plug gap to me. I really don't think plug gap is really fussy, I always set mine by eye.
I can confirm that my T will not run properly gapped at .025" I've done it with three sets of original X's and two sets of repro X's and an original set of Wards. Mine runs best at 1/32 of an inch.
"I'd try less gap on the buzz coil fed plugs."
I take that back. The HT magneto output is more affected by RPM than a battery, huh? Try closing those gaps.
If you have a vacuum leak, you adjust the idle with a richer than correct mixture. Then, demanding power at low rpm by open throttle decreases the effect of the leak, and the engine floods. I would mount a video camera to view the exhaust, and see if black smoke comes out when shifting to high.
I'm with William. I know some Champion info says 25, but I always go 30 because no matter which car, which carburetor, which carb setting, 25 runs like crap at low end for me! 30 just always seems to work as a slam dunk no questions asked.
I don't know about a 'K', but you have nothing to lose just trying a wider gap...it will either run better, or no change, or it will run worse, or not run at all If worse, then you know to look elsewhere....BTW how clean is clean when you pull them? That might yield more clue.....
I'll pull and check them. Just remember, I have three times as many to check (6 on mag, 6 on coil, dual independent ignition).
The greater the gap, the greater the voltage required to make the jump. Also as compression increases, the greater the voltage required to make the jump. Demanding power at low RPM will require a higher voltage to get good spark than at higher RPM less load condition. So the solutions are less gap, or higher voltage.
"I can confirm that my T will not run properly gapped at .025" Mine runs best at 1/32 of an inch."
John is in fact totally correct in the gap v. high tension voltage physics.
However, as pointed out on T's, and adding that for years I was the odds on favorite as the local regional track quarter-mile top eliminator with super stock as my basic class with another brand machine. I found the same thing there, pulling a gap in gives you best shot at a good hot spark, (even indexing plugs to the head I can agree with as it just eliminates a minor possibility that may not matter at all) but in my own experience there seems to come a point where too close is too close and it still is an actual gap, and things want to bog on a power call. As Ted also points out the opposite does not hold true. At the other extreme once you have the Swiss watch behaving 'Swiss' the upper end gap is not all that fussy (within reason).
I don't know why this too close phenom exists, but my seat of the pants guess is that based on all the other variables involved, the plug does fire, there just isn't enough vapor in the gap to get a 'timed' spark. Sounds a bit ridiculous, but thats the only conclusion that makes sense to me.
As several point out already, on a T set to that recommeded 0.025" more than a few will chime in saying they believe that carburation is correct, believe they are tight, and yet it gives them groans starting or wants to idle rough and spit at gear change. Opening the needle valve isn't helping. First answer by others on the forum is open the plug gap to 0.030" and the reply more often than not is 'thanks, that did it'
I have not a clue how a 'K' works or what its compression even is...but I do think that Rob's answer is in a Goldilocks solution. Try a little wider...see what it does...or...try a little closer and see what it does...it's like going and getting your eyes checked.
You have the answer there, George, but must not realize it. There is no current in a coil's secondary until the spark. A coil builds up to high voltage like a ramp. The narrower the gap, the sooner the spark occurs, lowering the voltage at time of spark.
Gap plus air density (compression) equals resistance, which is the voltage needed for arc-over, spark. Likewise a lean mixture has more resistance than a rich mixture.
Once you have arc-over, the air in the gap is ionized and its resistance drops drastically to relatively near zero.
E/R = I
Voltage divided by resistance equals current. Resistance (gap plus compression plus mixture) is fixed until you change it. That determines the voltage required for arc-over. Small gap (low resistance) takes less voltage, of course. Low voltage after spark and ionization means less current draw, and less power in the spark to ignite the fuel.
Opening the gap requires the coil to ramp up to higher voltage before arc-over and ionization. The higher voltage and low resistance of ionized gap causes the current draw to be higher.
Power equals voltage times current.
Too much gap, and you draw too much current and can overheat the coil, as I paid a lot to learn after cooking two very expensive coils in the Bendix magnetos in my Franklin powered Bellanca. Too much gap can also cause coils to arc over internally.
Even back in the era they knew to place the sparkplug near the intake valve and fresh mixture to assure ignition. That's why I knew the Lizard head would be a loser as soon as I saw the sparkplug above the piston.
You couldn't find a spark plug further away from the inlet valve and over the piston, than the 4 valve Rajo head, works fine.
Ah, silly me, after checking on that, the inlet valve is over the piston, as is the plug too.
Neither the coupe or the fordor like .025 gap. I opened them both up to .028 and they run much better.
Thanks guys. I was working with the K again this afternoon. I'm trying to get it to "lug" to where I can put it in high gear at 4-6 mph (and I know it can be done because a friends K does it) as the owners manual says.
I'm at the point where it will pull up to spread, so the carb is doing pretty good. I'm going to check the plug gaps tomorrow or the next day and see if they are gapped a bit wide. If so, maybe a little less gap will help (or not).
If the plugs are not fouling I doubt anything plug related will affect the performance at all. Maybe try shifting at a higher RPM?
Or it could be you need to use less spark advance in low gear and for the first few seconds while accelerating in high. After the car is up around 30 MPH advance the rest of the way.
I've always used spark when pulling a hill or after shifting to high at a low ground speed. One thing I've noticed is when the magneto is on, the spark doesn't make much difference (unless it's much too advanced).
This is not the "correct" carburetor, so I really don't know if it is matching up well, especially at the point where I'm asking a lot of the ignition and mixture, pulling a six cylinder 2600 lbs car from 5 mph to 40 plus mph in high (direct) gear.
Maybe your carb is too large for the low rpm, low vacuum and not drawing good. What size is it? I bet somebody would have a size smaller you could try.
How is the carb attached to the manifold?