Correct spark plug gap

D

denver9

Member
I am running a high compression head (Snyder's 6.5:1) on my 31 Model A coupe. I am also running it with a Weber 2BBL carburetor and electronic ignition. (First Street Ignition, Tulsa, OK).

Until recently it has purred like a kitten (Ran nice) with this set up,
Then I put the car in the shop for unrelated cosmetic upgrades. It ended up just sitting for almost a year. When I got it back it ran like a sick old cat.

At every stop light the engine would die. The only remedy was to set the idle to an unusually high RPM or pull the choke out a little (That seems odd and a bit contradictory for a rich running engine?).

Adjustments to the carburetor had little effect if any. I checked the compression and all 4 cylinders had excellent compression (100 +/-2 lbs). However, all 4 plugs were black and sooty looking, as though the engine was running extra rich. However pulling the choke out a little also seemed to help, which to me was rather odd, as I said.

After doing some investigative reading I find that it is recommended to have a fuel pressure regulator in the circuit set to no more than 2 PSI.
I have done that and I am about ready to install new spark plugs
(NGK BP R5 ES).

I am wondering if I need to regap the plugs or use them as they come out of the box? (.035 gap).

I would appreciate any comments (Constructive please) that any of you might care to share about this overall situation.
Thank you all,

Denver Howard, Hemet, CA.
 
Always check new plugs and re-gap if necessary. With a high compression head, I gap at .025. After driving a while recheck the color of your plugs.
 
I've seen lean running cars that actually DARKEN the plugs! I "feel" that the mixture is TOO WEAK to cause a good strong combustion & that gradually DARKENS/BLACKENS the plugs, because the fuel is HALF ASSED BURNED.
Bill W.
 
Agree with Tom. Unless the carb was drained, the gas may have gummed things up after sitting for a year. Sure you did not do anything else?
 
Tom hit the nail on the head. Carburetor jets tends to get deposits from dried gasoline and other additives put into the gasoline. Take the carburetor apart and clean-out all of the jets, and also clean the float valve.
 
Here is what I think happened:

The car was in the shop for a year.

During that time it might have been started any number of times for various reasons, like to move it outside to move another car to a different place in the shop, but never driven long enough to get the engine warm enough to clear the soot off the plugs which are now fouled.

I would replace the plugs and run the car.

Over 50 years I have used several types and makes of high compression heads (ranging from 5.2 to 8.25 compression ratios).

I found that they all idle and run better with plugs gaped at .035 ... I tried .035 ... .030 and .025 that experts suggested.

.035 always worked better overall.
 
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I agree with Benson. Also put fresh gas in the tank, old gas can be at least part of the problem. It should run better with .035" than with a narrow gap.
 
Plugs will foul also when repeated short trips are made to the Ice Cream Store with no time to get the engine hot.

My friend Rumble Seat used say that this only happens when going to the Ice Cream Store!

If you go to auto parts store (Or in Paul's case the Hamburger Stand, about 5 blocks from his house) the chances are much better that you will meet up with another "Gear Head" to race around with and engine will get nice and hot! :D :D

White Castle was another spot but it is 4 miles or so away by way of the highway ... gets nice and warm!
 
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"Fuel pressure regulator"

Pardon for the question, but does your car have a fuel pump?

+ 1 what Jim said ref the possibility of skunk fuel.
 
I put fresh fuel in, gapped the plugs at .035, and added a pressure regulator in the fuel line between the electric pump and the carb. It starts quick runs smooth but still tends to die when I stop at a signal. I suspect the needle and seat is gummed up and it just floods out when making a quick stop.
Cleaning the carb and replacing the needle and seat will come next. I have faith that will solve the problem.
Glenn suggested getting rid of electronic ignition. I can't say as I agree with that. Before this problem my car never ran as smooth or started so quick as with the electronic ignition. I suspect he just has too many other gadgets tapping into his power source for the electronic ignition. I am running First Street Ignition from Tulsa OK, and they make a strong point of advising only a dedicated power source so as not to interfere with the electronic ignition.
 
If running a stock Zenith, you would be exhibiting the classic symptom of improper float setting. Others with more Weber experience will chime in soon but it sounds like you're on the right track with an overhaul.

A couple more things to try before carb R&R:
- Run a quart of MMO, ATF or fuel system cleaner thru the tank
- Ensure engine idle speed isn't too low
- Check for vacuum leak around intake manifold and throttle shaft
- Verify you have a constant fuel supply to the carb

Like you, I have nothing but favorable regards for FSI. Good luck and post your resolution.
 
One thing I discovered with the Weber carb, it has a little filter in the fuel inlet area that can become plugged and/or deformed, thereby restricting fuel getting into the float bowl. This caused me all sorts of trouble before I discovered that. Despite the fact that there were 2 filters ahead of this one, it still caught an amazing amount of stuff.
 
I would go into the carb and look at the idle jet. They are really small and easily gummed up. Sitting for a while could have finished off a jet that was just a little restricted. If it was running very well before it was sitting for a long while, most of what is wrong most likely will be fuel, and the carb will be the focal point.
 
Nabco said:
What's wrong with White Castle Tom, since going on a low carb diet a year ago it's one delicacy I miss most :( they are HQ'd here in Columbus too.
Click to expand...

Until two years ago the last White Castle burger was in the early 60's when I went downtown Rochester to see a 3D movie. I'd forgotten how bad they were, or maybe I was so hungry I didn't care, but anyway I had another one two years ago, and that was the nail in the coffin for me. When I'm on a Model A day trip I'll stop at Wendy's or Subway first.:)
 
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