The Stovebolt Site Forums The Shop Area Engine Shop Second set of spark plugs fuel fouled?

I have replaced the spark plugs twice in my 1949 1/2 3100 with a 216 cu.in. Granted the truck has seen very little road time and mean very little. It has sat idling for extended periods of time 30 minutes or so at a time, or until it reached operating temperature, two to three times a week. I used AC Delco R45S plugs which I understand are a hotter plug than the R43's. I have the idle circuit screw set a 1 1/4 turns out from the stop, which I get 20+ in. of vacuum with no variation at idle. Idle set a 475 RPM. Would long periods of idling cause the plugs to fuel foul to the point that the truck would begin to run rough? NO oil residue on the plugs, no carbon ash, just a light black shiny residue on the electrode, ceramic insulator. Truck starts up on the first try, but runs like multiple cylinder misfires on the fouled plugs. Timing set on the BB and 3 more degrees at the distributor base. Any ideas or suggestions?

Tim

What kind of carb?

Rochester "B".

Your carb is running too rich or your gasoline is old.

The carburetor was rebuilt, all spec checked and double checked and operates great with no leaks. The gasoline in non-ethanol 87 octane a month old at 1/2 a tank. Stabil 360 was added to the fuel before adding to the tank. Tank is clean and new and all filters are clean. No residue. If it is rich, do I need to turn the mixture screw into say 3/4 turn from stop? Do I need a smaller main jet? Where to start?

Tim

The main jet won't be a factor at idle. If you want to reach operating temp quickly, slip a piece of sheet metal between the idle speed screw and the carb housing to run the idle to 1,000 RPM or so, and cover half the radiator with a piece of cardboard.
Jerry

Shiny usually means oil consumption.
Spark plug heat range is for all-around use, it's too cold for prolonged idling.

Shiny....not wet or slick with oil. According to the Autolite plug reading guide I have fuel fouled plugs. Black with a glazed look. What would be a hotter plug I could use?

Tim

Fixy,
To add to what panic is saying, too rich will leave black soot that will turn your fingers black. I found that out when my accelerator pump sprung a leak and I had to drive her home in a non-stop hurry (at high idle at stop lights).
Is this 216 a fresh rebuild?
Carl

Just
Quit
Idling

The problem will go away as soon as you start using the engine the way it was designed to be run. Until then, keep a spare set of plugs handy and take the fouled ones to somebody with a bead blaster. I went to the race track with 3 or 4 sets of clean plugs every week, which we used for checking the carb mixture during practice. After the race, I just cleaned 'em all up and re-used them the next week.
Jerry

Carl,

You are correct when you get carbon fouling. Black soot and powdery. Cylinder heat while idling without all the fuel being used will cause a light black glazing on the plugs...slight powdering. Check the Autolite spark plug reading guide. This 216 is not a fresh rebuild. Has 51,000 and some change. Was running great until I changed the oil last week? After I changed the oil it began to misfire after idling for 30 minutes or more.

Jerry,

Thank you for chiming in! JQI sounds like that may be my whole situation. I have 2 sets of new plugs as stand by. Will let you know how it goes. Do you know if AC Delco makes a hotter plug than the R45S just to use while tuning...not driving. Should I turn the idle mixture screw in on the carburetor, say to 3/4 turns from seated? Set at 1 1/4 turns now.

It's just not possible to find a hot enough plug to keep from fouling during extended periods of idling. If you're running at idle speed for more than 10 minutes or so, you're not doing the engine any favors. If you absolutely MUST get to operating temp for some reason other than just admiring the sound of the engine, do it at 1,000-1,500 RPM so you'll be in the midrange or high speed fuel circuit- - - -not idle. Once the engine is tuned, it should be good to go for months, with an occasional 5-minute run just to keep things limbered up. What's the purpose for all the tinkering, anyway?
Jerry

I use AC46X in my yard dog with good results. It never gets on the road and is used only as a winch truck. The plugs are for a straight 8 Buick.

Cletis,

Thank you for the suggestion. Where do you find the AC 46X spark plugs? Looks like they've been discontinued. Tried R46S plugs also and no luck there either.

Tim

Check Ebay- - - -there are dozens of new AC "46" heat range plugs- - - -just pick some with the right thread length. Just DO NOT get out on the road for more than a short trip with a plug that hot.
Jerry

You can buy a spark plug sand blaster for about $25 to clean the plugs. It certainly is cheaper then buying new plugs all the time. Turn the mixture screw in slowly till the engine starts slowing down. Then turn it back just enough to get back to the idle speed it was at. Check the float level in the carb. If it is too low it will run rich. I can't imagine why someone will idle an engine for 30 minutes except in a bad traffic jam.

I was idling the engine as I was tuning, adjusting the valves and getting all the "bugs" out. Thanks I will look into the plug cleaner, but I've heard these plug cleaners can leave blasting media or glass beads in the tight areas of the plugs that are very difficult to remove. Will check the idle mixture screw again with a vacuum gauge and see if I have it a little rich. Float level should be OK as I checked it and double checked it when I rebuilt the carb.

Tim

Use an air blow gun with a needle-sharp nozzle to blow the blast residue out of the plug. I have used bead-blasted plugs on race engines that cost upwards of $10K with no problems, so the old mechanics' tales about cleaned plugs causing problems are about as believable as stories of the Easter bunny, Santa Claus, and honest politicians. I used a piece of 1/4" aluminum plate with 8 14MM holes threaded into it as a holder for blasting, and also for storage in the race day tool box.

A high float level causes a rich mixture- - - -not a low one.
Jerry

A high float level causes a rich mixture- - - -not a low one.
Jerry
[/quote]
Right.I got my wires crossed.
George