Any thoughts on these spark plugs?

[Flash_Harry]

From a recently rebuilt engine which now has about 2500 miles from startup. It's been running pretty well, but has been stumbling occasionally. I pulled the plugs when it was hard starting, and found all four pretty black. #1 and #2 weren't too bad, #4 was pretty black, but #3 is black, with heavy buildup outside and down inside the insulator. The last longish drive was 116 miles, and it disappeared about a pint of oil - now using Valvoline VR1 20W-50.

Any ideas as to cause, and/or what could be done?
Harry

 

[Keoke]

You did not state what vendors plug you are using. However, it may be they are not the correct heat range.

 

[JPSmit]

From a recently rebuilt engine which now has about 2500 miles from startup. It's been running pretty well, but has been stumbling occasionally. I pulled the plugs when it was hard starting, and found all four pretty black. #1 and #2 weren't too bad, #4 was pretty black, but #3 is black, with heavy buildup outside and down inside the insulator. The last longish drive was 116 miles, and it disappeared about a pint of oil - now using Valvoline VR1 20W-50.

Any ideas as to cause, and/or what could be done?
Harry

View attachment 24438

Those look like you are.running really rich. Can you lean up the carbs?

 

[DrEntropy]

Induction setup? The difference between 3 and 4 is kinda stark.

My WAG is guide clearances or stem seals.

If this is a B-series engine, the #3 cylinder is usually the hottest, too. It shouldn't be that coked-up.

Is the ignition system up to snuff?

 

[Flash_Harry]

Thanks for the replies, guys.

Plugs are NGK with 2500 miles - correct range according to rebuilder.
We've been trying to get the carbs tweaked, but it's been a struggle. Rebuilt HIF4's.
Ignition is rebuilt 25D with points - also 2500 miles. New plug wires, too.
Forgot to mention, last trip of 116 miles, got 18 mpg - with 5-speed tranny.

 

[LarryK]

What grade of fuel?

 

[PAUL161]

You should be getting around 30 MPG! Were the carbs professionally rebuilt, or a home brew fix up? You've got carb problems, especially the back one. If they were professionally rebuilt, send them back and have them go through them again. SU carbs are about the most basic carburettor ever made for an automobile. There's nothing wrong or unusual about HIF-4 carbs, but if they arent set up right, they won't work right. PJ

 

[AN5Sprite]

My initial thought without reading the text was; Oil fouling, the pic isn't great but #2 looks looks shiny. After reading that you're consuming oil... If it were me, I'd do compression and leak-down tests for a little more info. Don't let the fact that the motor was recently rebuilt factor into the trouble shooting process. (that's my best .02)

 

[Hap Waldrop]

Harry, how are you doing. The fuel mixture is too rich, move the jets about .020" up toward the bridge from where they are now, and install a new set of NGK BR6ES plugs, unless you have spark plug blaster to clean them with, in which case they could be reused, gap them at about .030". Call me if you have any questions.


When I first got my 67 GT from Tony, same deal, I was getting less 20 miles to the gallon, I end up leaning the carbs until I got to the point of changing to the next leaner neeelde, I ended up back with stock needle and .020" leaner than the stock setting, the car then cranked, and ran better, and the mpg went up to about 30 mpg. No two cars are the same when it comes to fuel mixture, one likes one thing, one like another, don't be afarid to change mixture and try things, I normally work in .010"-.020" increments, if I get to a point where then needle setting is less than .050" from the bridge, then I go to the next leaner needle. I like to pull dashpot (three screws), spring and piston, and measure the jet's postion in relationship to the bridge with the end of dial caliper, if you don't have a dial caliper, it's great tool for this purpsoe and you can get one at Harbor Frieght for about $20.

 

[Flash_Harry]

Thanks all. I will try checking and testing and adjusting to see if we can get this straightened out. Had planned to put in new plugs, and see if we can get the carbs leaned out some more. Right now it will only accept 93 octane gas. As one buddy says: "Ya gotta love em!"
Harry