Technical Small block Chevy, needing spark plug advise. Thanks!

I have a 350 Chevy and I'm having trouble with fouling spark plugs (NGK G-Power Platinum Plug Number UR4GP Spark Plugs, gapped at .035) I've tried other plugs too. New build. Standard bore 350, 305 cast iron heads, ported and polished, Holley intake, ProForm 650 double pumper carb, (came with #70 main jets, now has #67 main jets), 93 octane pump gas, doesn't ping, starts easy, shuts off without running on, headers, cam (SUM-1784, 2500-6000 rpm, intake, exhaust duration, 228, intake, exhaust valve lift, 0.480 in), stock vacuum advance distributor with a Pertronix ignitor in it, Bosch blue coil. Timing is manifold vacuum, timing is set at 42 degrees. It runs great, best running small block I've ever built, but fouls plugs, fairly quickly too. Seems to do it at idle. Spark plugs are black and sooty. It's in a early 60's Chevy truck, 2800 stall, 700R4 ******, 373 rear gears, 29" tall ***es. Not sure what other info to give. Oh, the choke isn't stuck shut, it opens all the way. Thanks for the help.

 

Have you tried AC R45TS plugs?

Tell us about how you adjusted the idle mixture

 

I had the same problem when I was a junior in high school.
The rings hadn’t seated yet .
I had used double Moly rings,,,,,,I didn’t know any better .
They would never seat,,,,I had to tear it down and switch to a regular ring .
After about a 1000 miles I literally felt them seat one day,,,,,,,man it was great after that .
Perhaps your rings haven’t seated yet ?

Tommy

 

It would help to see the plugs, does the carb have a power valve ? the float levels could be to high also.

 

Those Plugs are off topic! What about AC Delco Rapid Fire or just plain old R45TS or TSX if you want to run a bigger gap.

 

Squirrel, no I haven't tried those plugs. Idle screws are out 3/4 of a turn.

 

I'm with squirrel, ac plugs and also agree about ring break in along with checking carb for over rich condition.

.

 

Or try a UR4 NGK, I'm not a fan of platinum or iridium plugs in carbed cars, they work ok but don't get the range they're advertised, cost more and seem to be more susceptible to a slightly off mixture.

 

can you lean it out some, without making it stumble or stall?

 

With the electronic ignition, you could probably open the plug gap to .040 or .045. What does Pertronix recommend?

 

I don't want you to think what I have to suggest is the answer. But maybe?
That plug lacks the hot snap of a flat tipped plug. With the head design, I think the gas isn't burning hot enough at idle.

 

1oldtimer, it has those plugs in it now, NGK UR4. I've never used them before. I have used NGK racing plug R5674-6 and they fouled too.

 

pprather, I'm getting conflicting info on the plug gap. I'll have to research it more. I'll go to the Pertronix site later and see what I can find. I might email petronix, I've done that before and had good results. They're the one's that suggested the bosch blue coil.

 

This is from the Pertronix web site, (We recommend that the gap be increased a maximum of .007" over the factory specification.) So you are right, I should be able to open the spark plug gap up to .040 or .045.

 

I ordered the AC R45TS plugs, per Squirrel. I don't think the 650 is to big for it, is it? I'm wondering if a 600 would be better.

 

With the idle mixture screws only out 3/4 turn I wonder if a float (or both) might be set too high?

 

Learn how to use a vacuum gauge to dial in the carb...

 

Is your 42 degrees of timing with or without vacuum advance hooked up? How much vacuum advance? What RPM is the timing all in at? Agree with R45TS plugs.

 

Could your jetting still be too rich-causing the fouling?

 

In my experience (on twostrokes mostly) regularly fouling plugs comes from one of two causes: Too much fuel (usually idle/low load situations) or too cold plugs.
Both make the plugs run too cold in low load situations, carbon builds up on the plugs while they don't get hot enough to self clean and burn it off.

I'd lean it out and see how it reacts. And if you're cheap, your fouled plugs can probably be brought back to life with a propane torch. (Although running platinum plugs implies you aren't.)

 

The idle mixture is adjusted with screws, the jets should not affect it. Play with them....you want to set them as lean as you can, but still have it idle OK and not hesitate when you open the throttle. Holly type carbs usually have the adjustment somewhere less than one turn, as they have a rather blunt tip, not a long taper on them.

The "S" on the end of the AC part number means it has an extended tip, which helps prevent fouling at idle.

 

Right away I was thinking power valve. It could be faulty and dumping on you somewhere between idle, driving and WFO. I like em about 4 to 5 on most performance get ups. I also really like Autolite plugs in hot rod motors. I was talked into NGK, "...never anything but a Champion!" and others too. But Autolites worked in every hopped up gig I ever had. I ran the same fkn plugs in my bracket racer all year. Never changed em. I used em on N2O apps too. All my resto motor tunes get Autolite. And NOT Motorcraft, I dunno why. There's only been 2 vehicles in my life that liked NGK, a high zoot 800cc Mach Z and my old 72 Harley FX. The HD would foul Champions in 100 miles. My racer ate plugs in the 5th round. The switch to Autolite in the cars was magic. Nitrous guys used to be quite adamant about it. Hey, let us know.

Quick edit, yes open the gap. Biggest gap possible without misfires gives the best performance.

 

Thanks for all the advice. The NGK plugs in it now are not happy. Waiting on the AcDelcos to get here from Summit. I have #67 jets in it, and I'm going to put #66 jets in it. The NGK plugs lasted less than 50 miles of in town driving. Drove it around yesterday and it ran great. Noticed on the way home it was starting to run bad. Drove it to a cruise night last night and it was running worse. Funny thing is, even with the fouled plugs you can stuff your foot in it and it lights up the rear tires. I'm really happy with the way it runs, just need to figure this out.

 

Have you put a vacuum gauge on it to see what the vacuum is at idle? That's the first thing I'd do, and while the gauge is connected I'd adjust the idle/air screws to obtain the highest vacuum possible.

 

If all the plugs are Fouled - I think of blown Power Valve and/or too rich idle settings.

 

427 Sleeper, the 42 degrees is with vacuum hooked up.

 

That is wrong,it should be without vacuum advance.

 

42 is about right with vacuum connected...but it would be good to know what the total timing is, without vacuum connected, also.

 

I was dealing with same issue. Turned out my pcv was in one of the rubber grommets with a slot. Installed a metal one and problem disappeared.

 

I didn’t know that about the “S”. I was always told that the “TS” was for a tapered seat plug rather than the older metal gasketed type.