Fouled plug

[Ron R.]

After running engine in garage for about 20 minutes idling between 1000-1500 rpm's, I pulled a plug out for inspection since they seem to be fouling prematurely. As I suspected the plug. I checked was black with carbon.
The plug I'm using is a Accel short plug(due to headers) 576S. Engine is a built up 301, carb is 4776S, stock dist.,compression between 160-170, dwell about 35 degrees,
Any suggestions what else to check or is the plug too cold for this engine.

[Al E.]

Re: Fouled plug

Hey Ron.. my experience if its black ****t.. then its burning too rich... Carb needs to be dialed a qrt turn on the fuel mixture. Keep track of each turn until you find the right mix. That's all with respect that your valves are seating flush.
It had a rebuilt Qjet but i swapped it for a carb i found off a camaro. It was perfect. END RESULT my Qjet wasn't built right.

[Steven B.]

Re: Fouled plug

Definitely sounds rich. If you're getting a bit of black exhaust, that would be consistent with a rich condition. You may have the idle mixture screws off a bit, but at 1000-1500 rpm, I believe the throttle plates should be uncovering the transfer slots. The nice thing about the 4776 is the external float adjustment and sight plugs. You may need to lower the fuel level slightly and see if this clears things up. You also might want to go with a little hotter plug. Also as an afterthought, I've had choke plates that weren't all the way open with a mechanical choke because of adjustments. Do you know what size the jets are? I'm sure others will have suggestions.
Good luck

Steve

[Jim D.]

Re: Fouled plug

As you know, you have a 600 CFM double pumper. They are not a street carb. Everything about them, from the air bleeds to the jetting is designed to run rich for track use. Your best bet is to start with a correct carb., one designed for street use.

[Ron R.]

Re: Fouled plug

The carb was just rebuilt by a reputable carb guy, based on the engines specs he replaced jets with numbers 67 and 74, also replaced power valve with a 3.5 value. The idle mixture screws were turned out 1.5 turns, maybe I need to turn screws in to 1 turn out. Will also use a vacuum gauge to get the optimum setting on screws. Another problem may have been the chock was open too far when engine was still cold. Thoughts?

[Steven B.]

Re: Fouled plug

The power valve seems a bit low. I would have thought something around 6.5 would have been what that carburetor came with out of the box, but I've been wrong before.

Steve

[Timothy B.]

Re: Fouled plug

As you know, you have a 600 CFM double pumper. They are not a street carb. Everything about them, from the air bleeds to the jetting is designed to run rich for track use. Your best bet is to start with a correct carb., one designed for street use.

I agree with Jim, the double pumper is rich but if you are so inclined it can be leaned. In the 1000-2500 rpm range you are running on the idle circuit, the power valve and main jet have no effect on the the A/F mixture at those speeds. Idle circuit A/F tuning involves the idle feed restriction and idle air bleed and usually takes a skilled hand unless you have lots of patience but it can be very rewarding as it's a great learning experience.

Keep in mind lots of garage idling time without engine loads from being driven can cause the condition you describe.

[Rick A.]

Re: Fouled plug

agree with Mr. Blanchard

[Joe C.]

Re: Fouled plug

Your plug cross references to a R45TS, which is the proper heat range. Are all 8 plugs black and sooty? What kind of ignition system and coil are you using?

3.5 PV comes in later than 6.5 so if anything it would starve his engine of fuel under a load.
In other words, it has nothing to do with his black plug situation.
Jets are perfect and the fact that it's a DP shouldn't foul plugs. Take it from me......I have a 750 DP and don't foul plugs.

But that MIGHT not be the OPs problem. IF he's fouling only ONE plug......... it's something else.

[Frank D.]

Re: Fouled plug

Holley describes the dbl pumper for "hot" street use on lightweight cars with manual trannys or autos with a high stall rate and low rear gears.
I ran a 650 dbl pumper commuting between Norfolk, VA and Leonardtown, MD every weekend for two years - never touched it. Commuted in Wash DC traffic too for a while.

Sounds like your engine is "built" so that is a consideration. Pull all the plugs and do an analysis before randomly swapping parts... Just my opinion...

[Ron R.]

Re: Fouled plug

All plugs are fouling, the coil is an Accel super stock #8140 and the dist. Is stock.
Some specs on the engine are TRW pistons 12.5 to 1, crower solid cam 5.25 lift, 300 duration, engine is 301 balanced and blue printed.
plugs are black with carbon only.
Really anxious to get this tanker back on the road.

[Joe C.]

Re: Fouled plug

All plugs are fouling, the coil is an Accel super stock #8140 and the dist. Is stock.
Some specs on the engine are TRW pistons 12.5 to 1, crower solid cam 5.25 lift, 300 duration, engine is 301 balanced and blue printed.
plugs are black with carbon only.
Really anxious to get this tanker back on the road.

Jury is OUT on whether or not your coil needs a ballast resistor but, judging by the fact that it is only 1.4 ohms primary resistance, I would say that it should not have one and won't develop enough energy if run with one. The reason I say this are twofold................one, is that most coils that require ballast are around 3 ohms, primary..............and those that do not use an external ballast are around 1 - 1.5 ohms.

So, are you using any external ballast?

That being said, if you run your ACCEL coil with ballast removed or bypassed, you will risk burning points more quickly than normal. I suggest bypassing it, cleaning your plugs and road testing it. If the problem clears then you have two choices, ONE, replace your coil with a low performance coil requiring external ballast. Or TWO: your engine sounds like a potent build, and with that much cam you would be wise to keep your High energy coil, upgrade to a MSD or Pertronix ignition system and use 8.5/9 mm plug wires.