I know that a 350 uses R45TS spark plugs, but ACDelco also makes a Rapid Fire Platinum plug. The Rapid Fire plugs have a higher heat range and cost more. My car runs rich and carbons up the plugs after a couple thousand miles. I think this is due to too big of a carburetor. Would these hotter plugs help with the carbon problem and are they worth the extra money? TIA.

 

What carburetor is on it? IMHO, I would correct the running rich problem rather than trying to Band Aid it.
Also, "back in the day", we would take the car out on the highway to "blow out the carbon", if you get my drift.

 

It has a Holley Street Demon Carburetor and I think it is a 750cfm. It’s probably too big. A new carb is $500. I need new plugs anyway so thought I would try them. I started driving in 1973, so I have blown the carbon out of a lot of different muscle cars. I get your drift.

 

Stock Q-Jet for 79 Vette flowed 750 cfm so, I would deal with the rich problem. Or, try "blowing the carbon out". I always enjoyed doing that!

 

And consider ngk equivalent…

 

The carb isn't too big. If it's running rich it means the carburetor isn't jetted correctly.
Different spark plugs won't fix that. Smaller jets will.

 

And I agree with running NGK's over the Delco's.

 

I have been using the AC Delco Rapid-Fire plugs in my 427 and they work just great. They always last until I pull them and have survived better than other high tech spark plugs that cost several times as much. It is interesting that Lar's also suggested a simple spark plug for applications like mine. No fancy spark plug worked as well as the base spark plug they used in the spark plug test he was involved with.

4-vettes is likely correct in that you need to have someone who knows carburetors to help set it up for you. The best solution for me was to install a Air-Fuel Ratio gauge and that tells you where you need to start working right away. These gauges are not that expensive and are very useful for those with a carburetor. All you do is drive the car while keeping an eye on the A/F ratio. For setting up a carburetor it makes it easier for someone without tons of carburetor experience. I have mine set up so I can use it and then put it back in the garage when not using it.

That much carbon in your engine might indicate a blown power valve which dumps gasoline into the engine. It could also be a standard jetting that might be more of a compromise allowing it to work on a BB as well. You might want to invest in a new gasket set and the various jets that you might need.

Yes, I agree that blowing out the carbon, the old way is really fun. I learned a way that was really simple to do back when I was working on air cooled engines. When the engine is HOT you simply pour a small amount of cool or cold water down the carburetor. This cause a thermal re-action in the cylinder that can break off even the most stubborn carbon. I used to rev the engine with one hand and pour with the other. Do NOT hydro-Lock your engine by pouring more water than is needed, start with teaspoons and move on to tablespoons.

I have never had an engine that carbons up in a couple thousand miles. The jetting might be fine but something is putting way too much fuel into that engine. Again, on most Holley carburetors I would go right to the Power Valve. Power Valves are very easy to damage if the engine backfires or spits. If I were in your shoes I might consider buying the Holley/Demon Calibration Kit for about $125 and use it.

Check your Float height as that also could be the source of the extra fuel that your engine is getting. This is where I found some good information about the Demon 750: https://www.google.com/search?client...h=773&dpr=2.31

Forget your spark plugs and fix that carburetor. If it is more than you are comfortable with then find a mechanic that knows what a carburetor is and have them help, they might have the tools you need to make it easier.

 

Yea I agree but in fact and for real does that really help when we use the fuel in this day and age??
JJ78

 

Before blaming your situation on the carburetor or plugs start looking at the ignition timing and curve.
As far as the carburetor, did you check the float levels?

 

Complete nonsense. A big carb has absolutely nothing to do with the carb running rich. A badly set up and poorly adjusted carb, regardless of size, will run rich. Fix your timing, and then fix the carb issues, and the car will run nice no matter what spark plugs you use. Spark plugs will not cure your timing and carb tuning problems.

Lars

 

My dad bought a new set of champions one time and there was a bad plug so I never buy champions

 

Well that's really helpful Tom.
But believe it or not. You can get a bad one with just about anything nowadays.
However, when it comes to sparkplugs. Some of us install them daily, 6 days a week.
And your not far off the mark. ACCEL is likely the absolute worst. And yes I'm one if those who install spark plugs daily. Followed by, and of course only talking about name brand products here. AC Delco, then Champion.
My best luck with minimal issues is NGK, followed by Nippon Denso.