How often should you replace spark plugs? Lately the roadster(327 Chev engine) has been neglected and I have also noticed an increase in fuel consumption. I will be doing a bit of maintenance on the roadster and that will include rebuilding the carburetors (Rochestor 2G's) to replace all the gaskets and other parts that suffer from the effects of unleaded fuel. So then I thought about plugs and realized that they hadn't been cleaned or replaced in probably 3 years. Pulled one and very black. I have a local guy who has a sand cleaning machine for plugs and he can do all 8 for say $15 or buy new ones for about $40 for 8. I think I will buy new. How significant are the plugs in relation to fuel consumption. I would guess that a dirty plug will not operate efficiently and could contribute to higher fuel consumption. While on that subject how does the fuel/air idle settings affect fuel consumption once you are at operating speed? I set mine and the vacuum gauge shows that the engine is running in the correct range. Can poorly set idle screws also affect fuel consumption?
If the plugs are black the car is running rich. You should figure out why and fix it. I blast plugs with an old plug blaster I bought from a going out of business gas station years ago. Cleans them up like new. Are you running a points ignition? If so clean and file the points or replace then adjust the gap.
They are clean but the blasting makes the porcelain is rougher than stock and it will attract deposits. I've found the plugs in my Y-Block stay a lot cleaner with today's fuel. I agree with the rich problem. Fix it. Good luck.
Fuel pressure, float level, choke setting, condenser in dist are things to consider and not overlook too.
Correct, fix your rich fuel problem. DON'T waste your time sand blasting spark plugs. That is a 1950's fix. One needs to understand how a spark plug works to understand why you shouldn't waste your time performing this "trick" that time and intelligence has LONG since passed by. Even low air pressure, pits the porcelain (a BAD thing), rounds of the center electrode edges (a BAD thing), and rounds off the ground electrode edges (a BAD thing). All three of the above situations will degrade the plug is "supposed" to work. And, this "fix" won't last long before it needs cleaning...again. It will continue to degrade the way the plug works every time it's done. Suck it up, get out your wallet, and buy a fresh set of spark plugs. Your engine will appreciate it. Mike
Yes new plugs and carburetors rebuilt is the plan. I have electronic ignition so no points or condenser.
I think the running rich might be because the front and rear carbs have been letting some fuel in even when they are not activated by the linkage. Normally the middle carb is the only one operating and front and rear only come on when full throttle activated. However sometimes the front and rear ones leak extra fuel in and I think the rebuild on all 3 will clear up some of this.
It might be worth while to take a look under the dist cap on that electronic ignition as well. The terminals in the cap and on the rotor also get pitted and build up carbon, which can cause issues. With new plugs, rebuild carbs, fresh cap & rotor and maybe a set of plug wires, your car will run like new! You will probably get a speeding ticket because of the increased performance. Gene
I'd agree that the excess gas is a large part of the problem. Back to the original question, back in the 60's when I started doing tune ups we figure 10,000 miles was about the norm between tune ups for most rigs. Some went more, some went less and some went a lot more if the had all road miles. Throw in a fuel system that runs rich, the plugs aren't going to last as long. Have only short driving trips around town where the engine never really warms up they don't last as long. Those plug sand blaster/cleaners usually got used on plugs of the cars that never got past the city limits and never saw highways speeds. Every few months they would carbon up to the point they would barely run. A ten mile blast up the highway and back at the speed limit or above after pouring a can of top oil or atf down the carb would probably have done a better job. Thing was when you pulled and sand blasted a set of plugs it was all labor and on many of those cars you cleaned the plugs every three or four months on a continual repeat business..
Idle mixture screws as their name implies are mostly for idle. But they have a big affect how it runs just off idle where a whole lot of driving is done so they need to be set right. The fuel mixture for highway speeds is handled by the jets. You'll have to get into spark plug reading, it's more involved than people think and tricky with today's gas. When the carburetor is adjusted and jetted correctly they should run pretty clean, because of modern unleaded fuel.
$40 is a lot for spark plugs, I get NGK plugs for my car on eBay for less than 1/2 that. Sand blasting, I would go with that while you are sorting the mixture issues out. Even $15 for that is quite a lot and a big down payment on a set of plugs. I give them to my son who works in a machine shop.
If the plugs are black then most likely the carb is way out of adjustment. I'd hold off on new plugs for now and dial in the carburetor till those plugs are burning clean. The big thing about new plugs is the electrodes have nice crisp clean sharp edges. It takes a lot more voltage to fire a worn plug. If they are fouled badly there will probably be some misfires, clean burning plugs don't do that.
This is Australia and EVERYTHING is expensive. I could check on EBay but the parts shop is only 1km away.
I have ordered 3 carb rebuild kits from Quadrajet in USA and should be here in a week. Checked on EBay(Aust) and the plugs range in price from $35 to $60!!! for 8 plugs. I will head down to Super Cheap Autos for mine and have them on hand. I agree that the carbs need attention first and then replace the plugs.
I would guess somewhere between 20 and 50 thousand miles. I have cleaned (glass beaded) a lot of spark plugs over the years, and haven't noticed a problem with them. Just blast the minimum amount required to remove deposits, and primarily aim the blast straight at the end so as to minimize hitting the centre electrode. I made up a little jig which is a piece of 1/4" x 2" aluminium strip with four 14mm holes tapped in it. I thread in the plugs until they are flush on the other end in order to minimise overspray of the glass beads. If the plugs are at all oily, I first clean them by soaking them in a small container of gasoline overnight, then let air dry or blow off.
the end carbs "dribbling" on a progressive 3x2 system can be a problem when the end carbs are almost never used. I have the same problems on my 55 so I make sure to use the end carbs every time I drive it. I think a guy could get by with setting the float levels on the end carbs maybe 1/8 " or so lower than stock. And I hate to even mention this on a hot rod site for fear that I will be run out of town on a rail, but if you typically don't use the secondarys just dummy up the end carbs so you don't have to worry about the dribbling problem. Also what is the ctr carb jetted at? maybe try jets 1 or 2 numbers smaller. You will be able to tell right away if it is too lean as it will surge at freeway cruising speeds.... good luck
this The plugs don't turn black because they're old...they turn black because of too much fuel. Usually this happens under certain conditions, such as idle, or when the choke is on, or something. Fix the carbs, take it for a long drive, check the plugs again.
Get rid of those hokey chokey little aircleaners and start again. They are like having the choke on full time of worse. Can't tune it properly with those things in the way.
On the 2G, 2GC rochesters a float check is always in order. Leaking float always drops fuel no matter the drop setting. Just went thru this. Also the ends should be totally sealed, no vacuum leaks. A really good check for all this is to pull the ends, block off the manifold, and see how it runs on just the center. You might find you don't have a fuel rich problem.
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