Does changing the plugs really help?

Forget the coil...you don't need it. YES! change the plugs. Worn electrodes means weak spark. Weak spark means incomplete combustion or just as bad, slow combustion. Change the cap, rotor, the wires and the plugs. (old plug wires leak current causing erratic and or weak spark) Have the timing checked and set. All of this should help immensely. Don't forget the air filter; it's a primary cause of poor fuel management. You might just change the fuel filter too. It won't help the gas mileage but it is key to the next step. Get a can of carb spray cleaner and with the motor running, (after you have done all of the above) douche the carb inside and out, especially inside. This will help to clean out the venturi and the exterior air holes. Finally, add a couple of cans of Chevron carb and fuel injector cleaner to the tank...double the recommended dose. After doing all of this you should see a major jump in fuel economy. If not, the carb must be swapped.

I agree with what the other poster wrote, but want to add a tip:

If your carburetor comes with a nitrophyl float (black solid plastic) it is time for a replacement, as these things soak gas after about 5-10 years, causing them to ride lower and thereby raising the fuel level. This causes poor fuel economy and other maladies.

Good luck!

Gerard

If you were to run the car full throttle so it revved to redline (in gear on the street while you are driving) and it doesn't start to miss at higher RPM but just revs up smoothly and then shifts, then IMHO you will gain very little by changing the plugs, wires, coil, or any other ignition parts. Most likely the carb needs work OR that car just naturally gets crappy mileage. Unless you drive it a lot, you could easily spend more trying to "fix" it, then you will spend on extra gas. And your attempts to "fix" it may make it run worse - I found that out the hard way when I bought a early 70's ford at a gvt auction

- it ran great but I figured putt>Hello,

Uhh...are you a mechanic? It doesn't appear that you are, considering this piece of poor advice you're giving out here. Just because you had a bad experience performing a basic maintenance procedure doesn't mean that the next guy will too, and it's plain wrong for you to try to dissuade someone from performing a basic operation just because you had bad luck.

It's a normal thing to change electrical components such as plugs, wires, and cap. If the car runs worse afterwards, then ya did something wrong!

Gerard

I hate to disagree but your unloaded test will prove nothing other than that the valves don't float and that the distributor advances as designed. Only a test under full load will reveal weak spark reliably. I can't say what happened in your case, but changing plugs will never degrade performance unless the new plugs are of the wrong heat range or are gapped incorrectly.

Not fixing things that aren't broke is not poor advice. I offered him a quick and easy diagnostic that will tell him if he has a weak ignition system. If it doesn't miss under the conditions I outlined then his money is better spent looking else where first for his poor mileage problem. You sound like a typical "throw parts at it and hope something works" person, certainly not a mechanic of any skill and you are giving out poor advice.

Just because you had

He's presented no info that suggests he has an ignition system problem.

Never said I didn't accidently crack a plug or damage a plug wire. I was pointing out the wisdom of "if it ain't broke, don't fix it" to someone who is indicating that he has no ignition problem but might have a carb problem.

Do you even read the posts you respond to? How do you equate driving the car on the road and flooring it till it upshifts at full throttle to be an "unloaded test".

Next time take the time to read ALL the post first.

Ummm, he said the plugs were 10 years old and look very worn. I'd say a new set would be the first thing to do and would certainly not constitute throwing parts at it. Just because a car runs worse after YOU tuned it up doesn't mean tune ups are a waste of money. I wonder if your advice "if it ain't broke don't fix it" applies to brakes, tie rod ends, ball joints, etc.? If so it could very well kill someone. Many things need to be fixed before they are broke, both for safety and for saving money. Bob

I have found that many "carburetor" problems are ignition related, and it's always a good idea to do an ignition side tune-up on a car of unknown heritage, like this one.

I happen to have 30 years of auto repair experience, an ASE Master Auto Tech certification, a degree in Mechanical Engineering, and considerable experience helping people with carburetor problems on my carb tuning website.

Your advice of getting out and flooring the car will indeed indicate a severe ignition problem, but it will not indicate worn spark plugs, or marginal wires/cap/rotor, which are things that should be changed on any car acquired without a history.

This guy needs to put new ignition parts in his car before he tackles any other problems. Just because YOU messed up a tune-up doesn't mean that the original poster will too.

Gerard

I tried to be polite but your tone indicates that you were peeved any way. Yes, I read the entire post. A first gear test hardly constitutes a load test. The mechanical advantage provided by first gear is no real test of anything. What it may do is permit something to spin too fast and let loose, definitely not a good idea. To do the test correctly you need the load generated by the upper range of the gears coupled with aerodynamic drag to indicate the type of insidious spark problems that cause poor fuel mileage. The only way to do that is either with a dyno or an actual highway road test. The former being preferred to the latter. As to the rest of your remarks:

Ten year old ignition parts need replacing. Only when you have a solid baseline can you rule out parallel problems. I didn't mean to step on your toes but your advice, though well intended does not jibe with long established tune-up protocol. Replace old and "QUESTIONABLE" parts first. Tighten all nuts, check for leaking gaskets and vacuum lines, clean everything and then, set all adjustments to factory specs. Then, if the problem persists, start tackling the most probable system first, gradually working your way through everything one system at a time. This takes time and yes, it will take money. However, this is hardly money wasted. If you follow this protocol you will only replace those items that are either past their expected service life or very near the end. This is hardly a waste of money. It's common sense, it's safe and it is far cheaper in the long run than having an "on-the-road" break down.

I regret that you took my post so personally, it was not my intent to offend. But sir, your advice is patently poor.

Now, one more bit of advice, this guy needs to check the PVC valve and the warm air bypass flapper. If the PVC valve is clogged, excessive crankcase gasses may hinder exhaust gas scavenging which can lead to poor fuel economy. Likewise, a non-functioning flapper valve may block cold air from getting to the engine after warm up (not to mention that the smaller diameter intake tube will strangle the engine under load). That will have a negative effect on mileage as well. The truth is, these older model cars have a number of weak spots that can really play havoc with fuel economy. Modern systems, while more high-tech, actually are considerably simpler in operation and have far fewer variables that can get out of adjustment. That's one reason why they are able to deliver so much better performance over the older carbureted systems.

AZGuy wrote in news: snipped-for-privacy@4ax.com:

I read all the post, and you don't know what the hell you're talking about. Please stick to reading posts and learning something about cars before offering advice in the future. The fact that you made a car run worse by performing a simple tuneup disqualifies you from advice giving.

The FIRST thing you do when a car runs poorly and gives bad mileage is change plugs, wires and rotor. There is no way to mess this up unless you're a total moron.

Then you suggest that if things don't improve, maybe the engine gets crap gas mileage anyway. A Mercury Zephyr came stock with a 250 inline six equipped with a single barrel carb. It should get at least 15 MPG, even when loaded down with smog equipment.

People start screwing around with the carb when the carb isn't at fault at all. My experience is that carbs tend to last a long time. When they fail, it's usually a bad accelerator pump, easily fixed. It's very rare for a Ford carb to fail. They are very simple appliances, and anybody who can turn a screwdriver and can read can rebuild one. $200 for a rebuilt is ludicrous. That has "I see a sucker coming" written all over it.

1981 Ford cars usually had carbs, and some early kind of EEC. I would always suspect the ignition first, unless I see some definite indicators pointing toward the carb, like stumbling on acceleration, hard hot starts, etc.

Always check the vacuum advance on the distributor. I think 1981 was too early for a gutless distributor.

Now, if this thing has a 302 in it, it would have the VV carb, and all bets are off. He didn't say it was a V-8, and I'm guessing it's not, just on gut instinct. Rebuilt VVs cost way more than $200.

EVERYONE shut up!

The USUAL sign of worn plugs in an otherwise good engine is erratic miss at cruise and at idle. noticable miss under load comes later in the cycle.

In my experience Replacing worn plugs NEVER results in the improvement (up to

15%) suggested by car parts and spark plug commercials... unless the car was running lousy to start with.

BUT it prevents other problems .... it's only good sense to cahnge worn plugs and wires, otherwise they'll let you down when something else goes weak.

So do that full tuneup... but DO NOT buy cheap plug wires... lots of us here have found that there is real foolishness in using cheap wires.

The post about the bad float sounds like the likely culprit to me...

But these cars never really got good milage anyway

Hi Brian, It looks like all good advice about plugs, wires rotor, 10 yr old oil??hummmm You say the guy had car for 7 years and never changed the plugs... If the car was sitting around a lot how old is the gas? Uses gas like crazy...hummm Well regaping old maybe fouled out plugs won't help. Running an old carb ain't going to perform like it should either. Probably the choke and associated mechanism is gummed up. The whole carb is probably varnished up inside. The cap and rotor probably has moisture from climate changes. Yea, 7~10 years of neglect is what you wrote. The car probably needs it all. The using gas like crazy part..Did that make the plugs better? Or did they get a rich atmosphere in the cylinder, which only HEI can withstand. If nothing else, concentrate on the running rich part, cure the carb problem. G.L. BeeVee

======================== Just spend 8 bucks for plugs and go from there. A fancy coil wont do any good unless your is bad. Make sure your choke is opening all the way when its warmed up too.

after you take the majority advice to change the plugs, wires, rotor and cap, let us know if that fixed you poor gas mileage problem. And what do you mean by "poor"? 10 mpg or 16 mpg or ??? Maybe what you think is poor is actually all you can expect from it in around town driving.