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Mechanical Help Please (fouled plugs/erratic idle/hard start)


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I ran into an issue the other day when taking the Mach 1 around the block. I just recently got my car operation (full resto) and am troubleshooting and tuning everything now. Prior to this day, the car started, idled, and revved up well, but would get a slight surging effect when I drove it over an idle speed (so far have only made it around the block).

 

During my test drive on this particular day the engine started surging horribly and sounded like it was missing. I limped it back to the house and started diagnosing the issue. It would barely start and had an erratic idle. I assumed I fouled the plugs due to having it miss all the way back to the house (1 block away). I pulled them and, as expected, they were full of carbon. Cleaned and reinstalled the plugs and then tried the restart. I was able to get it started for a few seconds but it was rough at low RPMs and idle. I immediately brought the RPMs up to about 3000. It began to smooth out and run normally at this RPM. I plugged the vacuum advance from the distributor and checked the timing. It was at about 40 total (changed a bit from my initial setting) but could not get the initial because the car would no longer idle. I backed it down to 36 total. I was able to get total set to 36 and the idle then evened out at about 750 (where it was initially set) for a while after I ran it up getting the total timing. The initial was about 14 but hunting slightly. When running it up I had the vacuum gauge hooked up and was steadily getting 55 cm Hg at 4000 RPM.

 

I dropped it down to an idle and let it run for a while. Once it started to cool off the idle started bouncing around between 500-1000 again. I messed with the idle set screws thinking maybe they were too rich and causing the erratic idle. It didn’t make any difference. I then decided maybe there was a vacuum leak somewhere. I plugged the only other two vacuum lines (power booster and PCV to front of carb). I used the started fluid method and came up with nothing, and because I let it cool off a while the idle and low RPM range got worse. It would barely stay running and sounded just as bad as when I started trouble shooting. It still smells and acts like it is running too rich (but I know/think the timing is very close to where it should be).

 

It is now looking like it may be a carb issue (too much fuel at low RPM causing erratic idle and fouling out the plugs). I do have an upgraded cam, but nothing too crazy (see part number and specs below). I took the carb apart and checked the floats. They were at the stock 7/16 setting and everything looked good (all stock settings on the carb). Should I look into changing the springs and possibly the primary jets to restrict fuel flow? Do I need to swap plugs rather than just clean and replace?

 

So as it stands…the car runs like hell, doesn’t want to idle or run at low RPMs, the plugs are fouling from too much fuel and misfires…other than that everything is great! Any advice and technical knowledge would be appreciated.

 

Paul

 

Car specs...

351c bored 30 over

Comp cam: FC 268H-10, Hydraulic Flat Tappet, Adv. Duration 268/268, Lift .494/.494

Edelbrock 650 cfm

Edelbrock Performer Intake for 351c 4v

Stock Ignition system (new distributor and coil)

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My first suspicion is the carb. If I read your post correctly, the car was sitting for a while so there may be a build up inside the fuel metering passages.. Try some seafoam in the gas tank for a while which may clean things out before tearing into the carb itself..

 

All things being equal, mechanical items don't usually change after sitting for a while..

The person who says it cannot be done should not interrupt the person doing it. 

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Gunk in the fuel line may have gotten into the float needle, holding it open, and causing too high of a fuel level, resulting in a too rich condition and flooding. There may also be something loose internally in the carburetor, new doesn't mean it was assembled correctly.

 

 

“If you can't explain it simply, you don't understand it well enough.”

--Albert Einstein

 

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Be careful spraying starting fluid on the engine while running. It is very flammable I would use carb cleaner, less flammable, less chance of fire from spark from a bad plug wire.

Double check your plug wires since you had the plugs out again. Cleaning used plugs is just as good as new unless they are burnt.

I would take your gas line loose up near the carb and crank the engine over and catch the gas in a glass container and see if you see any trash coming through. Like stated might have got some trash in carb.. Hope you did put new filter on.

When a man is in the woods and talks and no women are there is he still wrong??:P

David

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I would check vacuum connections first, then electrical connections in the ignition system. What type of distributor?

 

Use a voltmeter to verify voltage at the ignition coil is 10+ volts.

1971 Mustang

Grabber Lime with black deluxe interior

302 engine with C-4 transmission and 9" rear end with 3.50 gears

 

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Be careful spraying starting fluid on the engine while running. It is very flammable I would use carb cleaner, less flammable, less chance of fire from spark from a bad plug wire.

Double check your plug wires since you had the plugs out again. Cleaning used plugs is just as good as new unless they are burnt.

I would take your gas line loose up near the carb and crank the engine over and catch the gas in a glass container and see if you see any trash coming through. Like stated might have got some trash in carb.. Hope you did put new filter on.

 

I will give that a try. It has all new lines, new tank, new pump, new filter, new plugs, new plug wires. Everything in new. If I pull the carb apart again, where should I be focusing on looking for junk? When I took it apart the first time the bowls were full of fuel and looked clean (but I was not as focused on looking for anything, just checking floats).

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I would check vacuum connections first, then electrical connections in the ignition system. What type of distributor?

 

Use a voltmeter to verify voltage at the ignition coil is 10+ volts.

 

I replaced the coil after this happened and checked the volts, it was at 12.7 or so. Coil wire was checked as well and had steady voltage. All vacuum lines were sealed trying to isolate the problem and I did not find and leaks (they are still plugged). It has the stock distributor with single vac advance (plugged for troubleshooting).

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Check the fuel level in the bowls, make sure it is at the specified level. Check the needle valve(s) for the float(s), make sure there isn't anything in the seats keeping the valve(s) open. Check for debit floating around in the bowls or in the bottoms.

 

 

“If you can't explain it simply, you don't understand it well enough.”

--Albert Einstein

 

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Check the fuel level in the bowls, make sure it is at the specified level. Check the needle valve(s) for the float(s), make sure there isn't anything in the seats keeping the valve(s) open. Check for debit floating around in the bowls or in the bottoms.

 

Took apart the carb again. Fuel level in the bowls was good. Nothing blocking the needle valves (needles and springs looked good). There was a very little amount of debris in the bottom of one bowl. I sucked it out, but doubt that it had anything to do with the issue (very fine and minimal amount, just a few specs). Pumped some fuel into a clear bottle, fuel was clean. When looking down into the intake there was still a bit of standing fuel on the top.

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Did you check the fuel level immediately after running it for a couple of minutes? If so, let it set for a while to see if the fuel level goes down in the bowls. There shouldn't be standing fuel in the intake, so something is either leak in or supplying too much fuel while it is running.

 

You didn't say what carburetor you have. It could be a bad casting with porous metal or something loose, or a blown power valve allowing fuel into the intake.

 

 

“If you can't explain it simply, you don't understand it well enough.”

--Albert Einstein

 

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Did you check the fuel level immediately after running it for a couple of minutes? If so, let it set for a while to see if the fuel level goes down in the bowls. There shouldn't be standing fuel in the intake, so something is either leak in or supplying too much fuel while it is running.

 

You didn't say what carburetor you have. It could be a bad casting with porous metal or something loose, or a blown power valve allowing fuel into the intake.

 

I haven't run if for 24 hours and there is still fuel sitting in the intake, and the bowls are full. But, when I shut it down for good yesterday it was missing and sputtering again so I imagine that has to do with the standing fuel and plugs being fouled again. Not 100% sure, but I don't think it is a leak, I'm thinking maybe just too much is being supplied at idle and low RPMs because that is where the issue is. High RPMs (above 2.5-3.0 seem to be running fine).

 

I have the Edelbrock 650 CFM, electric choke. All the car specs are at the bottom of the initial post.

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Breaker point distributor, I would check the points and condenser. I had a couple of experiences where a bad condenser would make my car run terrible.

1971 Mustang

Grabber Lime with black deluxe interior

302 engine with C-4 transmission and 9" rear end with 3.50 gears

 

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Breaker point distributor, I would check the points and condenser. I had a couple of experiences where a bad condenser would make my car run terrible.

 

I took a look, the points look good. No way to really test the condenser other than swap it. If the condenser was bad wouldn't it be consistent across all RPM ranges?

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Breaker point distributor, I would check the points and condenser. I had a couple of experiences where a bad condenser would make my car run terrible.

 

I took a look, the points look good. No way to really test the condenser other than swap it. If the condenser was bad wouldn't it be consistent across all RPM ranges?

 

I have the original distributor, but...when I got the car the glove box had a bunch of extra condensers and distributor parts which makes me skeptical putting it back on.

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suspect condenser if you are running points.

 

all the new parts are made in china and total garbage, you pretty much have to run electronic ignition now.

if you have a dwell meter hook it up and start the car see how out of wack the dwell is.

 

the points you get today are junk and the condensers you get today are junk.

you have to either find NOS accell or ford from years and years ago cross fingers and hope they are good or you need to go electronic today.

 

----

 

if you still suspect fuel then you might want to run off a 1gallon tank or put a visable fuel filter and see if you are getting a ton of junk out of the tank.

you will want to clean out the carb and see if you can find pieces clogging it up.

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suspect condenser if you are running points.

 

all the new parts are made in china and total garbage, you pretty much have to run electronic ignition now.

if you have a dwell meter hook it up and start the car see how out of wack the dwell is.

 

the points you get today are junk and the condensers you get today are junk.

you have to either find NOS accell or ford from years and years ago cross fingers and hope they are good or you need to go electronic today.

 

----

 

if you still suspect fuel then you might want to run off a 1gallon tank or put a visable fuel filter and see if you are getting a ton of junk out of the tank.

you will want to clean out the carb and see if you can find pieces clogging it up.

I do not have a dwell meter. I do have a NOS set of points, and 2 NOS condensers. The points and 1 condenser are from Parts Master and the other condenser is from Standard Motor Products/Blue Steak.

I don't think fuel contamination is the issue, because I took apart the carb and it was clean. I also pulled the fuel hose and shot some into a container (came out clean). Also all the lines, tank, and filter are brand new.

If it was the distributor/points/condenser would the symptoms change with RPM or be consistent across the board?

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In this era of imported parts, new doesn't necessarily mean good...

 

What type of fuel pump are you running? It sounds a bit like the pump might be pushing fuel past the needle and seat at idle.

 

I though it could also be ignition, but typically if the ignition is weak at idle it will be even worse under load, but you seem to clean up at elevated rpm's.

 

Let us know what you find out.

Matt

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In this era of imported parts, new doesn't necessarily mean good...

 

What type of fuel pump are you running? It sounds a bit like the pump might be pushing fuel past the needle and seat at idle.

 

I though it could also be ignition, but typically if the ignition is weak at idle it will be even worse under load, but you seem to clean up at elevated rpm's.

 

Let us know what you find out.

 

I'm running the stock mechanical fuel pump. Just finished cleaning the plugs and stuck the original distributor on. Getting ready to do a test run and see if things are better.

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If it was the distributor/points/condenser would the symptoms change with RPM or be consistent across the board?

 

it would be all over the place. NOS unless its in the original sealed box from 1971 from ford and never used might be trustworthy. NOS does not mean the part is any good.

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Well, turns out the old distributor does not work. No spark at the plugs, tested with a timing light (that was a waste of about two hours changing it and then changing it back). The new old parts do not fit the new stock style distributor. They have different internals. I'm out of time and patients for today. Will try again tomorrow evening.

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I grew up with nothing but points and condenser. Usually when they get weak they will burn the points. I have had the condenser just die at a red light because the condenser went bad in 289 but always kept new ones in the glove box. The condenser does not have to be for that car as long as you can get it inside the distributor. My 1972 Suzuki motor cycle had one of the three condensers go bad while on a road trip. You can tell which one was bad with the cover off the spark across the points was much brighter flash not blue like a good one. I just got a condenser at parts house and hung in the dist. and got home and got the correct one at motor cycle shop. Yes they have different ratings but about any will work. If I remember correct the one for 351 C with dual points is the same as the 49-53 flathead mount and rating same.

We use to charge them up by letting a spark plug wire arc to the condenser wire and leave them laying around you would know when someone picked it up you would hear then holler, lol.

Crank the car over with cap off and it there is big flash at points condenser is probably bad or weak. If little spark usually ok.

I was luck to find several of the Autolite tune up in a can at a swap meet for $2.00 each. Points, condenser and plugs for $2.00.

I am still thinking something in carb causing the issue. Wish you had another carb to switch out.

When a man is in the woods and talks and no women are there is he still wrong??:P

David

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I grew up with nothing but points and condenser. Usually when they get weak they will burn the points. I have had the condenser just die at a red light because the condenser went bad in 289 but always kept new ones in the glove box. The condenser does not have to be for that car as long as you can get it inside the distributor. My 1972 Suzuki motor cycle had one of the three condensers go bad while on a road trip. You can tell which one was bad with the cover off the spark across the points was much brighter flash not blue like a good one. I just got a condenser at parts house and hung in the dist. and got home and got the correct one at motor cycle shop. Yes they have different ratings but about any will work. If I remember correct the one for 351 C with dual points is the same as the 49-53 flathead mount and rating same.

We use to charge them up by letting a spark plug wire arc to the condenser wire and leave them laying around you would know when someone picked it up you would hear then holler, lol.

Crank the car over with cap off and it there is big flash at points condenser is probably bad or weak. If little spark usually ok.

I was luck to find several of the Autolite tune up in a can at a swap meet for $2.00 each. Points, condenser and plugs for $2.00.

I am still thinking something in carb causing the issue. Wish you had another carb to switch out.

 

Lol, I like the condenser prank. Might have to give that a try. I am also thinking it is more likely in the calibration rather than the ignition. Going to look harder into that today. I have the original carb, but it hasn't run in 25 years so it would take some work getting it operational.

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Question. Why did you swap out the original carb? Did you have this problem before installing the new carb? This issue seems to be fuel starvation and as mentioned before, just because the carb is new doesn't mean it's been assembled correctly. There may be a void in the casting or a crack somewhere inside making it run lean.. Adjusting the idle set screws should always make a difference in the running of the engine. If you turn the screws in all the way, the engine should stall out. If it doesn't, there is a problem with the carb.

 

Have you checked the EGR vale if installed? The diaphram should hold vacuum.. Also inspect the EGR plate for carbon build up which would plug the holes going to the valve.

 

Keep performing the process of elimination so it will bring you to the problem..

The person who says it cannot be done should not interrupt the person doing it. 

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Question. Why did you swap out the original carb? Did you have this problem before installing the new carb? This issue seems to be fuel starvation and as mentioned before, just because the carb is new doesn't mean it's been assembled correctly. There may be a void in the casting or a crack somewhere inside making it run lean.. Adjusting the idle set screws should always make a difference in the running of the engine. If you turn the screws in all the way, the engine should stall out. If it doesn't, there is a problem with the carb.

 

Have you checked the EGR vale if installed? The diaphram should hold vacuum.. Also inspect the EGR plate for carbon build up which would plug the holes going to the valve.

 

Keep performing the process of elimination so it will bring you to the problem..

 

I swapped the original carb and intake during the rebuild. The car was not running when I bought it. The idle set screws do/did make a difference when I was able to get it to idle. It seems to be an excess fuel, not starvation (had loads of carbon on the plugs). No EGR installed.

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