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1971 302 C4 Coupe - Light Green Metallic
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Discussion Starter · #1 ·
Plenty of threads here naming the same issue, still couldn’t figure mine out. Sorry if it’s repetitive.

Just finished up installing my rebuilt 302 into my ‘71 coupe. Turned the key yesterday and she started right up with only some minor pops. Car wouldn’t idle and ran pretty rough. Adjusted the timing quite a bit with no progress. I hooked up a vacuum gauge and was getting around 15in, not at idle of course. After searching for vacuum leaks and finding none, I remembered I changed the camshaft…duh. Ford Performance E303. Switched the firing order from the standard 302 to 1-3-7-2-6-5-4-8. Engine ran a million times better. Started up even faster and just sounded much healthier, still wouldn’t idle though. If I let my foot off the gas it dies. The car doesn’t have a tach so I couldn’t tell you the lowest RPM I can get to before it roughens out and dies. Vacuum was around 20-21in with the new firing order. I’ve also got a Pertronix Flame Thrower with the Ignitor II module inside. Haven’t gotten around to changing the coil over so it’s still just a 12V Napa coil. I ALSO haven’t purchased the wiring harness to bypass the resistor wire. I read that it should still run fine, so I gave it a shot.

Would it make sense to blame the resistor wire in this case? Or not having the matching coil for the distributor? I’m going to monkey around with timing and mixture screws tomorrow. Idle mixture screw is exactly where it was before I rebuilt the engine. Figured I’d see if anyone else has more ideas. Thanks in advance.
 

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Use your vacuum gauge and adjust both idle mixture screws. You need to know your RPM. Get a (hand held) tach. At what rpm is is dying?
 

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First, get yourself a good Dial-back timing light with a built-in Tach. Then, you'll know where your initial timing is set snd at what RPM. Your Vac numbers are good. What carb are you running? The mix screws can be adjusted for highest Vac at a prescribed Idle RPM. Your initial timing is probably around 10-12º. Much of this is a guess until you see how to runs on the road. When you state "changing the coil over" what does this mean?
Having a Pertronix, you should be running a switched 12Vs to the red side. Recheck your firing order by tracing from the cap to each corresponding plug.
Ok editing to note, you'r running an Eddy carb. I ran 1 1405 for years.
 

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1971 302 C4 Coupe - Light Green Metallic
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Discussion Starter · #4 ·
Use your vacuum gauge and adjust both idle mixture screws. You need to know your RPM. Get a (hand held) tach. At what rpm is is dying?
I’ll try to run out tomorrow and grab one. Bad snow storm coming so it might have to wait a day or so. I don’t have that great of an ear for rpm’s, it tries to idle and then dies. If i had to give it a wild guess i’d say maybe 600-700.
 

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1971 302 C4 Coupe - Light Green Metallic
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Discussion Starter · #5 ·
First, get yourself a good Dial-back timing light with a built-in Tach. Then, you'll know where your initial timing is set snd at what RPM. Your Vac numbers are good. What carb are you running? The mix screws can be adjusted for highest Vac at a prescribed Idle RPM. Your initial timing is probably around 10-12º. Much of this is a guess until you see how to runs on the road. When you state "changing the coil over" what does this mean?
Having a Pertronix, you should be running a switched 12Vs to the red side. Recheck your firing order by tracing from the cap to each corresponding plug.
I got some brand new 8mm plugs which luckily still have cylinder numbers on each end of each plug. 99% positive the plugs go to the correct cylinder - will double check though. When I say switching the coil over I mean purchasing the Pertronix coil instead of running just a generic auto store coil. Not sure the exact model carb, nothing fancy though. Same 2bbl that came with the car…I plan on switching it over to an Edelbrock 4bbl since I have a Performer Intake. Like I said I haven’t cut the resistor wire out or installed the Pertronix wiring harness, so I’m guessing i’m not getting a full 12v?
 

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You can easily bypass the pink resistor wire without having to cut it. Just get a 14 gauge wire (or 12 gauge if you want to over do it) and attach it to each end of the pink wire, ie by the firewall and by the ignition switch, use Scotch-Locks to attach the jumper. Normally I don’t like using them, but in this case with the single strand nichrome pink wire the Scotch-locks work perfectly and will bite into the resistor wire giving a very good connection.

The current will flow thru jumper since it offers no resistance and not the pink resistance wire giving you full voltage to the coil .

I don’t think that’s your issue, but if you want to try it it’s an effective way to bypass the pink wire without having to cut anything. Also it’s easy to reverse and go back to the stock ignition if and when you want to go back to the stock ignition system ( which is my preference after using Pertronix and MSD for many years),

Z
 

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I got some brand new 8mm plugs which luckily still have cylinder numbers on each end of each plug. 99% positive the plugs go to the correct cylinder - will double check though. When I say switching the coil over I mean purchasing the Pertronix coil instead of running just a generic auto store coil. Not sure the exact model carb, nothing fancy though. Same 2bbl that came with the car…I plan on switching it over to an Edelbrock 4bbl since I have a Performer Intake. Like I said I haven’t cut the resistor wire out or installed the Pertronix wiring harness, so I’m guessing i’m not getting a full 12v?
Get it sorted before throwing a coil at it. The one on there is fine. It's not the source of your engine wanting to die "off idle". I think, you have an adjustment issue in the timing and or carb. The reason I mentioned the firing order, is just for a basic check of easy stuff. Inspect all of the carb linkage, including the choke, this is, if your running a 1406 model carb. Insure the linkage is free from any binding. Is the choke plate closed when cold and fully open when the engine is warm? Basic stuff to check.
 

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Discussion Starter · #8 ·
Get it sorted before throwing a coil at it. The one on there is fine. It's not the source of your engine wanting to die "off idle". I think, you have an adjustment issue in the timing and or carb. The reason I mentioned the firing order, is just for a basic check of easy stuff. Inspect all of the carb linkage, including the choke, this is, if your running a 1406 model carb. Insure the linkage is free from any binding. Is the choke plate closed when cold and fully open when the engine is warm? Basic stuff to check.
I understand what you mean about the basic stuff, sorry if I came across as aggressive lol…been a wicked long day. Choke plate is closed when starting but does begin to open as the engine warms. Carb linkage seems to all be okay, I had to use the spectre throttle cable adapter since the stock one doesn’t work with the performer intake.

You can easily bypass the pink resistor wire without having to cut it. Just get a 14 gauge wire (or 12 gauge if you want to over do it) and attach it to each end of the pink wire, ie by the firewall and by the ignition switch, use Scotch-Locks to attach the jumper. Normally I don’t like using them, but in this case with the single strand nichrome pink wire the Scotch-locks work perfectly and will bite into the resistor wire giving a very good connection.

The current will flow thru jumper since it offers no resistance and not the pink resistance wire giving you full voltage to the coil .

I don’t think that’s your issue, but if you want to try it it’s an effective way to bypass the pink wire without having to cut anything. Also it’s easy to reverse and go back to the stock ignition if and when you want to go back to the stock ignition system ( which is my preference after using Pertronix and MSD for many years),

Z
I’ll most likely do that then, easier and cheaper than buying the relay IMO. You might be right that it isn’t my issue, who knows. Start checking things off the list and I get closer each time! Thanks for the suggestion.
 

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When you checked the engine Vac, was the needle relatively stable at the 20-21 hg? Also, from where did you pull the Vac?
 

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Discussion Starter · #10 ·
When you checked the engine Vac, was the needle relatively stable at the 20-21 hg? Also, from where did you pull the Vac?
Yes, the needle didn’t fluctuate much at all. I unplugged the vacuum advance hose, capped off the distributer, and plugged in the gauge into the carb.
 

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Yes, the needle didn’t fluctuate much at all. I unplugged the vacuum advance hose, capped off the distributer, and plugged in the gauge into the carb.
Ok good. When you say you need to keep the RPMs hight to keep the engine from stalling. How are you applying the accelerator, that is, are you using a constant pressure or feathering it, so to speak. Am thinking along the lines of the carb's internal functions. If the fuel bowl has debris in it, it will clog the idle passages and prevent a smooth flow of fuel through them, thus, the engine will be starved and die.
 

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Discussion Starter · #12 ·
Ok good. When you say you need to keep the RPMs hight to keep the engine from stalling. How are you applying the accelerator, that is, are you using a constant pressure or feathering it, so to speak. Am thinking along the lines of the carb's internal functions. If the fuel bowl has debris in it, it will clog the idle passages and prevent a smooth flow of fuel through them, thus, the engine will be starved and die.
I can get the engine to run very smoothly, it just doesn’t survive without the throttle open. When I was monkeying around with the timing - spinning the dist until I had best vacuum - I had the throttle held at the lowest rpm I could. Hopefully I’ll have a number for you once I can grab a tach. No feathering just keeping the throttle at the same spot. Revs up just fine as well.
 

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I can get the engine to run very smoothly, it just doesn’t survive without the throttle open. When I was monkeying around with the timing - spinning the dist until I had best vacuum - I had the throttle held at the lowest rpm I could. Hopefully I’ll have a number for you once I can grab a tach. No feathering just keeping the throttle at the same spot. Revs up just fine as well.
Ok, dig into the carb. I'm thinking it needs a good cleaning. It's not picking up fuel. By your throttle opening, it seems to be running off the transition circuit. I'm not familiar with your two barrel, but, it's not that complicated. This will be good practice for when you get that 4 barrel and it needs service.
 

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Let's see a pic of your carb setup. Did you try to raise the idle speed with the screw on the throttle, so that it would stay running on it's own?

You can power the Ignitor module itself with a full 12V off the red w/yellow hash mark connector by the firewall, it was originally used for the the throttle position solenoid and is hot in Start and Run. Leave the factory (+) wire on your coil and see if that helps the situation. If not, then it's probably time for a carb rebuild.
 

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Almost certainly not an ignition issue. I'd be looking at the carburetor's idle circuit first.
 

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Discussion Starter · #16 ·
Okay, I took some pictures of the carb setup. I took apart the throttle linkage to put the new spectre bracket on…I was manually pressing the carburetor before anyways. Haven’t gotten around to messing with the mixture screw as I’ve been doing a job shadow all day.

I posted a thread a while back when I first got the car, some weird popping and backfiring in the higher RPM’s. Some suggested that the mixture was too lean. A pcv vacuum leak ended up being the culprit but it’s still possible that the carb isn’t adjusted properly. Figured i’d mention that here are the pics…
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Don’t mind the messy wires…eventually going to be cleaned up.
 

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Your hot air choke isn't hooked up. I don't see any wires coming off the thermostat so it doesn't look like it's been converted to electric choke. You need to get this hooked up and the choke adjustments done. When the car is cold the choke should be closed and the high speed idle set by the high speed idle cam, once the engine is sufficiently warm when you hit the gas, the choke thermostat fully opens the choke and takes the throttle blades off the high idle cam and then its running on your idle adjust screw. When the motor is cold, it won't generally want to run on the normal idle setting until it's up to temp. I would make sure your timing is set correctly, then hook up the choke and do the choke adjustments. choke adjustments need to be done with the motor cold.

If you don't have the parts to hook up the choke right now, loosen the thermostat and rotate it so the blades stay open on their own. In the mean time you will have to manually feather the gas or sit there holding the motor at 1200 rpm or so until the motor is warm enough to idle on its own. Once it's at operating temperature, then I would start adjusting the carb. If you aren't used to old carbureted motors and have only driven fuel injection, you may be expecting it to fire up and idle on its own from a cold condition. These old motors will do that, but only if they are adjusted correctly and right now it seems your choke isn't even hooked up. Typically when all is set, the start sequence is 3 pumps of the gas then fire it up. when the motors cold you have to push the pedal to set the choke initially.

Car Motor vehicle Vehicle Steering part Hood


Idle screw
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Discussion Starter · #18 ·
Your hot air choke isn't hooked up. I don't see any wires coming off the thermostat so it doesn't look like it's been converted to electric choke. You need to get this hooked up and the choke adjustments done. When the car is cold the choke should be closed and the high speed idle set by the high speed idle cam, once the engine is sufficiently warm when you hit the gas, the choke thermostat fully opens the choke and takes the throttle blades off the high idle cam and then its running on your idle adjust screw. When the motor is cold, it won't generally want to run on the normal idle setting until it's up to temp. I would make sure your timing is set correctly, then hook up the choke and do the choke adjustments. choke adjustments need to be done with the motor cold.

If you don't have the parts to hook up the choke right now, loosen the thermostat and rotate it so the blades stay open on their own. In the mean time you will have to manually feather the gas or sit there holding the motor at 1200 rpm or so until the motor is warm enough to idle on its own. Once it's at operating temperature, then I would start adjusting the carb. If you aren't used to old carbureted motors and have only driven fuel injection, you may be expecting it to fire up and idle on its own from a cold condition. These old motors will do that, but only if they are adjusted correctly and right now it seems your choke isn't even hooked up. Typically when all is set, the start sequence is 3 pumps of the gas then fire it up. when the motors cold you have to push the pedal to set the choke initially.

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Idle screw View attachment 823974
Wow, thanks for taking the time to explain that. Do you know of any good YouTube videos that visually show hooking up the hot air choke? Not trying to sound lazy, I just know it’s hit or miss with some things. It was a bit of a change going from a modern car to this older car, I got used to it eventually. Now i’ve gotta just learn more about them!

I know before I pulled the engine, when I gave the cold engine a pump of gas to start it, I could hear the choke plate slam shut. When I rev the engine now, it flutters open slightly and seems to open wider the longer I run the engine.
 

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Get yourself a good Shop manual. It'll pay for itself.
 

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Here check it out, I had essentially the exact same carb sitting on my shelf off my 70 mustang 302.

These two screws are the air-fuel adjustment screws. They need to be adjusted for a healthy idle. Tighten them until the lightly stop wanting to turn, then back them out 2 1/2 turns.
Motor vehicle Auto part Gas Engineering Machine



On yours you have a vacuum cap sealing the float bowl vent. You need to remove it otherwise you're going to run into issue since the float bowl can't vent properly. Here's how mine is set up. It appears its running into the air intake.

Yours
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MINE
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Here's what the choke looks like when the motor is cold, its springs shut to this position
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Mine was converted to electric choke at some point in its life.
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This adjustment here sets the choke gap when the choke is closed when the motor is cold. There's a specific measurement for the gap that's set with feeler gages. the setting would be in the carb rebuild kit or the repair manual. I don't have it handy.

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Underneath the choke thermostat housing you will find the fast idle adjust screw. That's the Blue Arrow. You can see it is touching the fast idle cam, highlighted with the green arrow.

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I usually set this when the engine is dead cold, I crank the screw in and fire the engine. It will generally be idling high, then without touching the gas, I will tighten or loosen this screw to obtain around 1200 RPM idle speed. This idle speed is only when the car is warming up. As the car warms up the choke thermostat spring heats up and wants to twist the choke open, it can't because the fast idle screw is sitting on the fast idle cam. the idle will not come down until the engine is warm enough and you hit the gas pedal. In a modern fuel injected car, you've probably notice when you first start it when its cold it idles high for a little while. This is the mechanical method for the same process.
 

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