Hello, from NYC. 73 Mach 1

[3pedals]

Bought a 73 Q code, 4 speed manual a month ago. Been wanting a 71-73 for over 20 years. This one is very clean overall, but not idling great. Coughs through the carb sometimes, has done a few loud backfires while driving, sometimes will die at idle on its own, has done a little bit of dieseling after shutdown after running for a while.
I haven't had a carb car for a long time so working through issues is new to me. I've got a carb rebuild kit (road demon) and planning to clean it, check condition of all the spark plugs, measure vacuum, etc, and see if I can get it running nice myself. Wish me luck!

 

[tpj71mach]

Welcome from Chicago! I wish I could offer a suggestion, but I am new to Mustangs and it's all still a bit foreign for me. There are a lot of very knowledgeable people on this forum, I have learned a lot so far from them. I am sure someone will have some suggestions on what to check.

 

[Sheriff41]

Welcome and howdy from Texas! Great looking Mach 1! I had a yellow 73 Mach 1 back in the 80s that looked very much like yours. Yellow on black is one of my favorite color combos on these cars.

Since the car is new to you, I would suggest giving it a complete tune up so you know everything - plugs, points, condenser, plug wires, filters, timing, carb tune, no vacuum leaks, etc. - is correct and functioning right. Also, make sure your idle RPMs aren't set too high.

 

[PoFoMoCo]

Hey NYC! Another big welcome from Texas. That’s a beautiful car…. yellow & black is a show stopper. The car sure looks well cared for. What’s the back story on the car, where it came from and how you found it?!?

You are definitely in the right place for help, these members are on top of their game.

Good Luck!

 

[Idaho Chris]

Welcome from North Idaho. Nice looking car!

 

[Mac]

Welcome from N.E. Ohio. As far as carb issues, also consider looking at your timing and over time the rubber in your harmonic balancer breaks down so timing marks are not always accurate. One other item to look at is your fuel filter may have build up in it.

 

[3pedals]

Welcome and howdy from Texas! Great looking Mach 1! I had a yellow 73 Mach 1 back in the 80s that looked very much like yours. Yellow on black is one of my favorite color combos on these cars.

Since the car is new to you, I would suggest giving it a complete tune up so you know everything - plugs, points, condenser, plug wires, filters, timing, carb tune, no vacuum leaks, etc. - is correct and functioning right. Also, make sure your idle RPMs aren't set too high.

Thanks, that sounds like the way to go and what I've been moving towards the more I learn. And, that should include carb clean and rebuild with kit right? Or should I try the other stuff first? I'm a little nervous of making things worse talking it all apart and back together, but learning and tinkering is part of the fun for me. Here in NYC I don't have a full garage, just a parking space in a condo garage and a job box I can store tools. I have to tidy up when I'm done for the day. My idle is too low if anything, I have to stay on the gas to ensure it doesn't die. Though, once it runs for a while, then I've seen it hang out at over 1000 rpm which is too high.

 

[3pedals]

Hey NYC! Another big welcome from Texas. That’s a beautiful car…. yellow & black is a show stopper. The car sure looks well cared for. What’s the back story on the car, where it came from and how you found it?!?

You are definitely in the right place for help, these members are on top of their game.

Good Luck!

I bought from a father/son classic car dealer in Miami (who had multiple storage units with amazing stuff. Pic below) and they got from PO in Iowa. I think that guy just needed to sell for some cash. I found ad on Ebay and flew down to see and test drive it, then had it shipped up here. Based on the receipts it came with, looks like the restoration work happened primarily back mostly in 2006. It's got the Demon carb, A/C unit, unilite distributor, ram air added. Could be just missing more but last receipt date is 2010.

 

[Sheriff41]

Thanks, that sounds like the way to go and what I've been moving towards the more I learn. And, that should include carb clean and rebuild with kit right? Or should I try the other stuff first? I'm a little nervous of making things worse talking it all apart and back together, but learning and tinkering is part of the fun for me. Here in NYC I don't have a full garage, just a parking space in a condo garage and a job box I can store tools. I have to tidy up when I'm done for the day. My idle is too low of anything, I have to stay on the gas to ensure it doesn't die. Though, once it runs for a while, then I've seen it hang out at over 1000 rpm which is too high.

I would try the tune up before opening the carburetor. If the tune up doesn't clear up the issue then dig into the carb. The Unilite takes the points/condenser out of the equation. Someone more experienced with the Unilite may have some advice setting up the timing curve. Take photos of the plugs if you want someone on here to read them for you and let us know if you find anything you think is not right.

A rich condition, incorrect timing, wrong temperature range plugs, carbon buildup among others are all things to could contribute to your backfire and run on conditions.

 

[1973 Mach-1]

I agree with Sheriff41. Before digging into anything like the carb, I'd take a look at something more simple. With the symptoms you are sighting, it sounds like it could be something as simple as too advanced or ******** timing. You might want to do yourself a favor and check that first.

 

[Kilgon]

Welcome from south west Ohio. Nice looking car and thanks for the info about it. As many have already mentioned, I would start by first looking at the plugs. Run on and back firing from the carb would indicate either foul plugs, wrong plug heat range or running to lean. Any of these conditions can cause the plug to be hot enough to the point where it will ignite fuel as it enters the cylinder. Odds are that is where your problem is. Let us know what you find and if you have any there is plenty of help here for you.

 

[James Bond]

Welcome from Oregon, nice looking car.

 

[cjstaci]

Welcome from Seattle, and New Mexico later this year. Congratulations on your nice looking car.

 

[Bill Perkins]

Bought a 73 Q code, 4 speed manual a month ago. Been wanting a 71-73 for over 20 years. This one is very clean overall, but not idling great. Coughs through the carb sometimes, has done a few loud backfires while driving, sometimes will die at idle on its own, has done a little bit of dieseling after shutdown after running for a while.
I haven't had a carb car for a long time so working through issues is new to me. I've got a carb rebuild kit (road demon) and planning to clean it, check condition of all the spark plugs, measure vacuum, etc, and see if I can get it running nice myself. Wish me luck!

View attachment 77168

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Nice Car

 

[Bill Perkins]

Welcome from Opelika, Alabama

 

[Steve McMahan]

Welcome from So Cal. That’s a beauty. You’ve already received all the advise you need.

 

[rio1856]

Welcome from SW Florida! Awesome looking sled there my friend.

 

[tfowler9]

Welcome from the Heber Valley, Utah!

 

[Bobby]

Yet another Howdee from Texas! Slick ride! Here's my take. Replace the plugs, wires, cap and rotor. Upgrade to a Pertronix Ignitor and be rid of the points and condenser. An oil and filter change is also a good idea since you don't know how long your ride has been in storage. Make sure your PCV system is in good order and there are no vacuum leaks. Run carb cleaner in and around the carb and make sure you've got good gas in the tank. If unsure, siphon the gas out and go get 5 or so gallons of 93 octane ethanol free gas. I call it sugar free gas. You then have a good baseline for your engine and maintenance is sure. Having a nice stick instead of an auto tranny solves a lot of potential problems. If you still have issues, rebuild the carb!

 

[3pedals]

Yet another Howdee from Texas! Slick ride! Here's my take. Replace the plugs, wires, cap and rotor. Upgrade to a Pertronix Ignitor and be rid of the points and condenser. An oil and filter change is also a good idea since you don't know how long your ride has been in storage. Make sure your PCV system is in good order and there are no vacuum leaks. Run carb cleaner in and around the carb and make sure you've got good gas in the tank. If unsure, siphon the gas out and go get 5 or so gallons of 93 octane ethanol free gas. I call it sugar free gas. You then have a good baseline for your engine and maintenance is sure. Having a nice stick instead of an auto tranny solves a lot of potential problems. If you still have issues, rebuild the carb!

Thanks, good idea on fresh gas, it's pretty low now and was planning to do full tank of 93 and got a bottle of techron fuel cleaner to "clean" the carb (not sure how much that will accomplish).

So, per the other suggestions here, I pulled a couple plugs, the #1 and #2. Was struggling to get more as I need a flex ratchet I guess to get at the plugs easier. They're Autolite 25, which seems like the correct temp rating.





I know I should pull all of them, but these two look pretty similar. What's the diagnosis here?

I got a timing light and checked idle and it looked pretty low, like 4 degrees. So, from what I've read, it should be more like 12-16 degrees of initial timing at idle. So, that's one thing to try?
Also, I looked up the Demon carb port diagram and it looks like it's hooked up to manifold vacuum (second port from the corner), not ported. From what I've read, having higher initial advance and hooking up to ported is the better option for street drivability.




So, I'm thinking I should swap to the ported outlet and advance the initial timing to 14 degrees or so. I've got a vacuum gauge coming so I will try to set to maximize the vacuum reading.

Also, just replace all the plugs. And get the new gas in there.