Spark plugs
#1
Huh  I am trying to figure out what plug should be in my Mach 1, its a 71, 351C, "M" code. Just been rebuilt, had to bore it .30 over, basically kept everything as close as possible to stock.  Just put a Holley 735 Quick Fuel carb on it.  It does also have headers.  Right now I have Autolite 24's in it.  That was what was in the car when I bought it 5 years ago. Just put a new set of plugs in it, but the ones that came out were all black except for #4, it was brown.  The Chiltons Manual says it should have ARF 32's and I have no clue what brand that would be, so I need some thoughts on what plug to use....Thanks!!
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#2
As far as plugs go the ARF 32 sounds right. I believe that is the old Big, 13/16 plugs. The brand would be an Autolite, Motorcraft, or FoMoCo. Which are all Ford. and I sure wouldn't run any thing else in it. As for all the plugs being black. That says the fuel mixture is rich, meaning to much fuel. Things to check. 

1 Choke sticking? with the warmer weather shouldn't be an issue unless grossly misadjusted, or???

2 Float setting? I'm assuming Carb is new, so shouldn't be an issue. But you never know. It is a Holley.

3 Fuel pressure? Stock mechanical pump, shouldn't be an issue, electric pump? check pressure!

4 Jet sizes? After making sure all of the above is correct. Go down about 2 jet sizes, at a time until they are all light tan or brown. 

Hope it helps. Let us know how it goes. 

JTS
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#3
(05-17-2020, 05:38 AM)JTS71 Mach1 Wrote: As far as plugs go the ARF 32 sounds right. I believe that is the old Big, 13/16 plugs. The brand would be an Autolite, Motorcraft, or FoMoCo. Which are all Ford. and I sure wouldn't run any thing else in it. As for all the plugs being black. That says the fuel mixture is rich, meaning to much fuel. Things to check. 

1 Choke sticking? with the warmer weather shouldn't be an issue unless grossly misadjusted, or???

2 Float setting? I'm assuming Carb is new, so shouldn't be an issue. But you never know. It is a Holley.

3 Fuel pressure? Stock mechanical pump, shouldn't be an issue, electric pump? check pressure!

4 Jet sizes? After making sure all of the above is correct. Go down about 2 jet sizes, at a time until they are all light tan or brown. 

Hope it helps. Let us know how it goes. 

JTS
Thanks for the info! I have been online looking for those plugs and the only one I can find is the Auto lite.  Been researching this all weekend and talking to whomever might have any thoughts and the one plug that came up more than any is the NGK UR5.  Still looking for the Motorcraft plug though.  Will also be checking your suggestions you listed for the black plugs.  Thanks a lot!!!
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#4
Life with an older Muscle Car, can be a lot tougher then today's cars with all the fuel injection, and computer controls. They have taken away all the "old school" maintenance, and skills. Things us older guys, did on a weekly basis sometimes. It's amazing we were able to drive them everyday without a thought.  Cool

   You're welcome and please don't hesitate to ask, if you can't figure something out. Cause there is enough good people here, somebody knows the answer. Good Luck. Wink

JTS
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#5
(05-18-2020, 08:12 AM)JTS71 Mach1 Wrote: Life with an older Muscle Car, can be a lot tougher then today's cars with all the fuel injection, and computer controls. They have taken away all the "old school" maintenance, and skills. Things us older guys, did on a weekly basis sometimes. It's amazing we were able to drive them everyday without a thought.  Cool

   You're welcome and please don't hesitate to ask, if you can't figure something out. Cause there is enough good people here, somebody knows the answer. Good Luck. Wink

JTS
Okay, so for starters, the plugs you listed, on the Motorcraft, can you help me with what  or what one to get and the heat range?  I am still trying to find the older big ones..... and as far as that goes, any #'s of plugs that are the equivalent heat range of a NGK UR 4.  Thanks again!!
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#6
You are a "Problem Child" LOL! just kidding it can be very frustrating trying to look up info. 

Ok, lets see if this helps. 

The NGK you listed is UR4 this is the same as a

 Motorcraft 25

Or, an Autolite BRF42 which is what my "Haynes" manual for the Mustang, says is stock. 

The Champion number is RBL-15Y

AC (GM) is a 44 TS

They are all stock choices for you M code Mach 1. 

I also listed a link to the Autolite/Motorcraft spark plug site that will show you tons of info on spark plugs as well as the cross over charts I used to find all the correct plugs. I know these numbers are correct, as I've seen all of them used over the years. They are all the same heat range. To go to a hotter plug, go down in the number. For example, a 24 is hotter then a 25. 

a    UR3 would be hotter then a UR4. And so on. 

One other thing is the R listed on "any" plug, simply means the plug itself, has a resistor in it. 

Hope it Helps. 

JTS

https://www.autolite.com/resources/tech-specs
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#7
JTS71 Mach1You are a "Problem Child" LOL! just kidding it can be very frustrating trying to look up info. 

Ok, lets see if this helps. 

The NGK you listed is UR4 this is the same as a

 Motorcraft 25

Or, an Autolite BRF42 which is what my "Haynes" manual for the Mustang, says is stock. 

The Champion number is RBL-15Y

AC (GM) is a 44 TS

They are all stock choices for you M code Mach 1. 

I also listed a link to the Autolite/Motorcraft spark plug site that will show you tons of info on spark plugs as well as the cross over charts I used to find all the correct plugs. I know these numbers are correct, as I've seen all of them used over the years. They are all the same heat range. To go to a hotter plug, go down in the number. For example, a 24 is hotter then a 25. 

a    UR3 would be hotter then a UR4. And so on. 

One other thing is the R listed on "any" plug, simply means the plug itself, has a resistor in it. 

Hope it Helps. 

JTS
I am not trying to be...lol  After all the work for the last 5 years, I want it right and I am soooooo close...lol  Will check out those plugs, but wanted to say, from what I have been told, the NGK numbers go down for a hotter plugs, but all the other brands you named, supposedly for a hotter plug, they go up.  Will have to get that figured out.  I do think you for all the help though.  Since I have been in the Mach 1 club, I have gotten more help here than any other!!!  Thanks again and hope to get a video and more pics on here.  Laterzzzzz
https://www.autolite.com/resources/tech-specs
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#8
Not a Problem. I was Joking when I said you were a Problem Child.
 Glad to be of help. I'd go for the Autolite, or the Motorcraft plugs if I was doing it. 

JTS
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#9
(05-23-2020, 09:54 AM)JTS71 Mach1 Wrote: Not a Problem. I was Joking when I said you were a Problem Child.
 Glad to be of help. I'd go for the Autolite, or the Motorcraft plugs if I was doing it. 

JTS
I am going to try to go for the Motorcraft 25 and hope they have a 25R someplace.  With electronic ignition, feel that is a good idea.  Thanks again for all the help.  Will let you know how things turn out ; )


ProblemChild
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#10
Good Deal  Cool

JTS
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