Engine running rough and backfiring

7173Mustangs.com

Help Support 7173Mustangs.com:

elliotmoore930

New member
Joined
Mar 2, 2019
Messages
4
Reaction score
0
Location
Dallas
My Car
1972 Mustang Grande; 302 engine
Hello. I have been having trouble with my 72 Mustang 302 with the engine running really rough and backfiring. I was driving along the road fine when it just started running real rough like some of the pistons were not firing. Initially, I thought it was a fuel delivery problem, so I replaced the filter and checked the lines for blockages. This did not solve the problem. 
Next, I thought that it was an ignition problem. First, I replace the spark plugs because a few were cracked which didn’t help. Then I tried the distributor.  I have an HEI, and I bought a tune up kit complete with new coil, cap, rotor, control module, mechanical advance, and wiring harness as well as new spark plug wires. Installed all of these parts on, and the car still runs horrible. I am out of ideas as to what the problem might be, and I am open to ideas. 

 
Joined
Jan 1, 2012
Messages
8,233
Reaction score
969
Location
Springfield, OR
My Car
1971 Mustang Sportroof M code
How often were you driving the car before the problem started? Had the car been setting for any length of time between drives?

In hot weather it doesn't take long for the fuel to evaporate out of the carburetor, leaving varnish behind.

 

elliotmoore930

New member
Joined
Mar 2, 2019
Messages
4
Reaction score
0
Location
Dallas
My Car
1972 Mustang Grande; 302 engine
No, I drive it daily. It was running fine for about 5 min before it started running rough. 

 
Joined
Jan 1, 2012
Messages
8,233
Reaction score
969
Location
Springfield, OR
My Car
1971 Mustang Sportroof M code
I suspect your carburetor has some plugged passages. One thing that will crack spark plugs is a lean mixture, causing excess heat in the cylinder, and probably some pre-detonation and backfiring. It has likely been getting worse over time and finally reached the point where the mixture is too lean for the engine to run.

 

bossmanbob

Member
Joined
Jul 26, 2012
Messages
14
Reaction score
0
Location
N Calif.
My Car
1971 Boss 351.CHI heads,Baer brakes,Total Control suspension.
If it started w/ a backfire, I would suspect a partially sheared distributor drive gear pin.

 
Top