Carb backfire in a 1968 Mustang

RTALON235

MEMBER
1968 FORD MUSTANG
V8
2WD
AUTOMATIC
100,000 MILES

The situation:

1968 Mustang with a 2bb 289. Had an ignition problem and ended up sitting for a year thanks to time and money issues. It ran perfectly, just wouldn't start at the ignition switch. Once the time and money issues were resolved, I got under the dash and replaced the switch. Problem is, now she won't start at all! The engine turns over fine and she tries to start, she just can't keep going and is backfiring through the carb.

Corrective things done so far:

1. Rebuilt carburetor due to minor fuel leak
2. Replaced coil, battery, and ignition switch.
3. Traced/repaired all ignition wiring
4. Verified correct circuit pathways via Chiltons manual
5. Replaced fuel filter, drained old fuel and replaced with fresh fuel
6. Verified correct firing sequence, replaced plugs, wires, rotor and distributor cap.
7. Checked all vacuum hoses

According to Chiltons, the issue is ignition timing, a bad EGR component, or a defective TAC vacuum motor or valve.

The car is a 68 and doesn't have an EGR, or a TAC vacuum motor. The thing I can't figure out is how ( if at all ) the timing got out of whack since nothing has been done to change the timing, So, I'm at a complete loss as to what is wrong.

3 Replies

CJ MEDEVAC

MECHANIC
11,005 POSTS

GIVE IT ABOUT 3 SODA BOTTLE CAP-FULS (TOPS/ LIDS)OF FUEL DOWN THE CARB

TRY IT

RESULTS?

THE MEDIC

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Saturday, August 20th, 2011 AT 2:10 PM

CJ MEDEVAC

MECHANIC
11,005 POSTS

WHILE YOU'RE AT IT

KEY OFF, ROLL YOU ENGINE AROUND BY HAND, PUT YOUR TIMING MARKS ON ZERO

(THIS IS JUST FOR A "QUICK OBSERVATION", TO SEE WHAT'S GOING ON, TOO DO THIS PERFECT, WE'LL HAVE TO FIND COMPRESSION STROKE, LET'S SORTA WAIT, TO DO THAT!)

SINCE YOUR CRANK TURNS TWICE, TO TURN THE CAM ONCE.

IF YOU REMOVE THE DISTRIBUTOR CAP, YOUR ROTOR SHOULD BE POINTING AT #1 PLUG WIRE. IF IT IS NOT. ROTATE THE ENGINE EXACTLY ONE REVOLUTION. LINE UP THE TIMING MARKS ON ZERO AGAIN. NOW IT SHOULD BE POINTING AT #1 PLUG WIRE

OUR OBSERVATION SHOULD BE, ON ONE OR THE OTHER, REVOLUTION, AND MARKS CORRECT. IT DOES POINT AT #1 WIRE

THE ONLY THING THAT MAY DISPROVE THIS IS, IF THE DISTRIBUTOR "WAS" REMOVED, IT COULD HAVE BEEN REPLACED 180 DEGREES OUT. IT WAS NOT PUT IN RIGHT, IF IT WAS REMOVED (WILL NOT BE POINTING AT #1). JUMPED TIMING? IS A POSSIBILITY.

DEPENDING ON THESE RESULTS, I CAN EXPLAIN PROPER INSTALLATION. NO BIGGIE!

THE OTHER "STUPID" POSSIBILITY IS YOUR PLUG WIRES ARE NOT CORRECTLY INSTALLED. MAYBE YOU HAVE 'EM RIGHT, SEQUENCE WISE. JUST GOT ROTOR BUTTON ROTATION CONFUSED, AND YOU INSTALLED IN THE WRONG DIRECTION

IF YOUR ENGINE IS STILL ON THE TIMING MARKS. ROTOR IS POINTING AT #1 WIRE---THAT'S YOUR SEQUENCE STARTING POINT

REGARDLESS--IF IT'S NOT THAT SIMPLE. LET ME KNOW, AND I CAN EXPLAIN THE EZ WAY HOW TO FIND COMPRESSION STROKE AND VERIFY THE DISTRIBUTOR IS INSTALLED RIGHT. OR I WILL EXPLAIN HOW TO GET IT RIGHT!

THE MEDIC