1977 Pontiac Firebird Back fire not running

Tiny
TOPCOP5129
  • MEMBER
  • 1977 PONTIAC FIREBIRD
  • 6.6L
  • V8
  • RWD
  • AUTOMATIC
  • 80,000 MILES
Hi, the car is actually a 1949 Chevy deluxe with a 1977 pontiac firebird/trans am 400 CID in it. Here's the problem I'm having. The engine has a healthy hiccup and backfire. It's even caught fire a couple of times! To explain in detail.

I purchased the car thinking that the car needed a tune up or the carburetor was shot. When the seller showed me the car he had to pump the hell out of the gas to get it to start. Then for the first few miles had to two foot it to keep it running! Now I just assumed old carb along with no choke, car is cold therefore that explains the two feet driving! Well little did I know even when the car is hot the first few miles you have to two foot it. While sitting at idle at a stop light in gear the engine would also randomly make a hiccup feeling, kinda like when you have a bad motor mount that slam you would feel throughout the car. It would make that feeling every time sitting in drive, Never at the same time as if the cam was worn but just very spur attic. Also the car had A heavy vibration.

What I've done explained in detail
I went with my gut, purchased a new edelbrock 650cfm, changed the plugs wires, pulled carb off seen that it was a single plane manifold so I changed that to a dual plane manifold. I installed the new carb, set the timing (distributor is an hei) which was advanced to 30+ before tdc. Along with the plugs being gapped out close to 100. And at this point the car became even harder to start, ran a lot worse and the car was set to factory specs. The internals are stock for this engine. I finally felt that I got it running decent enough to take it for a ride
As luck would have it I backed it out of my driveway and the car just died? No backfire, no sputter nothing. It
Was like I turn the key off. Well the car was on fire! Carb was burning and ended up burning my hood.

I returned the new edelbrock with hopes that it was the problem and went with a Holley 600 cfm. I installed that, had to reset timing again? Got her to fire up rather easily. I thought this solved the problem but it didn't ! I took the car around the block, same problems as before just a lot worse along with backfiring. Got her home, was messing around with it and realized that if I hold the throttle underneath the hood at a steady 1200 rpm the engine began to bog down really bad and moments later backfired slightly and I had another fire to put out! In order for me to get the car started again I had to move the timing around to get it to fire after, it was already set! I also noticed will setting the timing there doesn't seem to be much of a diffence in running style when I remove the vacuum advance line. Btw I did properly adjust the carb.

My thoughts
I've been building and working on these old junks forever and have NEVER been stuck like this before! I can't stop going back to the thought that the timing chain is shot! Like is jumping a tooth or something along the lines of that. I just don't have the funds with a house full of kids lol, so I really just wanna fix what needs to be fixed.

Thank you so much! This is driving me nuts and I really wanna get it figured out. I really hope I supplied you with enough information

Dave Ruckoldt
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Saturday, October 18th, 2014 AT 7:08 AM

2 Replies

Tiny
CJ MEDEVAC II
  • MEMBER
I'M A JEEP KINDA GUY, NUTHIN' BUT, SINCE I WAS ALLOWED ON THE ASPHALT IN '81!

MY JEEPS AND MOST OF THE OTHER JEEPS I HELP OTHERS WITH ARE MOSTLY STOCK OR VERY MILD MODIFICATIONS

MY CURRENT '77 HAS A 258 STRAIGHT 6 WITH A 4 BBL OFFENHAUSER INTAKE AND A HOLLEY 390 CFM CARB. RECENTLY I INSTALLED A TRUE DOUBLE ROLLER TIMING CHAIN BUT OUT OF THE 3 CHOICES OF TIMING MARKS TO USE, I USED THE "STOCK MARKS", AS I HAD NO NEED TO MODIFY MY VALVE TIMING

(I HAVE NO IDEA WHAT KINDA CHAIN YOU HAVE, OR WHETHER THE LAST FELLER COULDA USED THE OTHER 2 CHOICES OF THE MARKS TO ADVANCE OR RETARD THE VALVE TRAIN - BUT IT MIGHT BE SOMETHING TO CONSIDER, IF YOU RUN OUT OF "EXTERNAL POSSIBILITIES")

WHAT KINDA FUEL PUMP YOU GOT GOIN'?

I RECKON YOU MIGHT BE AS UP ON TWEAKIN' AS I AM, LISTENING TO YOUR STORY

I'LL THROW SOME JUNK IN THAT OTHER FELLERS "HIT" ME WITH IN THEIR QUEST TO MAKE A JEEP RUN RIGHT

1) ARE YOU TIMING AT CURB IDLE SPEED?

2) ARE YOU TIMING WITH THE VACUUM ADVANCE VACUUM HOSE LOOSE AND PLUGGED OFF - THERE AGAIN AT CURB IDLE SPEED?

3) ARE YOU USING A PLAIN JANE TIMING LIGHT OR ONE WITH A DIAL (THAT YOU REALLY HAVE NO IDEA WHAT IT'S THERE FOR, AND MAKE UP YOUR OWN WAY TO USE IT!)

4) MY '77 CJ-5 IS TIMED PERFECTLY AT 8 DEGREES BTDC, HOWEVER IT DOES RUN MUCH MORE PERFECTLY IF I USE "MANIFOLD VACUUM" INSTEAD OF "PORTED VACUUM" ON MY VACUUM ADVANCE ON MR. DISTRIBUTOR, I DO HAVE TO RUN MY IDLE BACK DOWN TO CURB IDLE ONCE I ATTACH IT.

5) HAVE YOU LOOKED INSIDE THE OLE 'STIBUTOR TO INSURE THE MECHANICAL ADVANCE WEIGHTS ARE NOT FROZE UP, OR THE SPRING(S) ARE NOT BROKEN (WHICH WOULD RENDER IT "ALWAYS ADVANCED" UNABLE TO RETRACT) (ALSO WOULD ALWAYS REMAIN TIMED AS YOU TIMED IT, EVEN WHEN ENGINE SPEED INCREASES)

6) REPETITIVE LOOKING AT STUFF MIGHT FOOL YOU, ARE YOUR WIRES ON THE DISTRIBUTOR RIGHT? (SEEN A FELLER BRAGGING ABOUT HIS "LOPE" ONCE, TURNS OUT, HE HAD 2 WIRES SWAPPED)

YOUR TURN

THE MEDIC
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Saturday, October 18th, 2014 AT 7:59 AM
Tiny
JACOBANDNICKOLAS
  • EXPERT
At 30 BTC, I'm surprised it started at all. The backfiring through the intake has me concerned. First, have you checked for engine vacuum leaks? As far as the timing, have you confirmed that the timing chain hasn't jumped? Finally, have you checked compression to make sure you don't have some burnt valves?
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Saturday, October 18th, 2014 AT 5:32 PM

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