Excessive backfire thru carburator - 69 road runner 440 w/4 bbl

[paladin06]

Well I started the car for a Sunday show and it was excessive back firing thru the carb. I mean really bad. Looked at the plug wire positions on the distributor cap, they did not match the shop manual. The plug wires are in the position they were when I got the car two months ago. I moved all wires to match the shop manual, now the damn car will not start. PLEASE HELP!!

 

[Pops1967GTX]

Did your timing chain jump? is a possibility Thinking spark plug wiring is not correct.....B/RB/Hemi engines have a CCW distributor rotation....Firing order on 440 engines is 1 - 8 - 4 - 3 - 6 - 5 - 7 - 2...Pull dizzy... Crank Motor over #1 is on compression cycle..Rotor should be inline with the #1 spark plug wire..

Firing Order
For all engines 1-8-4-3-6-5-7-2
Left side cylinders are numbered (from front) 1-3-5-7
Right side cylinders are numbered (from front) 2-4-6-8

 

[paladin06]

Thanks Pops. Will do tomorrow.

Did your timing chain jump? is a possibility Thinking spark plug wiring is not correct.....B/RB/Hemi engines have a CCW distributor rotation....Firing order on 440 engines is 1 - 8 - 4 - 3 - 6 - 5 - 7 - 2...Pull dizzy... Crank Motor over #1 is on compression cycle..Rotor should be inline with the #1 spark plug wire..

Firing Order
For all engines 1-8-4-3-6-5-7-2
Left side cylinders are numbered (from front) 1-3-5-7
Right side cylinders are numbered (from front) 2-4-6-8

View attachment 153304

 

[Rich Kinsley]

It sounds like it's way too retarded. Don't forget the famous KISS. It's not likely anything suddenly changed in your valve train if it was OK before. The dist may have been installed incorrectly. It's OK to move the wires around the cap as long as the order is correct. That may have been what was done in order to get enough advance before and you just put it back with less advance. Loosen the dist and increase the advance when you try to start it. The idea about finding TDC is your best trouble shooting bet. But to get it going just try putting the wires where they were and advancing it.

 

[Plucked Chicken]

Easiest way to find TDC is pull the driver's side valve cover and turn it over until both valves are closed, and piston is at the top of it's travel. Then the rotor should be pointing at number one on the cap.

I had a 472 Cadillac engine jump time after 15 minutes of running due to a stripped distributor gear, from lack of oiling. When I got it at TDC as described, the rotor was pointing a couple terminals off from TDC. Assumed it was timing chain until I saw the tomb.......

ccasion17:

 

[dryheat]

I'm in Glendale if you need some on-site help or a second pair of hands/eyes.

 

[paladin06]

So it's safe for me to assume all is steel with the gear, chain and distributor?

 

[dryheat]

Back in the day Plymouth used nylon camshaft timing gears. I had to rebuild a 69 Road Runner 383 in the mid-seventies because of that ... so if the motor has never been touched it may be worth looking at.

 

[paladin06]

Thanks to you good folks and these guys. I did the finger set for # 1 TDC. Hit 10 degrees, set the number 1 by the rotor location. Relocated all the wires. She fired right up and no BF through the carb. Will complete the rest tomorrow.

Thanks guys!!

 

[paladin06]

Did a short test drive last night. Felt a little sluggish and slow restart. Bumped the timing to 14 degrees BTC. One more time around the block. Bumped her to 17 degrees. Last lap and she is strong. Restart just by leaning in the car and turning the key. Gave her some gas to about 4500 rpm, no back fire and she sounds awesome. Thanks all. Now where did I put that kick panel insulation? :icon_scratch:

 

[ODZKing]

I was going to ask about the wiring as well. I had 2 wires flip flopped on my 73 and it was backfiring badly thru carb.
I had 4 and 6 reversed. Once I corrected that, problem gone!

 

[ArtH]

Did a short test drive last night. Felt a little sluggish and slow restart. Bumped the timing to 14 degrees BTC. One more time around the block. Bumped her to 17 degrees. Last lap and she is strong. Restart just by leaning in the car and turning the key. Gave her some gas to about 4500 rpm, no back fire and she sounds awesome. Thanks all. Now where did I put that kick panel insulation? :icon_scratch:

Any time I've had an engine backfire through the carburetor, more times than not it was due to retarded ignition timing. I learned that years ago when I took some courses at the local technical college which included engine rebuilding. The first time I fired up my project engine, that's exactly what it did...back fired through the carb. The instructor told me to advance the timing and that solved the problem. After that I was able to dial in the correct timing and the engine ran great for a number years until I sold the car. Since then, the first thing I try when I have back fire through the carb is to advance the timing. Secondly, I check for vacuum leaks. Once had an engine back fire through the carb and start on fire. It was due mostly to not plugging the large rear port on the carb which is used for the power brake system. One of our instructors told us that you if could start a warm engine with a short turn of the key, as you mentioned you did, it was a good sign it was in tune.

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I was going to ask about the wiring as well. I had 2 wires flip flopped on my 73 and it was backfiring badly thru carb.
I had 4 and 6 reversed. Once I corrected that, problem gone!

I did the same thing once when I got in a hurry changing plugs and wires. The engine actually idled pretty decent, not great but okay. But, when I test drove it was awful. Retraced my steps and sure enough No 4 & 6 were crossed up. Fixed that and all was well. Point is, sometimes dumb little mistakes create problems that we tend to over diagnose. Try the easy stuff first.