Backfiring after WOT and backfires on decel, even at low speeds.

[MrSony]

Although this is about my '70 T-Bird, I'm sure the principles are the same for all 4 barrel carbs. After a more that part throttle (passing on highway, on ramps, etc) the car backfires with a loud pop and continues to burble like popcorn in a microwave until a full stop then it idles like butter. Also if it's cold, like just started for the day, or after work or school, it bogs like hell I can hardly give it any gas and it dies. Don't know the model # off the top of my head, but it is a newish 600cfm holley on a ford 429. It has an electric choke if that helps. The car runs great and strong, but it's slowly getting irritating. I've tried adjusting the carb, that helps a bit, but it soon does it again. Any help is appreciated. Also it has MSD electronic ignition, blaster coil, 6A box, and new wires and plugs and new dual exhaust with H pipe going into flowmaster (I think) 40s series mufflers.

 

[drogg1]

Hmm it sounds like an ignition problem but if everything is new then probably not. Maybe double check the plugs and wires to be safe as well as make sure the initial timing is right and that the advance works properly.

The popping and burbling on part throttle acceleration would point to carburetor problems otherwise. A pop or backfire like that usually is caused by a lean condition. When you suddenly accelerate, the carb must provide more fuel quickly to compensate for the greater air intake. To enhance throttle response, most carbs have an accelerator pump to add an extra shot of fuel between transitions. If the pump on your carb was worn, you would notice bogging with quick changes in throttle.

The stalling when cold could also be a lean condition. This is easy to check for. Hand-choke the carburetor by putting your hand over the carb. If the engine speeds up, this means the idle mixture is lean or there is a vacuum leak. A vacuum leak might explain both the issues.

 

[lilbowtie]

I take it it's on deceleration only - your getting fuel with the throttle closed. Could be a variety of things fuel pressure, float adj but I'm guessing the setting are off. The biggest is everyone wants to play with the blade setting and once they are set - shouldn't be touched. Read up and set your whole carb up.

 

[pontiacgp]

sound like there is a leak in your exhaust and it's drawing in air on deceleration or it's running lean

 

[MrSony]

There might very well be an exhaust leak. And I guess I should have been a bit more clear, it bogs when COLD and sometimes dies giving it anymore than half throttle, but once warmed up it's perfectly fine. And it pops and gurgles on DECEL only, WOT is fine along with just part throttle like passing someone. As soon as I let off, it starts softly burbbling.

 

[CWPottenger]

To a certain degree that is normal with a cold engine. Check your choke for proper operation and adjustment. You can set it richer or leaner as needed. Pop on decel is also normal to a certain degree as long as it is minor lean pop. If you adjust your secondary plates slightly open at idle this will help reduce the "pop"

 

[pontiacgp]

from what I have read if that carb isn't a motorcraft holley you need a 650 to 750 holley or edelbrock for the 429. Ford tweaked their holley carbs to run the 429

 

[MrSony]

Well, back in '70 the stock CFM carb for the t-bird was a 605 CFM Autolite. Wouldn't a 600cfm for daily driving be sufficient? Or would it really benefit that much from a 600 to 650/700/750 swap?

 

[joesregalproject]

600 cfm is pretty small for that big 429. If it was meant to run on a 605 cfm and you are going to use a 600, you would probably need to set the adjustment screws to the rich "extreme" side. You'd be best off with a 650 IMO if funds allow but you can probably get by on that 600 with it tuned well. Still definitely sounds like a lean condition to me though, at the very least I'd rebuild the carb and have it retuned.

 

[MrSony]

UPDATE: now for the most part wont run/idle at ALL when its below about 32degrees unless its at op. temp. And at operating temp, which on my T-Bird is about "M" on the temp gauge, a little more than half way since I replaced the little sender in the intake, it runs and idles more or less fine unless I goose the throttle too abruptly. It's like it startles it or something lol. Getting annoying.