Hey all, as stated in the title, I am having drivability issues with my pickup. 1977 F-150 with a 429 out of a ‘73 Galaxie. I recently resolved a vacuum issue which significantly improved my idle, but did not fix the backfire/bogging under acceleration. I installed a new Edelbrock performer carb and tinkered with the idle mixture screws with a vacuum gauge. Is it possible I am way off in terms of carb tuning? I should add that the engine sounds great and revs without hesitation when in neutral with no load on the drivetrain. Any help would be appreciated!

 

was this an existing problem or did it start with the new carb ?

 

440 Sixpack I’m not sure…the old carb had a broken accelerator pump and the rear end was shot so I didn’t get to drive it prior to the new carb. I’m wondering if my distributor/coil isn’t functioning properly?

 

Could be... Or not...
In other words, a lack of proper ignition advance can definitely bog down your acceleration quotient. But so can a carburetor that goes lean when accelerating under load.

Your idle screws do next to nothing for acceleration, or for that matter, just about anything else other than idle. The rest is all handled by other circuits, primarily the main jets (and in your case metering rod) combinations as well as accelerator pump settings.
Have you given the engine a once-over in the tune-up department? What is your ignition timing? What does the advance curve look like when you rev it up while watching the timing marks?
Are you still running an electronic ignition, or does your swapped-in engine have a points distributor? If electronic, what model?

Next time you're out at the truck, before you start the engine pop the air cleaner off and look down the carburetor while pushing the throttle lever back and see if there is a good healthy squirt of gas each time you push the lever.
Oh, and make sure the choke is fully opening when warm. I would think that a partially closed choke could give you some fits under load. Not from a lean mixture in that case, but from not enough air being able to get in when needed.

Good luck. Just a few things to look at. I'm sure others will have more things to add.

paul

 

Lots of things it could be but I'd start with checking the timing then move on to carburation.

Your timing will need to be tweaked for best performance but if you haven't already done it set it to specs first. then hopefully you have a dial back to check your mechanical advance but if not use your light and at least make sure it's advancing at all.

If that's ok you might be running lean. I hate AFB's so my solution would be the garbage can and find a Holley but maybe someone here can tell you how to check the float level . an easy way to rule out fuel delivery problems is if you have another carb just throw it on and if it solves the problem you know what to do. it's a real time saver.

There's more if it's not any of this but that's how I'd go at it.

 

Thank you guys. Lots of great advice and now I have I checklist for the weekend. Not sure what I would do without the internet!

 

FYI the idle circuit is still effective through light throttle/cruise. The blades just aren't open enough to start the booster circuit, Might not have any bearing here.