Engine bogging down, 1969 300, standard 440

[ArnieJr]

Hello, I'll be the first to admit I only know slightly more than the average bear when it comes to engines and near null on carburetors.

Quick backstory: I had a minor engine fire last year that melted some ignition wires and damaged the coil and carb beyond repair. I has the wires and coil replaced and the carb upgraded to an Edelbrock 750 (I think the old one was 600 or 650 before and 750 was all my mechanic could find).

The idle is rough (but about right, 670 - 680 RPM) but smooths out once I get up to cruising speed, but acceleration seems a bit sluggish and when it gets up to about 90 or 95, the engine seems to bog down (I used to be able to get it up to around 100 with just a little coaxing).

I'd had a tune up prior to the fire, so I think I can safely eliminate timing, ignition or spark plug issues.

My mechanic did say he saw a fuel pressure regulator in line after the fuel pump and said he'd never seen that before. I don't remember if I had him remove it or not. Were those stock and could that be the reason? It does seem like it may not be getting enough fuel.

I know the easy answer is take it to the shop, but I do want to learn how to do some of these things. It's one of the reasons I bought the car.

 

[rags]

I'd had a tune up prior to the fire,

maybe the fire roasted the vacuum advance. fuel pressure regulators are not stock.

I do want to learn how to do some of these things.

buy yourself a vacuum gauge, a basic timing light, and a basic test light with an incandescent bulb. become adept with using those three tools and you can diagnose just about anything.

 

[ArnieJr]

check on those first two, reading up on that. thx

 

[rags]

I think I can safely eliminate timing, ignition or spark plug issues.

when doing diagnostics never discount a possibility. always verify as much as possible. it's the simplest things that cause the biggest problems. i've seen so many instances of where problems could have been resolved with a good physical inspection.

 

[volksworld]

provided ignition timing and advance checks out, be advised that aftermarket performance carbs are usually not a ''plug and play'' situation ...and Edelbrocks are a bit more complicated than Holleys when it comes to jetting ...instead of just using jets with varying size holes to optimize fuel delivery Edelbrocks also have tapered metering rods that locate inside the jets...these are spring loaded and vacuum operated to allow more or less fuel to flow through a given size jet under different operating conditions...Edelbrock sells a calibration kit with the stuff to do this...so the end result is they are more precisely tunable but doing so might be beyond the capabilities of even your mechanic...oh and sometimes they come out of the box with the float levels set incorrectly besides

 

[57fury440]

Edelbrock carbs do not need a lot of fuel pressure. The regulator may have been keeping the pressure where it needed to be for a good idle. The regulator should be after the fuel pump. Check to see if it is still there and if it has a gauge that can tell you what pressure you have. What volksworld said above is good advice.

 

[fury fan]

I had tons of trouble with an Edelbrock 750 AFB and saw other reports on the 'net that I was not alone. Reportedly issues with some geometry being scaled up from the 625cfm casting and not being correct. (I dunno)
After a year of fiddling with mine frequently (and I have a Wideband o2 gauge for feedback), I swapped to an 800 EPS (probably bigger than I need) and my problems went away.
That was 15-ish years ago, so the situation with that carb has hopefully changed.

If you have a stock-type mechanical fuel pump, you do not need a regulator.
If it's an high-perf pump, you'll need to verify the pressure rating.

Also check your fuel pump pushrod for correct length, if too short will definitely cause a fuel starvation issue at high rpm and/or speed.