I've been having some rough off idle acceleration problems and haven't been able to pinpoint the culprit. The engine was rebuilt before I bought some years ago so its always a little more difficult to know what they did or didn't do to the engine. I've tried a new Edelbrock 94 carb and a rebuilt Holley 97, and replaced everything including the power valves and the accelerator pump ***embly, but nothing seem to help. I did replace the points with an Igniter system for a 6V positive ground system and it seems to idle pretty good and the timing is on the dot or 2 degrees BTDC. The fuel pump puts out a steady 4 1/2 psi. I have also replaced the coil, wires, plugs and cap and rotor but it still accelerated rough. Any thoughts? I thought accelerator pump first but I've checked and replaced it and no change. Thanks in advance for any insight into this issue!
You replace the power vales but did you replace them with the correct ones or just new ones? Also do you have weak valves? Have you had the heads off or done a leak down test?
I checked for vacuum leaks around the carb and manifold but nothing. I even replaced the vacuum canister on the distributor. I rebuilt the carb with a factory type rebuild kit but they did not say what size the PV were in the kit the way new Holley's do on the side. I also rebuilt the fuel pump that was on the truck and finally put a pressure gauge on it last night and at idle the engine sits at 19" of vacuum and 4 1/2 psi. of fuel pressure but it can't get out of its way during off idle acceleration. No tach but the idle is very low.
Sorry, I have not had the heads off yet, but a cylinder leak maybe the next choice in trying to solve this issue. I am also running a factory vacuum distributor with the Igniter electronic conversion kit. Thanks again!
The 6 Volt Petronix units have a bad reputation. I would try conventional points and condenser. Cheap experiment and you've tried about everything else. By the way pull all the plugs and see if all the cylinders push your finger out when you plug up the hole and spin the motor. I'm ***uming you don't have a compression gauge or leak down checker.
To me that sounds like an accelerator pump problem, if it really falls on its face when accelerating away from idle. You said you put in a new pump, but did you maybe overlook a spring and/or check ball somewhere during re***embly? Can you see if it's got a good steady accelerator pump stream when you crack the throttle open?
Suspect that you do not have advance happening right off idle. late ('49-53) flathead has weak advance and probably not enough initial advance at 2 degrees. Probe this with a short test...for this test, since there is a possibility of too much top end advance, run the thing only through the low engine speed range whre the trouble happens and do not go up to road speeds. Just reset the initial timing to substantially more advance and go for the brief test drive. If problem improves, the stock distributor and settings need to be tossed. If no change, start focusing on idle and off idle circuit in carb after putting your timing back to stock... I'm ***uming stock distributor here...which leads to more questions, too...if you ran it with a 97 you either had NO advance if unhooked, or totally fubar advance if you hooked it to manifold vac...so is this the original distributor, and what are you doing with the vac line????
I thought the PSI was a little high too but that's what she read. I did change the accelerator pump, but not the ball. I did a basic check and it appeared to give a good shot and it did not appear to push fuel back into the carb bowl. I may take it out and change it just for the sake of knowing that it has been changed. It is the stock distributor with the Pertronix 6V Positive ground kit. I plugged the vacuum port on the back of the carb before I timed it. Funny, at idle RPM the timing didn't change after I hooked the vacuum line from the distributor back up.
The "****" they call gas now a days is a possibility. Are you running fresh (ethanol free) gas ? VR&C.
The igniter is irrelevant on stock distributor...generally advances poorly at best, and it sounds like this one is not advancing at all. Remember, its advance is related to load and not directly to RPM, so revving it in neutral is NOT going to show same advance as running it on the road.
Listen to Bruce, he knows. A distributor upgrade is the single best thing you can do for a late flattie V8.
Went through the same thing Bruce described. I rebuilt my carb, new coil , plug wires, plugs, timing right in the sweet spot, still ran like ****. I got a distributor from Jim Linder, aka Bubba Put in new dizzy and runs like it should now.
Proper adjustment for stock Loadamatic for hotrod use: Place on anvil or sidewalk. Adjust with large hammer until it fits into an 8X11" manila envelope. Send it back to Holley for adjustment...their service address is: C/O Dead Letter Office Fargo, North Dakota Install an early Mallory or a Chevy conversion to keep the heap running until the original distributo returns.
I was digging through an old parts box last night when I was looking for a spare distributor and I found two! The first was a stock Ford and the other, buried under all the grit and grim, was a Mallory YC275 dual point distributor. I am going to try to make the dual point work because its got that cool old school look. Stay tuned... I am running pump gas with 91 octane, but I think everything has some ethanol in it these days right?
Okay, I finally got back in the garage and found something I quite don't understand. The fuel would bounce between 4 1/2 and 6 1/2 psi and them all the sudden I saw it kill my 15 psi fuel gauge when the needle buried itself. I tried another fuel pressure gauge and it tried to kill it too. The engine was only idling about 450 RPM. I replaced the fuel pump and it stayed right at about 5 to 6 psi and the engine idles and accelerate perfectly.
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