Specifics about setting accelerator pump?

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LovetheA's

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Afb carb correct for 67 383 4 speed a body. Motor never been rebuilt so stock performance. I cleaned and rebuilt the carb and still having some problems. I set floats to factory specs. Installed new jets. primaries are set to stock secondaries 1 step up. Metering rods are factory specs installed new springs slightly taller slightly stiffer. I think this would be less efficient at cruise but better for power phase. Ok with that. I have read all the posts about bogging at hard acceleration on takeoff. It still didn't answer my questions. My car bogs for split second at hard acceleration under load only. When in neutral throttle very responsive. Rod for accelerator pump is set at middle hole. Is my problem accelerator pump and if so too much fuel or too little at takeoff? Let car idle in neutral checked function of accelerator pump when blip the throttle under the hood. Nice squirt from both sides doesn't seem to be much delay. Should I try slightly bending rod to accelerator arm to take out any possible slack or readjust rod to lower or upper hole. Don't know what's going on?

Carl
 
Just a couple of thoughts, and I'm far from a carb guru, lol.

Did the carb have a leather AP?

Is the "S" linkage installed correctly?

Sometimes the old leather pumps work better if they are salvageable, they can be cleaned, oiled and re-used (sometimes).


LovetheA's said:
Nice squirt from both sides doesn't seem to be much delay.
Click to expand...

There should be NO delay. With the bowls full, shut the engine off, get a good flashlight, look down in the carb and blip the throttle, you should see an INSTANT shot of fuel. If you aren't getting that, you can try gently adjusting the linkage rod so the arm for the pump moves sooner.
 
Bad Sport said:
Just a couple of thoughts, and I'm far from a carb guru, lol.

Did the carb have a leather AP?

Is the "S" linkage installed correctly?

Sometimes the old leather pumps work better if they are salvageable, they can be cleaned, oiled and re-used (sometimes).




There should be NO delay. With the bowls full, shut the engine off, get a good flashlight, look down in the carb and blip the throttle, you should see an INSTANT shot of fuel. If you aren't getting that, you can try gently adjusting the linkage rod so the arm for the pump moves sooner.
Click to expand...

Badsport

Yes the replacement accelerator pump from Mikes Carbs is just like the old one with a leather wrap. Also the s clip is installed correctly looks like an s from the front. I still don't know if adjustment of the accelerator pump down or up will remedy the bog under load. Does the hesitation occur from too much fuel or to little?
 
This linkage design didn't push the pump rod straight down. Over the years of usage, the pilot hole in the carb wears allowing the pump shaft to rock or lean before downward movement begins.
How much wear you have there or how much is too much ? I don't know. I only know there is some lost motion there.
Vacuum advance is a player in off idle response too. With my base timing jacked up to 16 btdc I had to back off the idle rpm at the carb. So the linkage position changed a tad too.
I get a lot better throttle response / performance in general with the vacuum advance disabled.
That may not be your solution. Easy enough to rule it out.
 
With a stick-car, you sometimes need to slow the secondary air-door.
If the secondaries open too fast, it will bog no matter what you do. This gets worse with the smaller gears like 2.7s. With 4.1s it is less of an issue. This is why I have a Holley-DP carb; the secondary has it's own pump.When I whack the pedal,things happen in a hurry!
If you have a big cam and low compression, then engine vacuum will be correspondingly low. Low vacuum means the low-speed circuits will have a hard time coming up to speed.
If your timing is late, the vacuum will be lower than it could be.
If you cylinder pressure is down, your vacuum will be down.
If the exhaust system is restrictive,as in nearly plugged, then the hot exhaust cannot get away fast enough to let the fresh cold air in.
If Hillary dies the day after she gets elected, who steps into her shoes?
For comparison;
Ok so Say you have 10.5 Scr and a 220*cam with the usual bolt-ons,in a 3100 pound Dart, plus at least 3.55s, and are running at least 16* of initial timing, and you are not dumping the clutch too early. This is a tire-fryer.
But if your Scr is stock,with a 240* cam,12*initial, and you have 2.76s, and a 3800 pound tank; well you are gonna have to slow things down.

So I read you have a 67-A, on the original engine.Is it running all original ? Including the factory manifolds,pipes, mufflers and air filter housing?And the factory hi-way gears?
If you hit a wall with this, might I suggest a compression test, a cylinder leakage test,and a timing chain stretch test.
But to recap; if the problem is strictly on take off, I would suspect the accelerator-pump circuit.
Good hunting...
 
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