i`ve played with this for quite sometime now, finally got it. first of all, my engine is ONLY a 355, 465/488 lift, 244 duration cam, about 10/1 compression, 491 heads, 650 carb. nothing out of the ordinary. so, i never thought that i would have to use one of the other holes on the accelerator pump. i even drilled the "squirters" a little bigger, but to no avail. after different metering rods, drilling the squirters, mixture screw adjustments, jets, just for the h*** of it i move the rod, closer to the carb. BAM. works great. what i`m getting at, with my little engine, i never thought that i would have needed to adjust/move the pump rod. could the carb be to small? just thought i`d post my findings. don`t want to bore anyone. thanx.
OFF-IDLE STUMBLE, EDELBROCK CARB
2 reading
hddude
1 - 15 of 15 Posts
i`ve played with this for quite sometime now, finally got it. first of all, my engine is ONLY a 355, 465/488 lift, 244 duration cam, about 10/1 compression, 491 heads, 650 carb. nothing out of the ordinary. so, i never thought that i would have to use one of the other holes on the accelerator pump. i even drilled the "squirters" a little bigger, but to no avail. after different metering rods, drilling the squirters, mixture screw adjustments, jets, just for the h*** of it i move the rod, closer to the carb. BAM. works great. what i`m getting at, with my little engine, i never thought that i would have needed to adjust/move the pump rod. could the carb be to small? just thought i`d post my findings. don`t want to bore anyone. thanx.
Joined
·
15,471 Posts
I had the very same problem with a 750 CFM on a 468. I never did fix the problem after hours of changing springs,metering rods and jets and accelerator pump settings. I finally gave up. I am glad to hear you succeded.:tu:tu:tu
Joined
·
377 Posts
I can't speak to the Edelbrock, but on the Holley look at three adjustments: Power valve may be rated too low in inches before it opens...this is the key transition element in the Holley...second, change the accelerator pump cam for a bigger, earlier shot....and three, install a larger capacity squirter.
Don't do as I have done and make all 3 adjustments at once. Rather, go cam first, PV second and squirter third.
If the motor seems to hesitate, then picks up rpm quickly, it's generally a starvation issue and more fuel is necessary. If it stumbles and coughs, then cleans out, you've got too rich a condition and need to lean the mixture out (smaller pump cam, lower rated PV, quicker opening of the secondaries).
When the bog/stumble occurs post full throttle, a lighter spring on your vacuum diaphragm will allow a quicker opening of the secondaries.
Lastly, double check the rate of advance in your distributor. Not enough lead will cause a bog. On my 383, and the little 331, it's at a full 36 total at 2200 rpm.
Once you get a Holley dialed in on the transition from idle/low rpm to full throttle you can concentrate on jetting but not before.
paul
My only experience with an Edelbrock was that I needed bigger squirters. Pump linkage didn't seem to make much difference. But who knows? Maybe it was put together in the wrong configuration. On mine I could have gone the wrong way, so if it was in that "wrong" position, it would have needed to change.
Holleys can respond well to bigger squirters too.
Another aspect of tuning this same problem is ignition timing. The more initial timing the better, until you get into pinging, or hard starting when the engine is hot. In fact, you should try the timing deal before you try squirters for the carb. But you may need both.
Holleys can respond well to bigger squirters too.
Another aspect of tuning this same problem is ignition timing. The more initial timing the better, until you get into pinging, or hard starting when the engine is hot. In fact, you should try the timing deal before you try squirters for the carb. But you may need both.
Joined
·
1,547 Posts
typically
stumble or bog is NOT from too small a carb, usually from to large a carb.
to large and the velocity slows down causing lean condition and poor atomization.
to cover up bog , extras fuel must be introduced.
usually from accel pump, ( squirters or pump lever)
I would look a timing first, and vac advance, both can cause bog or stumble.
stumble or bog is NOT from too small a carb, usually from to large a carb.
to large and the velocity slows down causing lean condition and poor atomization.
to cover up bog , extras fuel must be introduced.
usually from accel pump, ( squirters or pump lever)
I would look a timing first, and vac advance, both can cause bog or stumble.
Joined
·
1,418 Posts
i'm having similar issues with my carter afb 750. moving the rod to the hole closer to the top changes the rate of the squirt, not the volume. need to bend the linkage rod to incease the stroke of the pump to increase the volume.
Joined
·
1,418 Posts
first thing i did was lose the tiny clip and replace it with a clip that could be removed and replaced with my fingers instead of a needle nose pliers
![Image]()
RICK`S, well, if that`s your carb, you`re in the wrong hole to start with. it should be in the middle hole from the factory. just put it in the top hole and try it. that`s what worked for me. besides that, i drilled the squiortes bigger. you have less fuel going in, with it set like the picture.
Joined
·
1,418 Posts
i tested all three holes, and bent the rod for each hole position for maximum volume with a 0.5" pump stroke. the holes change the rate and slightly the volume if the rod is not bent as well. i am measuring the results by the length of the burnouts in front of my house :sign0020:
Joined
·
1,418 Posts
my sunshine prefers a long duration squirt. she gags on all at once squirts :sign0020:
1 - 15 of 15 Posts
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
