spstack

Hi all, I am getting ready to install a new 3810 on my 67 327/300 and would like to compare adjustments with those of you who have an optimised or stock setup (could be different!). My engine is stock and the new carb came with a red pump cam in #1 position. I have adjusted the WOT slack to .015 as recommended by many websites. Is this how it was set from the factory? Thanks!!!

spstack

I found some good information from Holley on setting accel pump...

ACCELERATOR PUMP:
The accelerator pump‘s purpose is to make up for the lag in fuel delivery to enable the engine speed to increase in response to throttle opening. Differences in vehicle weight, transmissions, and rear axle ratios affect the amount of fuel and the delivery rate that should be provided by the accelerator pump. This may necessitate the customizing of your accelerator pump to your vehicle and its use.
NOTE: The old saying —if a little is good, a lot is better“ does not apply to the proper tuning of the accelerator pump. Your car‘s performance
can be just as bad if it receives —too much fuel too soon“ as if it receives —too little fuel too late.“
Two factors that affect the accelerator pump‘s delivery is the pump cam and the pump shooter (discharge nozzle). The pump cam determines
the total volume of fuel and affects delivery rate; the pump shooter affects delivery rate and helps determine the duration of the shot.
In general, the #1 locations on the pump cams provide a moderate initial delivery and have a greater final delivered volume. The #2 locations on
the pump cams provide a greater initial delivery and have a lesser total delivered volume. The pump shooters have a number stamped on their
casting which designates the shooter size in thousandths of an inch, i.e., a #25 shooter has a .025“ discharge orifice. The smaller diameter
nozzles lengthen the pump shot duration and are used with heavier vehicles or with vehicles equipped with lower numerical rear axle ratios.
Larger diameter nozzles (.035 - .037) shorten the pump shot duration, but deliver a greater initial volume of fuel. These sizes should be used on
applications where engine speed will increase rapidly (vehicles with good power-to-weight ratios). Best acceleration is achieved when the
accelerator pump delivers the lean best power air/fuel ratio to the engine; not when the maximum volume of fuel is supplied.
An important point should be kept in mind when tuning a Double Pumper, the secondary accelerator pump must supply fuel for a sufficient time
so that the secondary main nozzles can —start up“ and deliver fuel to the engine after the secondary throttles are opened. If the nozzles do not
start by the time the pump shot expires, bogging will result. To apply the information above, follow these steps for tuning the accelerator pump.
Best starts or racing starts usually result when the rear tires break loose for the first 10 to 25 feet, this allows engine speed to increase rapidly to
get the secondary main nozzles started. If wide tires, which provide extremely good traction, do not permit the rear tires to break loose, bogging
can result. Best times may be recorded with narrower tires. This attention to tire size is not so important on vacuum operated secondary
carburetors since the secondary throttles will not open until the secondary nozzles are exposed to enough vacuum to get them started.
1.
Change pump shooters until the smallest diameter nozzle, which
provided the crispest response is found.
2.
Then change the pump cams and locations until the right cam is found
that provides even more response.
3.
Finally, change the pump shooter once again until the crisp response is
maximized.
NOTE: If a nozzle size is desired that seems —in between“ the nozzle sizes
provided, then the nozzle can be drilled to the desired size by using
a wire drill held in a pin vise.
4.
At this point, there should be no bogs, flat spots or black smoke
(indicating excessive richness) when accelerating at wide open throttle
from a standing start.

michaeliss

I too bought a new 3810 since I rebiult the original twice and still had problems. I have the '67 300hp 327 with powerglide. I bolted it on and there is a big difference in proformance. A got a lot more get up and go. I did adjust the carb idle but did not touch the pump.

JohnZ

Yes, but I always check it to make sure it's adjusted correctly, especially if the carb isn't factory-new out of the box; 90% of people mis-read the adjustment procedure and do it with the throttle linkage in the idle position instead of in the WOT position, and that always results in problems.