Carb Woes

[Mike Bucher <mbucher@domain.elided>]

I have posted this here before, but the lean stumble subject keeps coming up.

I chased this one for years, wasted lots of $$. Carb overhaul, nope!, New
carb, Nope! Adjust the timing. nope!

Those people that tell you it is the accelerator pump are close, the pump
is ok, but you are not getting enough gas out of the shooters fast enough,
hence the stumble or stall when coming off idle.

As for your cold motor experience, I suspect that this is before your
automatic choke opens all the way and you are running rich or you have the
manual choke out partially.  I have manuals on my vehicles.

Interesting note on my vehicles, the 266 has never had the problem, the 304
always had.

My neighbor mechanic remembers that Ford ran the Holley on their pickups
and came up with a replacement shooter that had larger holes.  If you have
any old time Ford partsmen acquaintance you might ask them.  I also
discussed this with a school bus mechanic, he said the same thing.

Drag racers also ran into this problem and found the fix.  If you have a
Holley carb book, they address it somewhat, but you need to read between
the lines.

So now for the fix:

The accelerator "shooter" is the little device you see the gas shoot out of
when you pump the gas and look down the throat of the carb.  It is held in
place with a large phillips head screw.  Gasket top and bottom.

The holes in the shooter on my carb were .031 inch.  I think the number is
stamped on the body.  

I made a little spread sheet to calculate the increase in area of the holes
from stock to 100% oversize (area wise):

Diameter    % Increase
.031		Stock
.032		6.56
.033		13.32
.034		20.29
.035		27.47
.036		34.86
.037		42.46
.038		50.26
.039		58.27
.040		66.49
.041		74.92
.042		83.56
.043		92.40
.044	      101.46 	

I drilled the first oversize at  .038 (50% area increase) and road tested
it.  Definite improvement, but a little stumble.  Pulled back in front of
shop and removed shooter and drilled at .041 (75% increase) and road tested
it again.  Barely a stumble.  That is where I have it now.  When I get
around to buying a couple more wire drill bits, I will fine tune it.

You get the drill bits from hobby shops.  I got mine from a model train
shop.  Get the little pin vice to hold the bits.  You don't need to put
them in a drill, just use your fingers to spin the pin vice.

Anyone try this?  Did it fix your problem?