Attaching Early GM Throttle Linkage To Holley Carbs
There are various types of throttle linkages on early GM cars that attach
differently to a Holley carburetor. Here are some tips to attach a variety
of GM model throttle cables with different transmission applications.
How And When To Change The Jets On A Holley Carb
Holley explains how the main jets on a four-barrel carburetor operate. They
also give instructions on changing the jets for increased performance. The
video explains the various jet sizes, and how they affect engine
Holley Carb Troubleshooting and Rebuild - Things to Check!
Did some more troubleshooting on the carb. Found a few major issues.
1. The primary float bowl float was not adjusted correctly and was not
shutting off the fuel. The tab on the float was bent down allowing the
float to travel all the way to the top of the bowl without seating the
needle. This allowed fuel to continually flow into the carb and richen it!
2. The power valve was the wrong size. According to Holley, the valve
should be 1/2 the measurement of vacuum at idle in drive. According to my
vacuum measurements, the power valve installed was opening too soon and
dumping raw fuel in the engine when it was not ready for it, again
richening the mixture!
3. The idle mixture screws were not set correctly. They were at 2-1/4 turns
out. That is too rich for this particular engine setup. Using a vacuum
gauge, I adjusted the idle mixture for maximum vacuum at idle. In my case,
that was 1-1/2 turns out which is also the recommended Holley starting
4. My vacuum advance was not connected to the right port. It was connected
to manifold vacuum instead of ported vacuum off the carb. This caused the
timing to always be advanced at idle and then retarded under load as
manifold vacuum drops under load! Totally backwards! Ported vacuum on a
Holley can be found above the idle mixture screw on the passenger side of
the carb at the metering block.
I bought this carb about 10 years ago as a "store return". I didn't do much
to it then, assuming it was fine . I just bolted it on and drove the car,
seemed fine then. I realize now that the temporary owner messed with the
float and bent the tab too far and he also changed the power valve. I am
checking online to see what the stock main jets should be as he might have
changed those too! Word to the wise, never take anyone's word for it that a
carb is "all set to go!" Each application is different depending on the
vehicle and the amount that the engine is built. Use the proper tools like
vacuum gauges and look up tables to adjust for the proper values for your
application. There is no one size fits all!
Final word about power valves. Holley has built in an anti-backfire check
valve circuit in all Holley carbs since 93. Blowing out a power valve by
backfire is nearly impossible. However, the diaphragm can get old, cracked,
and brittle so it is best to pull it and examine it if you suspect it to be
a problem. To test it, turn all idle screws in all the way while the engine
running at idle. If the engine stalls, the power valve is working properly.
(keep track of the number of turns so you can put them back where they
I did complete rebuilding the carb and reinstalled it. I will have more
video of making adjustments and test drives soon...Thanks!!
Holley Carburetor Performance Tune - Summit Racing Quick Flicks
Norm covers all of the tips to get the most out of your Holley Performance
Carburetor. He covers how to tune your Holley Carb for high horsepower and racing
applications. He even goes over advanced power valve and jet tuning for
the Holley Carburetor.
Carburetor vs Fuel Injection - Summit Racing 101
What is the difference between a carburetor and fuel injection? Listen as
Dave guides you through 2 barrel carbs, spread bore carbs, race carbs and
compares them to EFI.
To check out Summit Racing's selection of carburetors, click here:
For Fuel Injection EFI systems, click here: