[Tom Vaught]

Had a few minutes so going to post up the other pieces of info I wrote years ago.

8) Adding weight to a black float:
You drill a hole in the black float, add the weight, do a trial measurement on the gram scale, and when you are close you add the light coating of epoxy to seal the whole deal up. I am NOT a big fan of people making the black float weight the same as the brass float as the black float dimensions are different vs the brass float. The Brass float has a longer arm therefore more force on the needle and seat vs the Black float weight.

9) Lean Acceleration caused by an improper float level setting:

As was mentioned in 5), if the float level drops too low, the “head” that the fuel has to overcome in the main-well gets higher and the engine calibration goes lean. If the fuel level is too high, the “head” that the fuel has to overcome in the main-well, will be much less and the engine runs rich. There is a “sweet spot” that was designed into the carburetor fuel calibration over many years of testing vs the parts used and random “experimenting” will typically cause issues over time.
High pressure boosting is adding another level of knowledge to this carburetor database of proper settings.

10) Why Bowl Vent Clearance is important: (Spoke about this earlier in the sticky)

The vent whistle at the top of the metering block was added to prevent fuel slosh out of the carburetor bowl vents. A Rivet typically holes it in place. There may be a slight leakage around the vent but typically it is there for fuel control in the bowl. Trimming the vent is commonly done. You do not want the fuel to slam against the back wall of the carburetor under acceleration, climb the back wall, hit the roof of the bowl, move forward, and then enter the vent whistle. A whistle about 1.25' long typically works well. I trim the opening with an exacto knife to allow more area through the vent whistle too.


11) “Sight Plugs” Why they are different Front Bowl to Rear Bowl and why some people have carburetor problems when swapping out Holley Bowls for after-market fuel bowls:

Few Holley bowls today do not have a “Sight Plug” but the location of the sight plug can be in several different locations. Primary bowls will always have a higher sight plug location vs the secondary bowl location. The number varies all over the map. The average bowl difference will be around .220” difference with some going over .300” difference. Why is this important? Because the sight plug location sets where the “bottom of the threads” location is that everyone sets their fuel level to. As said earlier, you do not want to screw up the Holley Fuel Level Calibration Setting Point if you can help it.

12) “How to use a Primary Float Bowl on the Secondary side of a Holley carburetor:

IF you put a Primary bowl on the secondary side of a carburetor you can typically set the fuel level to the bottom of the threads deal and the LOWER the fuel level 4 FLATS.

13) Float Bowl Screws can be different:

A stock Holley Metering Block type bowl screw is 63mm long from the metal surface the screw gasket seals against to the end of the screw threads. About 2.48” long. The Metering Plate Holley screw is about 48mm long, about 1.89” long. You will notice that neither of the screws is the standard 2” long or 2.5” long hardware store bolts. At one time there were some screws out there that looked the same as the Holley typical parts but they were VERY CLOSE to the 2” and 2.5” length dimensions. You use one of these screws in your carb you are almost guaranteed that you will strip a thread in the main-body as the screw will bottom in the casting, have no where to go, and any additional tightening will pull threads.

14) Never use “Hot Rod” needles and seats parts vs the “Holley Design” needles and seats:

Above in #13 we had a screw length issues that could cause problems. In this line we have a needle and seat thread issue that needs to be addressed. Holley needles and seats ARE as mentioned above a 3/8-32 thread. Some of the “hot rod” old style needles and seats were a bastard thread then therefore would strip out the threads in the float bowl after installation in the bowl. USE ONLY HOLLEY DESIGN TYPE PARTS.

15) Differences between Holley needles and seats:

Holley used a few needle and seat designs over the years. Initially Holley had steel needles and later offered Viton tipped needles for many applications. Holley offered several orifice sizes, with the .110” needle and seat being the most common. Holley also changed the feed strategy to the needle. The old units used drilled holes in the upper and lower chambers (typically 4 holes). The later generation parts used a “Picture Window” rectangular shaped entry hole for more flow to the carburetor bowls. Today we have the stock type needles and seats and also “Bottom Feed” type racing needles and seats.

16) Viton tipped needles and seats vs steel needles and seats:

Last but not least Viton Tipped needles and seats vs steel needles and seats. The Viton stuff seals very well unless you get metal chips stuck in the viton tip. A steel needle and seat will typically allow the trash if small enough to pass through the needle and seat to the bowl. Steel needles and seats are used on higher performance applications when using exotic fuel blends as the viton tip parts are designed for normal pump fuels and some racing fuels. Most alcohol carbs will use a steel needle and seat for two reasons: Increased orifice diameter required where the viton part is not offered and durability from the corrosive fuel.
The increased fuel orifice diameter requirement can be corrected bu the dual needle and seat strategy but the corrosive fuel issue is still there.

Tom Vaught