Carburetor Accellerator Pump Cams Video - Holley Carb DVD

[rotaxtwin]

Gotta love the adjustable nature of a Holley. It just rocks!

[swordfishmatador]

Ive got a huge problem. I have a 650 holley carbarator double pumper. A few weeks ago I ran out of gas snd the fuel filter and carbarator got covered in gook. I cleaned the filter and inside the carbataror bowls and still it wont stay running. What could be wrong?

[TheBlueToyota]

the jets up from the bowl may be clogged to have you checked them as well?

[swordfishmatador]

@TheBlueToyota Yeah I checked the jets as well. the problem was the front metering block. I changed it and it stayed running.

[VinnyMartello]

@swordfishmatador

Rip out the jets and dip them in some chem-dip or something.

[joness105639]

Always wondered what an accelerator pump looked like. My carburettors dont have one!

[BoxWrench]

You very likely do have an accelerator pump of some kind, it's design is probably just different from Holley's.

Without an accelerator pump shot of fuel, the engine will experience a brief hesitation at the moment your foot presses the gas pedal.

[joness105639]

"You very likely do have an accelerator pump of some kind, it's design is probably just different from Holley's"

Trust me, I dont have one one in either of my carburettors.

"Without an accelerator pump shot of fuel, the engine will experience a brief hesitation at the moment your foot presses the gas pedal."

Not so. Apparently you are unfamilliar with certain carburettors, just as I am unfamilliar with the type commonly found on american cars.

[joness105639]

By now, no doubt you either think I'm nuts, or you are curious how such a device could function. My carburettors use a variable venturi controlled by a piston which rises and falls in what is known as a dashpot. It has a single jet with a needle that fits into the jet and is afixed to the piston on the other end. Whn air moves accross the piston, a vaccum is created above it, causing the piston to rise. As the piston rises, it allows more air through the venturi and more fuel through the jet

[joness105639]

When you hit the gas, the piston rises but is slowed by a damper in the dashpot. Thus there is a smaller than usual venturi for the trottle position, and with faster air moving accross teh jet, the mixture become richer mommentarily. If one forgits to ensure that the damper is full of oil, the engine ill hesitate just as you said. This is the principle that SU, Zenitch Stromburh, and even some Hitachi carbs work on.

[BoxWrench]

Would love to see some video of the carbs and/or some graphics of the theory of operation...

Sounds like an interesting design. How is reliability and tuning?

[joness105639]

Tuning for more power? Not sure, never tried it. Tuning for good running is reletively easy. You have a mixture adjustment nut, an idle screw and a "fast idle" screw (the fast idle sets the idle speed when the choke is out. Once they are set, they dont need to get touched again for a LONG time. I'll send you a PM with the vids etc.

[DrFiero]

@BoxWrench : Can't believe nobody's touched on this in a year! The design above is a "CV" or constant velocity carb. Most bikes use the same principal. My 50's & 60's british cars also used them (SU carbs). They're very simplistic, and easy to setup and maintain.

There's a throttle plate near the manifold. A large'ish piston in the bore blocks about 80% of the opening. There's a metering rod attached to it. At idle, it stays down, mostly blocking air flow.

[DrFiero]

@BoxWrench : the metering rod mostly plugs the main jet. As you open the butterflys, manifold vacuum is metered to the top of the piston. It pulls it up, letting the piston rise, feeding more air and fuel, but only as the engine needs it (just like a vacuum secondary on a Holley).

[Maraud3r43]

just want to make use. there is no bog or hesitation off the line now but it bogs when i open the secondaties. i need a stronger secondary spring correct? also when my car is warm in park its idle is about 1500 and in driver drops to like 450, stutters a lil then goes back up to 600. how can i fix this? I didnt get a DVD with my street avenger :(

[heckeng1234]

When do you use the hole #2 in the throttle bracket? Is it whenever you use the cam hole #2 or #3? Do you ever use the #1 cam hole with #2 throttle bracket hole or vice-versa?

[BoxWrench]

Multiple holes in the throttle lever and in the accelerator pump cams allows you two tuning positions for each cam.

You would normally line up hole #1 in the lever with hole #1 in the pump cam. The same matching of the #2 holes as well.

This will allow you to match the profiles to the factory determined flow ratings and profiles designed for each accelerator pump cam.

[kreigsmann]

does a double pumper take double the fuel?

would i have to install a nother fuel pump?

[BoxWrench]

Double pumper does not mean that "double" the fuel is required at all times. It only squirts double the amount of fuel at the precise moment that the gas pedal is pressed.

The accelerator pump is only responsible for adding an extra shot of fuel to cover the lag in power when the carb swtiches from the idle circuit (engine at rest with no load) to the power circuit (engine under heavy acceleration). The accelerator pump smooths out the hesitation of mashing on the gas pedal and then shuts off

[kreigsmann]

hmmmmmmmmmmmm

i know i can look this up but...

my truck, 85 bronco 351 HO, needs a carb it has a stock holly 4180, could a double pumper be put in on this engine?...how much would it run for

[BoxWrench]

Go to Holley's website and run their Interactive Carburetor Calculator. If you have basically stock engine, use about 5000 as your max RPMs (not that you'd ever run that high but it's good for the calculation)

You'll find out that your small block engine won't really need a Double Pumper. You'll likely be best off with a "street avenger" in the 600 CFM range (model 4150 or 4160)

Double Pumpers are best on high reving engines with manual transmissions, Stock cars with auto trans don't need one

[PaisleyTelePlayer]

i have a 71 nova with a mild 327, weiand intake, and a model 4160 holley carb. i had changed the discharge nozzels, the jets, adjusted the floats, everything! but the carb still stumbled and bogged alot on acceleration, and cruzing speeds. so i decided to spend $20 and get the holley accelerator cam kit from summit. i changed my cam from the orange one to the green one and it made a hell of a difference! my carb runs perfect now! if your having the trouble i was, just change the accelerator cam.

[BoxWrench]

Tuning Accelerator Pump cams is one the absolute best way to adjust behavior of the engine at the moment you step on the pedal, but it doesn't affect any of the other aspects of the carbuertor and it's additional fuel circuits.

This is why we made the Holley carb tuning DVD. It covers all of the fuel circuits and all of the accessory kits you can get to tune every aspect of the Holley carb.

People with Edelbrock and other brands of carbs will be able to apply much of the theory as well...

[MRSLANDER530]

thnk you i will do it in my grage