Description
Product Overview
The iFJF 1801 Thunder AVS 500 CFM 4-barrel carburetor is purpose-calibrated for small displacement V8 and V6 engines. With annular discharge boosters, electric choke, and the signature Thunder AVS tunability, this carburetor delivers crisp throttle response and excellent driveability on engines from 260 to 327 cubic inches. Perfect for street rods, compact V8s, and mild cruiser builds.
Key Features
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500 CFM — Right-Sized — Properly sized for smaller displacement engines (260-327 CID). Avoids the low-speed drivability issues caused by over-carbureting with larger 600-750 CFM carbs.
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Electric Choke — Automatic 12V electric choke provides hassle-free cold starts. Heats up in 1-2 minutes and opens progressively — no manual cable to route.
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Annular Discharge Boosters — Eight-hole booster rings deliver superior fuel atomization at low airflow rates, critical for small engines that spend most of their time at part throttle.
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Tool-Free Secondary Tuning — Change secondary metering rods in seconds through the top of the carburetor. No disassembly required.
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Aluminum Body — Lightweight, corrosion-resistant, and runs cooler than cast iron. Factory pre-calibrated and wet-flow tested.
Compatibility
| Engine |
Displacement |
Application Notes |
| Chevy Small Block |
262, 267, 283, 305, 307 |
Best for mild-cam street engines |
| Ford Small Block |
255, 260, 289, 302 |
Ideal for Mustang, Falcon, early F-100 |
| Buick V6 / V8 |
231, 252, 260, 300 |
Fits square bore intake manifolds |
| Chevy V6 (4.3L) |
262 |
Requires 4-barrel intake manifold |
| Jeep V8 |
304 |
Good match for CJ and Wagoneer builds |
Specifications
| Parameter |
Value |
| Part Number |
1801 |
| CFM Rating |
500 CFM |
| Barrels |
4-Barrel Square Bore |
| Choke |
12V Electric Choke |
| Booster Type |
Annular Discharge |
| Primary Jet |
0.086" (factory) |
| Secondary Jet |
0.092" (factory) |
| Body Material |
Die-Cast Aluminum |
Why 500 CFM?
Small engines don't need big carbs. A 305 with a 750 CFM carb will have sluggish throttle response, poor fuel economy, and a weak vacuum signal that makes tuning impossible. The 1801 is designed and calibrated specifically for 260-327 CID engines. You'll get crisp off-idle response, stable idle, and excellent part-throttle manners — the things you actually feel when driving.
Frequently Asked Questions
Q: Is 500 CFM enough for my 305 Chevy?
A: Yes. A 305 at 5,500 RPM requires approximately 485 CFM at 100% volumetric efficiency. The 500 CFM rating is ideal — it provides enough airflow without the sluggish low-speed response of an oversized carb.
Q: How do I wire the electric choke?
A: Connect the choke's positive terminal to a 12V ignition-switched source (only powered when the key is ON). Do NOT connect to the coil positive terminal. The choke housing grounds through the carburetor body.
Q: Can I adjust the choke?
A: Yes. Loosen the three screws on the choke housing and rotate it to adjust the opening rate. Turn toward "rich" (clockwise) for slower opening in cold weather; toward "lean" (counterclockwise) for faster opening in warm climates.
Q: Will this fit a 2-barrel to 4-barrel conversion?
A: Yes, as long as you use a 4-barrel square bore intake manifold. You cannot bolt a 4-barrel carb to a 2-barrel intake without an adapter (not recommended).
Q: Is this carb compatible with EGR?
A: This carburetor does not have EGR provisions. It is designed for non-EGR applications or vehicles with EGR systems deleted (for off-road/racing use only).
