• Dual Fuel LPG Carburetor - Model 425

4bbl Off-Road Dual Fuel LPG Carburetor Kit


  • Pre-1987 Domestic Engines with 4bbl carburetors
  • Small block and big block V8 engines
  • Large vehicles such as pickup trucks
  • Off-road use only

Model 425 Mixer

  • Adapter to suit carburetors with 5-1/8" air horn
  • Overall height of mixer assembly above the carburetor's airhorn is 4-1/4" high - measure for sufficient clearance before ordering!
  • Mixer flows 460 CFM @ 1.5" Hg
  • Single fuel inlet

General Information

  • Ignition timing should be optimized for propane operation
  • Compression can be increased to take advantage of propane's 104 octane rating
  • Components in package may differ from those shown in pictures
  • Recommended for applications up to 350 hp
  • Fuel mixture controller may be added for closed-loop operation

Components Included in Kit

  • 1 Impco CT425M-2 Model 425 Mixer, Silicone
  • 1 Gann AA9-54 Adapter, Right-angle mounting of CT-425 on 5-1/8" air horn, 4-1/4" high
  • 1 Impco F1-15 Filter, Element 400CFM
  • 1 Impco C1-28 Air Cleaner Lid for F1-15 filter
  • 1 Gann 88EN Vapour Elbow, Nylon, 1" Hose x 1" MNPT
  • 1 Gann 5596-R Switch, Dual Fuel, 3 positions, on-off-on, 6 spade lugs
  • 1 Rochester 5-2063 Sender, GM, for 0-90 ohm fuel gauge
  • 1 AFC 121 Gasoline Fuelock, ¼" FNPT inlet & outlet

Components NOT Included in Kit

  • Fuel tank
  • Fuel line from tank to fuel lockoff valve
  • Remote fill valve (if required)
  • Fuel Gauge
    • Use GM 0-90 ohm fuel gauge
    • Or connect to vehicle fuel gauge through toggle switch
  • Fuel Line Adapters (buy locally depending upon your fuel line):
    • Fairview 68-5B Gasoline Fuelock adapter, ¼" MNPT x 5/16" tube compression fitting (2 required)
    • Fairview 68-6B Gasoline Fuelock adapter, ¼" MNPT x 3/8" tube compression fitting (2 required)
  • Basic Components Package. To make an underhood conversion kit, you must add BCP-EE Components kit.

System Operation

  • Vehicle runs on gasoline exactly the same as with unmodified vehicle. Gasoline fuel economy may be slightly lower.
  • To switch-over to LPG, the carburetor must first be emptied of gasoline. This requires you toggle the switch to OFF position where both fuels are shut off to the engine. This is best done while stopped in a safe location.
  • When engine begins to stumble from lack of gasoline in the fuel bowl, toggle the switch to the LPG position. When the engine begins to idle smoothly, it is safe to begin driving while running on LPG.
  • It is best not to run out of either fuel but if you run out of LPG, you must stop the vehicle in a safe location, toggle back to the gasoline position, and crank the engine (assuming you have a mechanical fuel pump) until the engine starts. If you have an electric fuel pump, you may instead let the pump run for a minute to refill the carburetor before restarting.

Ignition Timing

  • For best fuel LPG economy, the engine's timing advance curve should be optimized for LPG. While not optimal for gasoline operation, you should only be running on gasoline long enough to keep the fuel from becoming stale.
  • Many vehicles do not have readily available timing re-curve kits any more. You may want to consider converting to a fully programmable dual map ignition system such those available from Autosport Labs.

Dual Fuel LPG Carburetor - Model 425

  • Brand: Impco
  • Product Code: LPGCARB-425-DF
  • Availability: 10
  • $482.00

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