A Rochester 4-Jet carburetor failing to start can be attributed to various factors. Let's explore some common reasons why your Rochester 4-Jet carburetor-equipped engine might not start:

1. Fuel Supply Issues:
   • Check if there is an adequate supply of fuel to the carburetor. Ensure the fuel tank is not empty and that the fuel lines are not clogged or blocked.
   • Verify that the fuel pump is functioning correctly and delivering fuel to the carburetor.
   • Inspect the fuel filter for any clogs or restrictions that might impede the flow of fuel.
2. Choke Operation:
   • Ensure that the choke is operating correctly. A stuck or improperly functioning choke can prevent the engine from getting the necessary air-fuel mixture for starting.
   • In cold weather, make sure to engage the choke to enrich the air-fuel mixture for easier starting.
3. Ignition System:
   • Check the ignition system components, including the spark plugs, ignition coil, distributor, and spark plug wires. Faulty ignition components can lead to a no-start condition.
   • Confirm that the timing is set correctly. Incorrect ignition timing can hinder the engine from firing up.
4. Carburetor Issues:
   • Inspect the Rochester 4-Jet carburetor for any blockages, clogs, or internal damage. Over time, carburetors can become dirty or suffer from wear and tear.
   • Look down the carburetor after turning the engine off. If gas is dripping down the venturi then gas is probably getting siphoned into the engine, draining the float bowl dry.
     • It could the check ball is not seated in the main discharge, or the spring above the check ball is missing.
     • A non vent gas cap is being used. It must be vented.
     • The float bowl vent is blocked off.
   • Ensure that the carburetor is adjusted correctly. Incorrect settings can affect the air-fuel mixture and, consequently, starting.
5. Air Intake:
   • Check the air filter to ensure it is clean and not obstructed. A clogged air filter can disrupt the air supply to the carburetor.
   • Ensure that there are no vacuum leaks in the intake manifold or vacuum lines.
6. Compression:
   • Verify that the engine has proper compression. Low compression in one or more cylinders can make starting difficult or impossible.
7. Fuel Quality:
   • Ensure that the fuel being used is of good quality and has not deteriorated over time. Stale or contaminated fuel can lead to starting issues.
8. Mechanical Problems:
   • Investigate for any mechanical problems within the engine, such as a seized engine, damaged components, or excessive wear.

If you have checked these common issues and your Rochester 4-Jet carburetor-equipped engine still refuses to start, it may be beneficial to consult a qualified mechanic or automotive technician for a more in-depth diagnosis and repair. They can perform a thorough inspection and address any specific issues that may be preventing your engine from starting properly.