Why is My Holley 847 Hard to Start?

If your Holley 847 carburetor is making your engine hard to start, it’s usually due to fuel delivery or mixture issues. Here are the main reasons and what to check:

Common Reasons Why a Holley 847 is Hard to Start

1. Incorrect Idle Mixture Setting

   • Too lean (not enough fuel) or too rich (too much fuel) can cause hard starting.

   • Fix: Adjust the idle mixture screws to the correct setting for your engine.

2. Float Level Set Wrong

   • If the float level is too low, the carb won’t deliver enough fuel to start.

   • If too high, it can cause flooding and hard starting.

   • Fix: Adjust the float level to spec (around 5/8 inch float drop). How To Adjust Float

3. Clogged or Dirty Jets and Passages

   • Dirt or varnish buildup restricts fuel flow, making starting difficult. If the vehicle has been sitting for months, the gas may have turned to varnish.

   • Fix: Clean the carburetor thoroughly, focusing on jets and fuel passages.

4. Weak or Malfunctioning Choke

   • A choke that doesn’t close fully on cold starts prevents proper fuel enrichment, causing hard start.

   • Fix: Check choke operation, adjust or replace choke components if necessary.

5. Old or Contaminated Fuel

   • Stale fuel or water in the fuel can cause starting problems.

   • Fix: Drain old fuel, refill with fresh gas, and check fuel filters.

6. Fuel Pump or Pressure Issues

   • Too low fuel pressure or weak fuel pump can starve the carburetor.

   • Fix: Check fuel pump and pressure; repair or replace if faulty.

7. Air Leaks or Vacuum Leaks

   • Unmetered air entering the intake can lean out the mixture and cause hard starting.

   • Fix: Inspect intake gasket, vacuum hoses, and carb base gasket for leaks.

8. Accelerator Pump Not Supplying the extra gas on a cold start.
   • Engine off, look down the carb and pump the gas. You should see a strong squirt of gas.
   • Fix: Main discharge may be plugged somewhere. Spray carb cleaner through the pump passage to clean it out.

Quick Troubleshooting Tips

• Start by checking and adjusting the idle mixture screws.

• Verify float level is set correctly.

• Test choke function by starting engine cold; choke plate should close fully.

• Inspect fuel quality and lines.

• Check for vacuum leaks using carb cleaner spray around the base and hoses; engine RPM changes indicate leaks.

Getting your Holley 847 to start easily is mostly about ensuring proper fuel mixture and choke operation. If you want, I can walk you through detailed adjustments or tests for any of these points. Just ask.