Holley 852 Carburetor Troubleshooting

Sluggish engine responses. Very little fuel coming out of the main discharge.

This could be cause by a bad pump inlet check valve, which in this case is a check ball at the bottom of the pump well.

With pump discharge nozzle removed, hold the pump discharge needle with your finger and pump the throttle. If the inlet check ball does not seat, fuel will bubble back into the float chamber from the pump inlet passage. Replace the pump inlet check ball. Stake the ball into the seat with a brass drift punch. Not too hard. It doesn’t take much.

Continual discharge from pump discharge nozzles at higher speeds.

Could be caused by a bad pump discharge needle valve.

Check the pump discharge needle and its seat for damage or foreign matter which would prevent the needle from seating properly.

Replace the check weight needle. Install in the discharge hole and using a brass drift punch tap the check weight so that it forms a good seat. Make sure the weight is loose when done.

Mixture too rich, or too lean, resulting in sluggish operation.

May be improper main jets.

Are you operating over 5,000 feet. Standard installed jets are good for below 5,000 feet. If so, reduce the size of the jets by .002.

Are spark plugs black? Reduce the size of jets by .002.

Are spark plugs white? Increase the size of jets by .002

Plugs should burn a gray color.

Rough running engine from over rich fuel mixture and warm up. Black exhaust, fouled plugs.

Possible excessive choking.

Check choke linkage for binding or damage. Check for freedom of action of poppet valve on choke plate. When idling check for vacuum leaks around the carburetor and intake manifold.

Rough Idle

Idle mixture screws might be out of adjustment.

Connect a vacuum gauge to the carburetor and turn the screws in or out to get the best vacuum.

Inspect the idle mixture screws. There should be no scoring on the tapered end.

Idle Adjustment Screws Don’t Change the RPM

Might be loose or damaged idle tubes, clogged air bleeds, or restricted idle fuel passages.

Make sure these are all clean and passages are clear.

Poor or Low Speed Operation

Make sure both idle mixture screws are equally adjusted. If one needs to be turned in more than 1/4 turn more than the other screw, then you have a problem as described above.

Idle transfer holes may be clogged or damaged. Remove, inspect and clean.

Bad Acceleration

May be continual discharge from the pump discharge at higher speeds.

Check for worn, distorted, or damaged pump piston.

Updated on 12/16/2020

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