View Full Version : 390 fuel pump noise

04-22-2014, 09:58 PM
Hi Just noticed a noise coming from what I think is my fuel pump on a 65 390 engine. Using a stethoscope I checked on top of fuel pump in diaphragm area and had the loudest noise a steady clunk, clunk, clunk anyone ever run into this?

04-22-2014, 11:44 PM
The fuel pump is mounted with just two bolts. Take them out and inspect the pump arm. Look for scoring or anything that might have broke. This is an easy thing to inspect. If it looks and feels ok, put it back in.

I have never had a fuel pump emit loud noises, but the timing set components behind the water pump can if something is coming loose. It is good that you are investigating early warning noises. I hope you find the problem soon. - Dave

04-27-2014, 08:05 PM
It seems I can hear a noise from the fuel pump. I used a stethoscope and I hear a steady clunk, clunk, clunk..... coming from the diaphragm area of pump anyone ever come across this? Also I noticed a stumble in acceleration of engine. Thought Id check fuel bowl level which looked OK. Noticed air bubbles coming from under float I think it was coming from main jets what would cause this?

04-27-2014, 08:32 PM
The pump is powered by an eccentric circular lobe at the front of the camshaft. A spring loaded steel lever from the pump contacts the circle, and the circle cycles the lever at camshaft speed. They are always in contact.

I've never listened to one before, but if it's loud then my guess is the spring is broken or weak and the constant contact is lost and you're getting a slapping action instead.

The replacement pumps are less than $35, but like everything else these days, cheaply made in China. So bench test the new one before you install it. I have installed two in different cars over the past 6 months and both have been defective.

04-27-2014, 08:35 PM
If the pump is "slapping" and somehow getting air bubbles into the float bowl it could cause stumbling. Or it could be your accelerator pump diaphragm. If you haven't rebuilt the carb in ten years, it's time to do so.