Got the new fuel pump and pressure gauge installed. Results not as expected....

[RECHRGD]

Finally got out to the shop and installed the new Carter 6903 mechanical pump installed along with a new Jegs liquid filled pressure gauge.  I bought this pump because I wanted to eliminate the regulator that the previous pump required.  The new pump is advertised to run between 5.5 and 6.5 pounds.  The old gauges' needle bounced so much that it was useless.  The new gauge reads about 3 pounds at idle and peaks at about 5 pounds.  From everything I've read, that is too low for a Holley 750 DP.  The filter is also new.  The new gauge has a "purge" button on it, but pushing it did nothing.  Any ideas other than a bad pump?  As the old saying goes, "if it ain't broke don't fix it...

[WHITE AND RED 69]

Worn fuel pump pushrod?

[RECHRGD]

Worn fuel pump pushrod?

It was working normally when I put it away last fall.  However, I didn't measure it when I easily could have while doing this little chore......

[c00nhunterjoe]

I do not like liquid filled fuel pressure gauges. The reading varies greatly with temperature even with the purge buttons. I suvgest a standard gauge. Almost all mechanical pumps ive used will bounce the needle. That is normal because of the cam activation.
Last liquid gauge i tried showed 6 psi on initial start and 3 psi at op temp, with a purge button. Aeromotive pump

[RECHRGD]

I do not like liquid filled fuel pressure gauges. The reading varies greatly with temperature even with the purge buttons. I suvgest a standard gauge. Almost all mechanical pumps ive used will bounce the needle. That is normal because of the cam activation.
Last liquid gauge i tried showed 6 psi on initial start and 3 psi at op temp, with a purge button. Aeromotive pump

Well, I was thinking it was just a gauge issue.  But if I put the old one back on it will just bounce around from 2 to 8 pounds, telling me nothing.  Maybe I have no problem, but it would sure be nice to know......

[c00nhunterjoe]

Idealy, you need to measure fuel pressure at wide open throttle under full load. Run a line out from under the hood and ziptie it to your wiper arm for testing. Wide open from a dig and look at the gauge at the top of 2nd gear and it will give you the numbers you need to know. At that rpm, the gauge willy be pretty steady.

[John_Kunkel]

Five psi is plenty as long as it will maintain that at WOT. It's about volume, not pressure.

[RECHRGD]

Five psi is plenty as long as it will maintain that at WOT. It's about volume, not pressure.

It's a 120 gph pump, so I'm guess I'm good.  Thanks guys!

[c00nhunterjoe]

I would still verify per my suggestion above.

[RECHRGD]

I would still verify per my suggestion above.

[BSB67]

It's a 120 gph pump, so I'm guess I'm good.  Thanks guys!

There is nothing in your above statement that implies or suggests that you are good.

The fuel pump rating has virtually nothing to do with the volume of fuel the pump will deliver under operating conditions.

If you have 3.5 psi at the carb, at WOT, at the top of a gear, and have a dual feed carb with 0.110" N&Ss, and less than 500 hp, you will be fine, from my experience.

[69wannabe]

I do not like liquid filled fuel pressure gauges. The reading varies greatly with temperature even with the purge buttons. I suvgest a standard gauge. Almost all mechanical pumps ive used will bounce the needle. That is normal because of the cam activation.
Last liquid gauge i tried showed 6 psi on initial start and 3 psi at op temp, with a purge button. Aeromotive pump

Same here, I put a liquid filled gauge on my fuel line and it wasn't accurate at all. I checked it with a standard gauge and it was 5 to 6 psi with my carter 6903 so I put the plug back in it and let it ride. I am running it on a 493 ci with a 850 holley double pumper with no problems.....