Fuel Pump Pulsing/Pressure Question

Post by **ARCHINSTL** » Fri Nov 18, 2005 6:44 pm

I installed a new fuel pump from Advance a while back - the stock $25 Master Model 1347.
I am still searching for elimination of hesitation/rpm cycling; should one be able to feel a "pulsing" on the rubber fuel line from the rigid pipe to the pump? This is the hose between the steel pipe on the firewall and the inlet pipe atop the "dome" at the back of the pump. I do not have a way of testing the actual pressure.
It kinda feels like there are pulses (air bubbles?) when the hose is squeezed. A friend told me this is normal, but at this point I am ready to believe advice from a sorcerer or wizard or necromancer to solve these problems - any of you guys out there?
Thanks,
Tom M.

Typrus · Post by **Typrus** » Fri Nov 18, 2005 11:52 pm

How fast is it pulsing? Our pumps are lobe-driven off the cam and use a diaphragm, so they do pulse inherantly, but to what degree and what frequency.

Post by **ARCHINSTL** » Sat Nov 19, 2005 1:13 am

Sorry - I neglected to quantify.
At idle, one can feel a pulse (or "bubble"?) several times a second. At a little more than an idle, the pulses are still there, but closer together. They feel exactly like, well, "bubbles" in the line.
Now, I have asked before about noticing air bubbles in the top of the fuel filter. This has occurred with two new filters. I thought something was amiss, but both the AZ and Advance "experts" advised that this was normal (and indeed, a "real" mechanic concurred with them). On a member's advice, I replaced the three rubber hoses at the tank, which was a real PITA, and also blew out all three of the steel lines with compressed air and captured what came out, which was - nothing - just a little liquid fuel. I checked the filter with the filler cap off and the flap propped open, but the bubbles are still present. It would seem that the bubbles are related to the feeling of bubbles in the hose to the pump; but whether that makes a difference in what the pump actually feeds the carb, I do not know.
I do understand your explanation of the pump's operation, but I had never considered/noticed this pulsing before - so enquired. Believe me, I am really grasping at anything which can help.
I guess I need to know if anyone else can feel a pulsing in that hose as well; if so, at least I can forget about the bubbles...
Thanks,
Tom M.

takza · Post by **takza** » Sat Nov 19, 2005 3:57 am

The liquid gas is more or less non-compressible...and the pump diaphram pushes it out in cycles since it is operated off of the cam...so the pulses are from the rubber line expanding from the pressure on the gas.

The hesitiation might be more vacuum related? Maybe in the carb?

Post by **ARCHINSTL** » Sat Nov 19, 2005 12:30 pm

takza -
Thanks - I feel better now about the pulsing.

My adventure today is to (recheck) the Deceleration Fuel Cut System and the Vac Switch "A", as on again perusing the wonderful FSM, it seems the only thing/system whose operation starts/stops at the RPM range I am experiencing the cycling is this one - mine is 2200 to 1800, and this system is supposed to cut in and out at 2290 and then to 1900. Maybe this system is awry and causing the cycling when it's not supposed to. I'm really grasping...

The carb is a new FC unit and all vac lines are new.

Tom M.

Typrus · Post by **Typrus** » Sat Nov 19, 2005 1:30 pm

Make sure you didn't forget to connect anything and that everything is fully connected.