Jay
Fuel related problems can be a bear to figure out.
I read an article a number of years ago that stated " when you think
you have a carb stumble problem the 1st thing to check is your distributor
timing and advance curve". I worked on a K code Mustang that had a terrible
idle and stumble. The distributor advance was the problem. Fixed the
distributor and the problem was gone.
This was an early style distributor with the oil port. They have
wear points in the advance mechanism and those wear points caused the
problem. The later style distributor does not have those wear points but
the advance mechanism can get gummed up and don't move correctly. I would
also check all the wires to the distributor to make sure you have good
connections and good wires.
The Shop manual lists the stock SU fuel pump @ 15 GPH and around 2
psi. I believe almost every electric fuel pump on the market today has
almost double that GPH with pressure from 2 to 7 psi.
Any carb should work OK with up to 5 psi pressure. You don't want
to exceed the pressure that the float can shut off the fuel flow or the carb
will flood.
The Holley has a nylon cam for the accelerator pump - it maybe worn
or loose. I believe there are some adjustments for the accelerator arm. I
would check to make sure your getting a good steady squirt of fuel when you
move the throttle.
You should check the fuel bowl level - make sure it is correct.
If nothing here works - tear the fuel system down - check and clean the fuel
bowls and carb - clear all fuel lines - replace fuel filter
You could check the fuel flow of the pump by re-directing the fuel to a jug
of your choosing and run the pump for a short given time - measure the
amount of fuel - calculate GHP
Hope this helps
Ron Fraser
-----Original Message-----
From: Tigers [mailto:tigers-bounces@autox.team.net] On Behalf Of Jay Laifman
Sent: Friday, May 30, 2014 3:42 PM
To: tigers@autox.team.net Den
Subject: [Tigers] Fuel Pump Question
I rebuilt the stock pump and it was working fine. It failed. I grabbed a
new Carter vane type pump I happened to have from another car and threw it
in. It worked for a short while then failed. Then I grabbed one last Facet
pump I happened to have. It is working, and still working. But the car is
now not running perfectly. I don't know if it is related to the fuel pump.
But I've only noticed it since I change fuel pumps - and changed the spark
plugs and wires.
I put a fuel pressure gauge on and found that this pump is putting out 4.25
psi. I've looked around and have seen that 5.5-6 psi is suggested - but I
can't confirm if that is correct for a 260 with a Holley.
The problem I'm having is that I'm getting a little stumble on initial
acceleration and I've noticed when I take my foot off the gas, like to shift
up, the rpm drops all the way to 0, but does catch up again.
One thought was that this fuel pump doesn't have enough volume for the
carb/engine - or different enough volume that the float bowl is not at the
same level as it was with the old pump. But I don't know if that make
sense.
Another thought was that the accelerator pump is not putting out enough
fuel. But, I haven't changed the accelerator pump and that wouldn't explain
the far drop to 0 when lifting off the gas. Although I don't know for sure
if the two are related.
Thanks for any thoughts. _______________________________________________
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