Newbie w/ low fuel pressure issue

[Henson80MGB]

I'm only a week into a 80 MGB and have a cutting out problem during driving after a bit.

I checked the fuel flow at the carburetor and it was weak.
Went to pull the fuel filter and determined that an aftermarket little pump replaced the original at some point. I removed the filter from the side of the aftermarket pump and tried to determine if it was plugged. It seemed very clear so we re-installed and checked the flow again, and it was then good.
Ran the car, and had the same cutting out issue, came back checked flow and it was weak again.
Replaced the fuel filter with a new one and checked flow, it was good. Ran the car had the same cutting out issue, checked flow and it was weak again.
Put the original filter back in, for grins, and had good flow, drove it a bit, and had the issue, and checked and it had weak flow again.

I'm now thinking something is in the gas tank that is clogging the filter until I blow it out, or is blocking the exit of tank.

Last week I added about 1/2 a tank of gas and have a bit less than that left in the tank now (it was pretty empty when I picked up the car).

So question is, does something in the tank seem the most likely? If so, what is the best way to clean out the tank? If not, what else should I look into?

Thanks, Larry

 

[Mickey Richaud]

Welcome to the party, Larry!

Have you tried running it a bit with the gas cap removed? You may have a blockage in the emission control system that's causing problems.

 

[Henson80MGB]

Thanks Mickey,

I just gave that a try, and unfortunately the car is still cutting out after a bit while driving even with the gas cap off.

So, I'm thinking of draining the gas tank in the morning and seeing what, if anything, comes out.

Larry

 

[Mickey Richaud]

Well, it was worth a try!

With all the horror stories about the havoc wreaked by ethanol, you may have some really yucky stuff in the gas tank. Hopefully, flushing it out will help. Carb rebuild may be in your future, as well. :frown:

 

[JPSmit]

I'm inclined to think tank too - don't forget there is 30+ years of residue in there.

 

[CZ_Dave]

The tank has a "PLUG" on the bottem
to drain the tank.
Drain the tank
You may pull the inline filter and line at the carburator,
then you can run a air hose to purge out
you fuel system, to clear any blockage.
You can pull the right rear wheel,
and remove the sending unit to inspect
the interior of the tank, then you
reinsert the sending unit (very easy to do when the tank is MT).
IF you determine that you stil do not have enough
pressure, then you may want to install a new fuel pump and use a inline pressure regulator.
Those are some of the things that have worked for me when
I restart a car that has been parked for a few years.
Just got one running that sat for 10 years, runs great.
Hope this helps and welcome to the BCF

 

[David_DuBois]

"The tank has a "PLUG" on the bottem to drain the tank."

I don't believe that the 80 MGB tanks have a drain plug, in which case the tank will have to be pumped 'dry' with a hose inserted through the filler tube.

The pickup tube is integral with the sending unit on a 80 MGB, so it would be a good idea to pull the sending unit/pickup tube out first to check for any obstruction in the pickup tube.

"IF you determine that you stil do not have enough pressure, then you may want to install a new fuel pump and use a inline pressure regulator."

"I removed the filter from the side of the aftermarket pump and tried to determine if it was plugged. It seemed very clear so we re-installed and checked the flow again, and it was then good."

The problem is not pressure related, it is reduced flow, most likely caused by an obstruction in the tank to pump line. It is best to stick with a pump that has the correct output pressure for MGBs (2.7 - 3.8psi) rather than getting a pump with higher pressure and installing a pressure regulator in line with it. The inexpensive pressure regulators tend to cause more problems than they resolve and a regulator with good performance is quite expensive.

It is very likely that there is something floating in the bottom of the tank that is being sucked over the pickup tube. The volume of fuel delivered by the OEM pump is 18 GPH or 2.4 PPM. A good way to check the flow is to direct the output line into a quart jar, marked at the one pint level, turn on the ignition and time how long is takes to pump 1 pint - should be less than 30 seconds.

For more fuel delivery troubleshooting tips, see the article, Fuel Delivery Troubleshooting Guide in the SU Fuel Pump Articles section of my web site at: https://homepages.donobi.net/sufuelpumps/
Cheers,

 

[Henson80MGB]

Thanks for the fantastic direction.

I drained the gas (siphoning was the way I had to go), it was a bit brown :frown:. Then found a youtube showing the removal of the outlet/sending unit and gave that a try.

Cleaned everything, put some more clean gas in the tank, pushed the bumper to move the gas around as much as possible and then siphoned that out also.

re-installed the sending unit. and put a bit of clean gas in the tank.

it started fine, ran for a while fine.

My wife was so happy she took it out for a spin and promptly ran out of gas

put more gas in limped to a gas station, put a new 5 gallons in the tank. (and figured out the sending unit / fuel gauge does in fact still work after I messed with it.)

And about ~40 miles of fun in the sun driving around and only a minor hiccup.

A few more tanks of clean gas, and I might be ready to claim victory.

Thanks again, Larry

 

[drooartz]

Woohoo!

 

[DrEntropy]

Onward thru th' fog!! :laugh:

And keep changing the filter, too. :wink:

 

[elrey]

:thumbsup:

 

[CZ_Dave]

Yeah Baby!