TRExp

Spitfire & GT6 Forum

bubbles from bottom of fuel pump

Moss Motors
AutoShrine Sponsor
AutoShrine Sponsor
AutoShrine Sponsor
AutoShrine Sponsor

Limey Midget Man Avatar
Limey Midget Man John McGuire
Raytown (Kansas City), Missouri, USA   USA
1975 MG Midget 1500 "Liberty"
1979 Triumph Spitfire 1500 "Justice"
1979 Triumph Spitfire 1500 "Justice"
I just installed a freshly rebuilt 1500 engine with 0.020" over pistons & rings, a new cam, and the "Made in Spain" Weber carb I have been using for a year. I am using the old mechanical fuel pump that came on the car when I bought it 3 years ago. It appears to be a Weber, but not sure. I installed a Holley fuel pressure regulator, and the car has always been happiest running at about 1.0 to 1.5 psi fuel pressure (per the new gage I installed after wondering if the old gage was faulty). The new engine idles smoothly, (not broken in yet) but twice now, the very first 2 times I tried to take it out for a drive, it cuts out as soon as I give it enough gas to let the clutch out on a slight incline from a stop sign. Maybe the miniscule fuel demand at idle doesn't challenge the fuel supply like it does when trying to climb a slight incline. As soon as it sputters, it wants to die on level ground too. Back in the driveway I noticed that bubbles are coming up from the bottom of the fuel filter, as if the suction is pulling in air from a loose clamp, but it is snug. Then I noticed the fuel pressure regulator was suddenly reading zero, and the engine sputtered severely and died. No amount of adjusting the fuel pressure regulator got it to read any pressure. I'm wondering if the old fuel pump finally gave out. Both fuel filters have been changed twice when fuel tank crap finally showed up in the filters. Any idea why bubbles would get sucked into a fuel filter, and the pressure reg all of a sudden go to zero psi? An electric fuel pump might be in my future. Thanks.

. Hide banner ads & support this website by becoming a > Gold Supporting Member <
colodad Avatar
colodad Silver Member Calvin Williams
Grand Junction, Colorado, USA   USA
1979 Triumph Spitfire 1500 "Spitty"
John,
just a thought here.
If the fuel line is cracked but not completely broken away at the tanks top, the pump could suck air into the system, and when the engine is off air could let fuel drain back into the tank.
Take a look there, move the line, see if a connection is loose, it could show a wet spot at that area.

Yellowhawk Valley Avatar
walla walla, washington, USA   USA
1969 Triumph Spitfire "Walla Walla"
1969 Triumph Spitfire "Portland"
1972 Triumph Spitfire MkIV "Spokane"
1975 Triumph Spitfire 1500 "Dayton"    & more
You could also be getting air past a damaged diaphragm in the mechanical pump. Also creating a 0 pressure.
Dan

. Hide banner ads & support this website by becoming a > Gold Supporting Member <
Limey Midget Man Avatar
Limey Midget Man John McGuire
Raytown (Kansas City), Missouri, USA   USA
1975 MG Midget 1500 "Liberty"
1979 Triumph Spitfire 1500 "Justice"
1979 Triumph Spitfire 1500 "Justice"
In reply to # 1474274 by colodad John,
just a thought here.
If the fuel line is cracked but not completely broken away at the tanks top, the pump could suck air into the system, and when the engine is off air could let fuel drain back into the tank.
Take a look there, move the line, see if a connection is loose, it could show a wet spot at that area.

I will look at that. Thanks.

Limey Midget Man Avatar
Limey Midget Man John McGuire
Raytown (Kansas City), Missouri, USA   USA
1975 MG Midget 1500 "Liberty"
1979 Triumph Spitfire 1500 "Justice"
1979 Triumph Spitfire 1500 "Justice"
In reply to # 1474296 by Yellowhawk Valley You could also be getting air past a damaged diaphragm in the mechanical pump. Also creating a 0 pressure.
Dan

As much as I would enjoy opening up the mechanical pump and replacing the diaphragm (just because I enjoy fixing things), now might be the time to invest in a low pressure electric fuel pump. The mechanical pumps put out too much pressure for the Weber carb anyway. Also, there's a small chance that the fuel bubbling issue after engine shut-off might go away or diminish. Thanks.

Limey Midget Man Avatar
Limey Midget Man John McGuire
Raytown (Kansas City), Missouri, USA   USA
1975 MG Midget 1500 "Liberty"
1979 Triumph Spitfire 1500 "Justice"
1979 Triumph Spitfire 1500 "Justice"
In reply to # 1474296 by Yellowhawk Valley You could also be getting air past a damaged diaphragm in the mechanical pump. Also creating a 0 pressure.
Dan
I think you nailed it, Dan. I noticed fuel sitting on top of the fuel pump, which had leaked past a defective diaphragm and out the capscrew holes on top. I am trying to find new neoprene sheet mat'l to make a new diaphragm out of. In the mean time, I invested in an electric fuel pump and installed it. I have the regulator set to run at 1.0 psi, but after 2 -3 minutes idling (very smoothly) it drops to zero psi and stalls after a minute or so. It's like it fills the float bowl but then can't pump any more. I can hear it pumping, so I have to wonder if there's a blockage in the line along the frame rail. The fuel filter directly out of the tank is new. I will check to see if it is clogged. Thanks.

colodad Avatar
colodad Silver Member Calvin Williams
Grand Junction, Colorado, USA   USA
1979 Triumph Spitfire 1500 "Spitty"
I once had a fuel line separate inside, a flap formed inside closed the line like a check valve. I found it when I removed the line, could see the break.

. Hide banner ads & support this website by becoming a > Gold Supporting Member <
spitfire50 Avatar
spitfire50 Paul Mugford
Rochester, N.H., USA   USA
In reply to # 1477588 by Limey Midget Man
In reply to # 1474296 by Yellowhawk Valley You could also be getting air past a damaged diaphragm in the mechanical pump. Also creating a 0 pressure.
Dan
I think you nailed it, Dan. I noticed fuel sitting on top of the fuel pump, which had leaked past a defective diaphragm and out the capscrew holes on top. I am trying to find new neoprene sheet mat'l to make a new diaphragm out of. In the mean time, I invested in an electric fuel pump and installed it. I have the regulator set to run at 1.0 psi, but after 2 -3 minutes idling (very smoothly) it drops to zero psi and stalls after a minute or so. It's like it fills the float bowl but then can't pump any more. I can hear it pumping, so I have to wonder if there's a blockage in the line along the frame rail. The fuel filter directly out of the tank is new. I will check to see if it is clogged. Thanks.
John,
That doesn't sound like a bad pump diaphragm to me. The fuel should all be on top of the diaphragm. It is when the fuel gets through the diaphragm and makes its way into the oil pan that you have trouble. Leakage out the top screw that holds the cover on the pump is just a matter of replacing the leather seal on the screw. Leakage around the rim of the pump is more serious, but a good fuel proof sealant applied to the edges of the diaphragm should stop leaks there.
All the best,
Paul

Limey Midget Man Avatar
Limey Midget Man John McGuire
Raytown (Kansas City), Missouri, USA   USA
1975 MG Midget 1500 "Liberty"
1979 Triumph Spitfire 1500 "Justice"
1979 Triumph Spitfire 1500 "Justice"
Replacing the neoprene fuel line from the tank forward, and both filters seems to have stopped the air bubbles in the fuel filter. The old mechanical pump and the new electric pump BOTH had the same problem with fuel pressure dropping to zero a few minutes after starting the car. I would turn the key to let the pump prime the line again, and watch the gage climb to the 1.0 psi point. Started the car, ran perfect for a few minutes, then pressure down to zero again. SO, the big news is that I went out on a limb to try one last thing.... Just as the gage started dropping to zero, I popped open the fuel filler cap, and the gage went right back up to 1.0 psi. I'm trying to figure how to let air return to the tank without causing a vacuum leak to the carb.

. Hide banner ads & support this website by becoming a > Gold Supporting Member <
Yellowhawk Valley Avatar
walla walla, washington, USA   USA
1969 Triumph Spitfire "Walla Walla"
1969 Triumph Spitfire "Portland"
1972 Triumph Spitfire MkIV "Spokane"
1975 Triumph Spitfire 1500 "Dayton"    & more
Wow, I run a 79 and had vacuum lock issues at one time as well but never that fast even with a full tank. My guess is the vent line starting right at the fuel separator on top of the tank is full of fuel instead of air. When mine occurred it was due to the vent line past the separator actually having gas in it. That part is simple, just disconnect up front, pop the tank lid and let it run. I also put an air hose to it to make sure it was clear.
Is your tank filled above the nozzle stop so you have no air space at all?
Dan

Doug in Vegas Avatar
Doug in Vegas Douglas D
Las Vegas, Nevada, USA   USA
In reply to # 1477779 by Limey Midget Man I'm trying to figure how to let air return to the tank without causing a vacuum leak to the carb.

Pull the panel in the trunk.

Look way up on top of the tank for a rubber hose leading to a line that runs to the front of the car. There should be an inline brass coupling that has a tiny hole in it so the tank can breathe.

Limey Midget Man Avatar
Limey Midget Man John McGuire
Raytown (Kansas City), Missouri, USA   USA
1975 MG Midget 1500 "Liberty"
1979 Triumph Spitfire 1500 "Justice"
1979 Triumph Spitfire 1500 "Justice"
When I changed both fuel filters today, the new electric fuel pump was not self-priming so I gently nudged fuel forward from the tank by squirting tiny bursts of compressed air into the return line at the carbon cannister. I might have the return system altered by accident. I will take a photo of the way my vac lines connect at the carbon cannister, and the way I have some rubber caps on the cannister ports. When I first installed the engine and started it, I could hear a hiss from the carbon cannister, and the idle was rough. Immediately upon capping a top port, the idle smoothed out. Not sure if this inadvertently caused the return line to stop allowing air back to the tank.

Doug in Vegas Avatar
Doug in Vegas Douglas D
Las Vegas, Nevada, USA   USA
More likely when you blew air into the breather hose you blew debris into the orifice thus clogging it.

Limey Midget Man Avatar
Limey Midget Man John McGuire
Raytown (Kansas City), Missouri, USA   USA
1975 MG Midget 1500 "Liberty"
1979 Triumph Spitfire 1500 "Justice"
1979 Triumph Spitfire 1500 "Justice"
Thanks Doug. That's kind of why I included that info... in case someone could tell me what it might have caused. I will be removing the return line and orifice tomorrow.

Limey Midget Man Avatar
Limey Midget Man John McGuire
Raytown (Kansas City), Missouri, USA   USA
1975 MG Midget 1500 "Liberty"
1979 Triumph Spitfire 1500 "Justice"
1979 Triumph Spitfire 1500 "Justice"
Two photos show the threaded (90 degree) vacuum fitting that I threaded into the Weber intake manifold, and the top & bottom ports of the carbon canister that I have placed aluminum tape over. Strangely, at first when I punched a mere pin-prick sized hole in the aluminum tape (as an experiment to see if it allowed the return air to get back to the gas tank), the engine immediately idled roughly, but in less than a minute it smoothed out. The fuel pressure regulator still slowly dropped in pressure, indicating that there still wasn't enough return air getting into the tank so I popped oped the gas filler cap. Almost immediately the fuel pressure regulator gage jumped back to where I had set it at 1.0 psi. I will be investigating further tomorrow, since the (fuel/air separator??) is evidently clogged.


Attachments:
Vac and return lines.1.jpg    28.6 KB
Vac and return lines.1.jpg

Vac and return lines.2.jpg    44.5 KB
Sign In or Register to view this photo
. Hide banner ads & support this website by becoming a > Gold Supporting Member <

To add your reply, or post your own questions

Members Sign In   or   Create an Account

Registration is FREE and takes less than a minute!


Having trouble posting or changing forum settings?
Read the Forum Help (FAQ) or contact the webmaster