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Fuel pump, or something else?

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vagt6

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Hello, gents and ladies. Your advice on a fuel deliver problemo would be welcome.

My MKIII Midget runs fine around town on short trips. But when I go on the road at highway speeds, the engine dies after driving about 15-20 minutes sometimes. This has occurred three times over the last several hundred miles or so.

It sure seems like a fuel pump. After it dies, engine cranks but no fuel comes up through the line (with filter removed). Float bowls are clean.

Then, wait about 20 minutes or so and it will start and run for awhile. Maybe for 100 miles, maybe for 5 miles.

So, how might I test the fuel pump? Is there an effective way to determine if this will happen again. Should I just replace the fuel pump?

If it need replacing, what's a good one to use? Moss?

Any wisdom on removing/installing it?

Thanks, sorry for all the questions. :cryin:
 
Mark, next time this happens, remove the fuel tank filler/cap and see if you hear a sudden inrush of air. If the tank vent is plugged you might just be developing a vacuum in the tank.

BTW, is this a mechanical pump or electric pump?
 
Doug, many thanks.

It's an electric pump, starts clicking when I turn on the ignition. It's under the car. It did NOT pump for about 20 minutes, then mysteriously came back to life. Again, this only happens at highways speeds after about 20 minutes or so of driving. When it stalls, NO fuel is coming up through the fuel line at the carb filter.

I notice a rush of air when I open the cap to fill the tank with gas. I put a new cap (Moss) on it a while back. Would the vacuum make the pump stop?

Would opening the gas cap correct the problem, possibly?

How's the tank vented?
 
Ha, remove cap, replace with a peice of tin foil and use tape or rubber band to hold it on. Make a small hole in it with something like a tooth pick.


Test

The hole is what your present cap does not seem to have. Had same prob on a race car one time, had us seriously questioning our sanity.
 
Yes- it is conceivable that a vacuum COULD stop an SU pump from pumping, no harm in trying the "pinhole in the foil" test.
 
Bill, Jack, Doug, thanks. :driving:

Very strange, but worth a try. Only problem is, it only occurs when I'm about 15-20-30+++ miles from home. IF the tin foil thing doesn't work, it's the tow truck!

There is some vacuum there, when I remove the cap there is a "whoosh" of air like there's pressure being released.

Never happens around town or short trips. BTW, the car is in perfect tune, nice looking plugs, runs like a champ. However, the fuel starvation thing does seem to happen when the tank is near full. I don't usually keep much fuel in the car unless I'm going on a road trip. That's when it happens!

SO, the fuel system on this car requires a VENTED cap? The Moss replacement cap is NOT vented.

If I had enough hair to pull out, I might consider . . . :wall:

I'll keep you guys posted. Thanks so much for your astute suggestions!~ :thumbsup:
 
The pre-smog cars had vented caps the post-smog didn't but vented thru the charcoal canister up in the engine compartment. If the smog system has been modified then this vent has probably been plugged and now the vented cap is required (or the PROPER tube in question unplugged).
Bill
 
Mark, I like Jack's idea for a test. I'm sorry that it may require driving a distance that takes you away from home.

Is the electric pump an SU or other type? I know you've owned LBCs long enough that you have probably already tried "whacking the pump" with a chunk of wood when it stops pumping. SUs are prone to having their points wear after many miles and a good whack can temporarily bring them back to life.
 
you could also drive round the block 20 or 30 times... keeps you close to home, but It does seem like a vaccum prob.
 
Wow, I never considered this vacuum thing. You guys may have hit it, though.

It's a cheap gas cap, I'm gonna drill a very small hole in it and give it a go.

And of course, I'll be carrying the most valuable tool of all on my next road trip: my cell phone. :lol:

I'll let you know, it may take awhile to test this theory . . .

Again, many thanks to you all for the great input. :yesnod:
 
Billm said:
The pre-smog cars had vented caps the post-smog didn't but vented thru the charcoal canister up in the engine compartment. If the smog system has been modified then this vent has probably been plugged and now the vented cap is required (or the PROPER tube in question unplugged).
Bill
Click to expand...

There's a canister on this engine but it is not functional. The PO left it on, but it's not plugged into the system (or at least it doesn't look so).

Sometimes when I remove the gas cap, there is a bit of vacuum. Also, the fuel pump always comes back to life after one of these highway stalling spells. Works great at all other times.

Funny, how after all these years of playing around with LBCs (mostly Triumphs) I learn something completely new, never before encountered or considered.

I think it's voo-doo. :square:
 
Well, you diagnosed it yourself.... :thumbsup:

It is voo-doo... You went from a Triumph :banana: to MG's.... bad Kharma :nopity:
 
RonMacPherson said:
It is voo-doo... You went from a Triumph :banana: to MG's.... bad Kharma :nopity:
Click to expand...

actually around here we prefer to think of it as enlightened and wise :yesnod:
 
My name is Mark and I'm a car-aholic. I openly admit it. Point me at an antitque car and all logic is abandoned.

My first choice IS a Triumph, but I love MGs as well. Actually, I'd like a big Healey, but with the prices on them in the stratosphere (not on earth, but Mars), not likely.

I actually purchased this Midget on a whim to hold me over til I could find a nice TR-4. But this thing is so much fun I'm hardly thinking about a TR right now.

And please don't anyone try to sell me another LBC. No more room in the garage . . . :yesnod:
 
Congrats on buying a proper handling sports car. Welcome to the forum.
 
I bet you don't need the cell phone.
 
Unfortunately, when I aged past 17, my body height increased where I could no longer comfortably fit in any MG product.... Triumphs, ok, some a little tight, especially spitfires... But seems like even they offer more legroom thatn midgets...
 
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