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This is getting ridiculous

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Dadandson

Dadandson

Jedi Trainee
Offline
Is it possible for the electric fuel pump to loose it's prime?
 
Not really but if there is a hole in the hose before the pump or at the fitting, it will suck air.
also if you vented gas cap has rusted closed, it will be trying to suck against a vacuum.
For a quick check of your cap, remove it and listen for a rush of air.
 
Maybe I need to provide more information. I have a 74 Midget 1275 motor with the smog stuff. I replaced the valve cover with a non vented cover so I thought that since the line from the cover to the smog "bottle" was not attached that maybe the tank needed the vacuum to work properly. Then I noticed I was almost out out of fuel. I replaced the valve cover with the original, re attached the vent line and put 4 gallons of fuel in the tank. I hear the pump running and if I put my finger over the fuel line at the carbs I can hear the pitch change on the pump but still no fuel at the carbs. That is why it seems to have lost it's prime. Prior to my changing the valve cover it was working fine. I will send the alloy cover to anyone who can help.
 
I don't need the alloy cover, but a tiny piece of dirt in the pump's valves can cause it to partially or completely fail. You could pressurize the tank slightly which would get it primed & possibly dislodge any dirt in the valves. As a check, if you blow on the carb end of the line, there should be no air returning to the tank.
D
 
Can I use compressed air from the line at the carb or do I need to remove the pump and visually examine?
 
You shouldn't be able to blow from carb side thru the pump. The check valves are set up to go only the other way. Dave's suggestion of blowing thru it was as a test of those check valves only. Try ~mildly~ pressurizing (no more than 10 PSI!) the tank with the line at the carb disconnected and directed into a bottle. You may have an internally collapsed piece of rubber fuel line. Ethanol blended fuels can do that to some lines.
 
It is a SU pump. Can I dissassemble the pump to find debris? I don't want to make things worse.
 
Yes, but on a bench. And arm yourself with some info. A Bentley manual for the car will have the relevant info, Haynes as well though not as good.

If the thing is running (ticking) it can pass a fairly large piece of debris without problems... I would be looking to lines and filter for possible problems THERE before I'd be goin' after the pump. They're pretty rock-proof.
 
I disconected the line before the in-line filter at the carbs, nothing. It is ticking like it always has. Can I disconncet the line from the pump to the tank and use compressed air to try to clear and then from the pump to the carbs to clear or will I cause some other problem?
 
I really don't want to cause more damage. I have to take the car in for a clutch and throwout bearing. Or maybe I should leave it up to Glenn at the MG Shop?
 
Un do all the lines. Front to pump and from pump to tank. Blow em out or suck on them and see where the problem is.
 
I have successfully got a bad fuel pump to "prime" by blowing into the gas tank. Yes crudely by just sticking my mouth on the filler and blowing, it will pressurize.
 
Stuff a rag into the filler and pressurise with an air nozzle. It won't seal well enough to hurt the tank but it will prime if there isn't any blockage. Did this a coupla times on ground power equipment with GMC diesels when they were run dry. The lift pump on a DD won't pull a prime unless you are lucky, I wasn't.
 
I blew out both line to and from the fuel pump with no luck. I will replace the pump. Thanks anyway everyone.
 
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