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Discussion Starter #1
I now know that I have a 750 Holley Double Pumper carb on this car. It has a Mallory Electric Fuel pump and regulator. When I first got the car it ran about 8 psi on the gauge by the carb. I drove it up to a local shop to get the coolant flushed and filled and as we were running it the fuel pressure kept dropping. By the time I got it home it was about 2 1/2 to 3 psi. I had the alternator and batt tested while I was there - the batt was low on cranking amps and the alternator was not functioning properly. The car was still running and it started a little slow but it started. Is my fuel pressure problem due to low electricity or do I have another problem? The tank was brand new when the car was built so there shouldn't be any rust or junk coming from it. I'm going to take the alt off and have it tested again later this week.
 

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Discussion Starter #3 (Edited)
I'm at work now so I can't go look - but I think it is a liquid filled gauge. I do know the glass face has a crack in it.....
It just seems really wierd that it would have 8 psi all the time until today and it just started losing pressure. The pump was still making it's normal noise also - just the gauge reading was scaring me. I don't want to have it quit on me or lean out the motor too bad. It's hard to tell if it was actually cutting out on me because it lopes so much.

While I'm on the subject - It has the electric pump and a MSD ignition box. I think the alternator is a 42 amp. Is the alternator big enough to run this stuff?
 

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I have a cheap liquid filled guage on my car. When its cold it shows 6 PSI; when the engine is warm the guage reads 0 PSI. I checked my presuure it with two other guages; it was still at 6 PSI. I know now the guage was worth much less than I gave for it.
 

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Nova_Guy said:
I have a cheap liquid filled guage on my car. When its cold it shows 6 PSI; when the engine is warm the guage reads 0 PSI. I checked my presuure it with two other guages; it was still at 6 PSI. I know now the guage was worth much less than I gave for it.
Yup, the liquid filled gauges can do that (mine did).
 

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My "at least" 21 year old Auto Meter guage reads the same as pressure test guage that I used. I guess you do get what you pay for.
 

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Discussion Starter #7
So, you guys think I have a gauge problem instead of a "real" problem? I hope so. I'll see if I can get another gauge in the next day or two. I had another guy suggest that maybe the tank isn't vented and the pump is sucking a vacuum on it. I'll try removing the gas cap and see if that is it also.
 

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Discussion Starter #9
I had it on a battery charger for about an hour yesterday when I got it home, and again for about an hour today. I started it up and it was reading about 8 psi again. So I have it narrowed to 3 things - bad gauge, bad alternator or battery or both, and the "unvented tank" idea. I'll have some time to mess with it tomorrow.....

Also - How do you change the pressure at the regulator? It looks like there is a jam nut and allen bolt in the top of the regulator. I would assume you would loosen the nut and screw in or out the bolt and adjust by the gauge??? There is an allen bolt in the side of it also. (Mallory Regulator)
 

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but I think it is a liquid filled gauge. I do know the glass face has a crack in it.....
Would the crack on the gauge have any effect on how its reading? Just a thought.
 

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Discussion Starter #11
Update: the gauge is not a liquid filled gauge. It is a "Jegs" gauge and it does have a crack in the face. Found out today the alternator is bad so I'm replacing that tomorrow. I took the gas cap off today after the pressure dropped on the gauge and there was no change in the gauge reading, so it's not a vacuum issue. I'll know after I change the alt tomorrow if it is still dropping. I guess the only thing left would be the " bad gauge when warmed up" idea.....
 

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Discussion Starter #12
Update: I replaced the alternator with a 61 amp one - seems to have cured the battery problem. I drove the car to two "cruise ins" this weekend, about 25 miles each trip, and the fuel pressure gauge drops to about 2.5psi or less once it warms up. Took gas cap off - no difference. I need to get my carb and timing set up right - but the car still seems to be "cutting out" a little cruising at 40-50 mph at about 2500 rpms.
Runs pretty good when you gas on it though......
 
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