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  #1   IP: 63.239.69.1
Old 08-30-2007, 12:21 PM
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How much fuel should a fuel pump pump if a fuel pump does pump fuel?

What a PO of my 1975 Newport 28 did to the electrical system (which I've finally worked out), he also did to the fuel system. Rather than the basic "tank to a filter to the pump to the carburetor", he had the line from the tank going to a pump, then to a glass, non-Coast-guard-approved inline filter, to the original fuel pump, then to the carburetor. He had also disconnected the original fuel pump's power supply from the oil pressure switch and made it a permanent manual switch on the dashboard. To start the engine one pulled the choke, turned on both pumps, then started the engine, remembering (hopefully) to turn them off when the engine stopped.

Since my engine has recently decided to basically not run any more (starts OK but won't go above an idle and that only with the choke full out), I figured I'd reconfigure the fuel system back to the original design and start from there. I don't have a Racor filter yet, so I replaced the glass filter with a regular steel-body filter, and put a primer bulb in place of the first pump, since I'll need that later for the Racor anyway.

So now my system is tank to primer bulb to inline filter to pump to carburetor. I checked the flow through each piece of line to make sure that there were no blockages, and everything was fine. Finally, I pulled the line from the pump off the carburetor and put it into a jar, then started the fuel pump to see how the original equipment was working.

Thus my question: when I turned the pump on, the fuel came out (and looked and smelled OK to me) in a nice pulsed stream that would have filled a pint in about 30 seconds or less, I'd guess (I only let it run long enough to verify it was working).

Does that seem like the correct flow rate for that pump? The fuel didn't come out like from a garden hose, but at a good clip that certainly seemed like enough to run the engine.

Unfortunately, when I tested the arrangement the engine started up nice and I was encouraged, but then I saw I'd forgotten to turn the pump on and the fuel burned out of the carburetor before I could get to the switch. Afterwards I couldn't get it to run as well, but I didn't have any more time to reprime the line so I left it for next time.

I apologize for the long story, but basically all I need to know is "Does that flow rate sound about right for that pump?"

Thanks!
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  #2   IP: 206.230.48.34
Old 08-30-2007, 02:04 PM
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It seems right. The A4 burns about a gallon or a gallon-and-a-half an HOUR, so 2 pints a minute should be fine. (It's 8 pints to a gallon).
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  #3   IP: 63.239.69.1
Old 08-30-2007, 02:48 PM
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Thanks. It's looking more and more like a gunked-up carb, though I haven't checked the points yet. Replacing the plugs last week did help some, but obviously there are serious fuel starvation issues here to be resolved.

One thing that made me happy is when I removed each plug I used a mirror and light to look inside. All I saw in each case was the burned top of a cylinder head; no oil, no water, just plain old cylinder head. I haven't yet checked the compression, as I didn't have a tester when I did the plugs. I'll do that with the points.

Thank goodness I grew up working on my own cars back in the '70s; this is like old times!
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  #4   IP: 206.230.48.34
Old 08-30-2007, 05:26 PM
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> I haven't yet checked the compression, as I didn't have a tester
> when I did the plugs. I'll do that with the points.

Using the points to test compression is likely to give inconclusive results and could damage the points.
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  #5   IP: 76.106.7.221
Old 08-30-2007, 09:39 PM
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Sorry, I was unclear as to my meaning. What I meant to say is that I'll check the compression and the points at my next visit. I don't even know a way to use the point to test the compression.
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  #6   IP: 167.80.246.204
Old 12-02-2009, 01:03 PM
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just did mine too

just did mine too... points/plugs/condenser/coil... then 8 hours with a qtip and the carb.... the carb was my guilty party, and now she is running. when reassembling the carb, i had to make sure to use the new clip for the pin under the float to ensure proper mobility otherwise the operation wasnt too bad... i did mine in sections so i wouldnt get too confused.

to test compression i just put my finger in a spark plug hole... for a rough approximation anyhow.... also, when i got the carb done, let some marvel soak in the cyl.s, left sparkplugs out, put a towel over the engine, turned it over and made sure the towel was moving from the compression escaping the holes... again...not very scientific

Last edited by QuickMick; 12-02-2009 at 01:05 PM. Reason: more info
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  #7   IP: 71.252.4.191
Old 12-02-2009, 09:22 PM
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Quinn, sounds like a reasonable test. Good trick with the towel to observe each cylinder.

An inexpensive compression gauge is about $30 at the local auto parts store..I bought one to test the compression on a rebuilt Honda engine I did a few years ago, and have found it MUCH more useful for the A-4. Repeated MMO treatments (squirt, turn over, let sit, come back tomorrow/next week & restart) has resulted in a start from a suspected stuck valve and a range of ~40 to 80 PSI across the cylinders, to all four cylinders between 85-95 & no more stuck valve...the compression gauge instantly told me!

money well spent!
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Last edited by sastanley; 12-02-2009 at 09:24 PM.
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