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Discussion Starter · #1 ·
The carb is a demon 625 with sight glass. The float levels are both adjusted correctly. New fuel pump and and clear plastic filter after the pump.

i Was driving today and the car just stalled. I checked the sight glass and the primary was really high.
normally the float level sits at about half sight glass or a little lower. Today it was sitting at 3/4 to almost to the top.
‘’it does this pretty regularly. i would Go back and adjust it back down or get it back to normal after messing with it for a while. Then after several days of driving it will flood out and the sit glass with be high. I haven’t checked the pressure yet. It usually runs about 4-7 on the liquid filled gauge at the carburetor.

im wondering if a rusty gas tank can cause this…..I’m sort of at a loss at this point
 

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It's a possibility that something is getting into the N&S, holding it open a bit then washing out. And that depends on what the filter is catching and what it's not. I usually look at those small filters as something for a lawn mower, not a performance engine or at most a secondary filter to the main one in front of the fuel pump. Are you setting the levels with the engine running? And is the fuel pump mechanical? I'm wondering about the 4-7 PSI, it should be a bit steadier than that but maybe with a mechanical pump there's more variation in the pressure.
 

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Discussion Starter · #4 ·
It's a possibility that something is getting into the N&S, holding it open a bit then washing out. And that depends on what the filter is catching and what it's not. I usually look at those small filters as something for a lawn mower, not a performance engine or at most a secondary filter to the main one in front of the fuel pump. Are you setting the levels with the engine running? And is the fuel pump mechanical? I'm wondering about the 4-7 PSI, it should be a bit steadier than that but maybe with a mechanical pump there's more variation in the pressure.
The fuel pump is stock mechanical. the levels are set with the engine running. I did start having this problem to a certain extent when I moved the filter after the pump. I was told that the filter was not supposed to be before the pump as the pump was supposed to be gravity fed. It seemed to have a starvation problem before I moved the line. But I didn’t look hard into why. I just moved it and figured it would correct that. The pre pump filter did seem to act as a regulator though
The gauge does bounce around some. I was going to put a regulator on it. It switches from 3-7 or so. I’d have to recheck.

As far as gauges go. I didn’t want the liquid filled necessarily. I got the one with the best review as they said the others had leaked gas all over the engine compartment at pressure and caught the car on fire.
and recommendations on which filter, where it should be located and which gauge I can safely run?
 

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Discussion Starter · #6 ·
The filter you’ve got should be fine And maybe your gauge too.
‘A lot of new mechanical pumps built these days seem to be way off on pressure maximum. I had one that was 9 psi.
I’ve used a fuel regulator like this to check pressures. Kinda cheap looking but good for test purposes.


Also going to add that it drained the secondaries to basically nothing. If that’s another clue.
While I don’t have the regulator. I can pinch off the line to regulate it.
 

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The fuel pump is stock mechanical. the levels are set with the engine running. I did start having this problem to a certain extent when I moved the filter after the pump. I was told that the filter was not supposed to be before the pump as the pump was supposed to be gravity fed. It seemed to have a starvation problem before I moved the line. But I didn’t look hard into why. I just moved it and figured it would correct that. The pre pump filter did seem to act as a regulator though
The gauge does bounce around some. I was going to put a regulator on it. It switches from 3-7 or so. I’d have to recheck.

As far as gauges go. I didn’t want the liquid filled necessarily. I got the one with the best review as they said the others had leaked gas all over the engine compartment at pressure and caught the car on fire.
and recommendations on which filter, where it should be located and which gauge I can safely run?
We've always put a filter in-between the tank and the pump. If the mechanical pump is working correctly it does not rely on any gravity assisted feed, the intake side of the pump will be the suction side and can easily pull fuel through a filter. There is nothing wrong with having a secondary filter between the output of the pump and the carb. A little extra insurance. If the secondaries are draining, then you need to find out what is going on there. The liquid filled gauges are something of a personal choice. Some guys believe it helps with dampening the gauge to get a more accurate reading and others like me tried them, didn't see any big plus and went back to dry gauges.
 

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Discussion Starter · #9 ·
Went out there today. Fired the car right up. bouncing between 5-7 psi consistently. Pinch the fuel line some and get an even 6 psi.
float levels perfectly even in the sight glass About halfway up. Idled smooth and ran fine.
a few grains of what looks like rust in the clear filter.
I’ll put another filter on there pre pump….

‘’but man……whats wrong with this thing. Maybe the float hung open.
the carb has been gone through pretty good. When this happened before is when I put the gauge on it and replaced the fuel pump…..the fuel pump was bad. i was going to put a regulator on it and still will just for good measure but I wanted it back on the road for summer driving as much as possible.
 

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With a mechanical engine driven pump you will see the pressure gauge bounce. The factory style pump is essentially a piston pump driven at cam speed. The piston in this case is a diaphragm but it operates with an up and down motion most similar to that of a piston in a bore. So it cycles from BDC to TDC and back thus the change in pressure between these extremes which is what the gauge is displaying. A regulator set at the lowest pressure you see on the gauge will damp the leak down quite a bit to deliver a more constant flow to the carburetor. With a pump of this type a dead head regulator is sufficient.

I generally filter ahead of these type pump‘s, it protects the valves in the pump from crud coming along with the fuel. A simple way to increase filtration area without adding a lot of resistance is to plumb two filters in parallel. That requires fabricating two sets of tee‘s and finding a suitable mounting location.

The increase in the sight window after a few days may be the plumbing between the pump and carb is holding pressure that slowly bleeds past the needle valve. As long as the adjusted level holds when the engine is running this is OK. This might also be from heat soak after shutdown. Modern fuels are blended for the needs of high pressure fuel injection not near atmospheric pressure of carburetors, an insulator spacer between carb and intake might provide some relief from this.

Bogie
 

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Get a paint can lid, for a catch can and place it under one of the bottom fuel bowl screws, remove the screw and check the quality of the gas that drains into the lid.
Fuel pressure can be lower if you have good flow, 1 quart in ten seconds with open line.
 
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