Buick35 Posted November 9, 2023 Share Posted November 9, 2023 Could a regular brass or steel fuel shut off valve be used to regulate fuel pressure? Seems it would be cheaper than a regular one. Just curious.Thanks Link to comment Share on other sites More sharing options...
dl456 Posted November 9, 2023 Share Posted November 9, 2023 A shut-off valve will regulate volume and may increase pressure. Sometimes fuel pressure regulators will also reduce volume. Dennis Link to comment Share on other sites More sharing options...
keiser31 Posted November 9, 2023 Share Posted November 9, 2023 I use a small, pancake style regulator. Link to comment Share on other sites More sharing options...
DFeeney Posted November 9, 2023 Share Posted November 9, 2023 I would say the shut off valve regulates flow not pressure. They are different. The small regulators that John referred to cost in the $40, range. Buy one , install it, set the pressure, Bam your done. 1 Link to comment Share on other sites More sharing options...
Bloo Posted November 9, 2023 Share Posted November 9, 2023 (edited) 6 hours ago, Buick35 said: Could a regular brass or steel fuel shut off valve be used to regulate fuel pressure? Seems it would be cheaper than a regular one. Just curious.Thanks In theory, yes, in a car with a return line. It has been done on at least one fuel injection system that is not very sensitive to fuel pressure, anything between about 12 and 18 PSI would have run OK. They used a simple restrictor orifice in the return line. The size of the orifice set the pressure. I doubt this approach is ever practical on a carburetor. It won't work even in theory on a car with only one line for the fuel. When the carburetor bowl is full and the float valve closes or tries to close, there is no demand at all. With the fuel line dead-headed like that, the fuel pressure would just rise to the maximum available pressure instantly. It would blow the float valve open and run the carburetor over. A restriction in the line would also mean there is not enough flow available to pull hills. The amount of fuel an engine uses constantly changes due to load. That is why regulation is needed when the supply pressure is too high. In the old days with mechanical fuel pumps, the spring pressure on the fuel pump diaphragm set the fuel pressure. That was was relatively easy for the engineer designing it to calculate. Easy as long as he knew how many pounds force the spring provided, and how much surface area there was on the fuel pump diaphragm. With plain gravity feed or a vacuum tank, the distance of vertical drop and the weight of the fuel determine the pressure. That is also predictable and fairly easy to calculate. You can't fool mother nature. Good regulators that actually work are expensive, and might need a return line added. Edited November 9, 2023 by Bloo (see edit history) 4 Link to comment Share on other sites More sharing options...
Buick35 Posted November 9, 2023 Author Share Posted November 9, 2023 1 hour ago, DFeeney said: I would say the shut off valve regulates flow not pressure. They are different. The small regulators that John referred to cost in the $40, range. Buy one , install it, set the pressure, Bam your done. I tried one like that and hooked up a fuel pressure gauge to it and couldn't to go lower than 3.5 or so,everyone on a v.w. forum said that my kadrone carbs. shouldnt get more than 2.5. It's not running bad though without one. Maby I should just go with it or try another regulator. Link to comment Share on other sites More sharing options...
Hemi Joel Posted November 9, 2023 Share Posted November 9, 2023 (edited) A regulator maintains the same pressure regardless of flow. A partially closed valve does not. Say for example you have an electric fuel pump in the back of the car by the tank and it generates a pressure of 7 PSI. But your old carburetor will only tolerate 3 PSI without pushing fuel past the needle and seat and flooding the carburetor. If you close down the valve so that you have 3 PSI at idle, it will be almost completely closed. When you apply throttle and the carburetor needs more fuel, not enough fuel can get through that tiny opening at the valve and the carburetor will starve, stalling the motor. If you open the valve enough to provide sufficient fuel at full throttle, then the large opening at the valve will not squelch the pressure enough at idle to prevent the car from flooding. A regulator has a built-in valve that is controlled by a diaphragm that is sensitive to fuel pressure on the outlet side. So when pressure on the outlet side begins to drop, it opens the valve more. And vice versa. I like this one because it's easy to adjust with no tools, it has a dial that is marked in PSI for adjusting it, it is reliable, and is on the low end of the cost scale. https://www.summitracing.com/parts/mrg-9710 Edited November 9, 2023 by Hemi Joel (see edit history) 2 Link to comment Share on other sites More sharing options...
dl456 Posted November 10, 2023 Share Posted November 10, 2023 Not a fan of pressure regulators. In the case of the VW, volume may not be an issue, but the cheaper regulators set to a setting of less than 5 lbs. will limit volume at high end. This can create other running issues. If you need one, buy quality. Dennis 1 Link to comment Share on other sites More sharing options...
Mark Shaw Posted November 10, 2023 Share Posted November 10, 2023 Bloo wrote an excellent explanation above. I have used the cheap fuel regulators for years with no issues. They might not work well for 40s - 60s cars with larger engines, but they have worked well for me with teens and 20s cars that have much lower demand for fuel. 2 Link to comment Share on other sites More sharing options...
dl456 Posted November 10, 2023 Share Posted November 10, 2023 Hello Mark, I am glad you had good success with the regulators. The last regulator that I threw out was on a 1920 Studebaker, 289 cu in., single barrel Stromberg. On heavy load, this car would always lean out. A problem we chased for a while. We had the regulator set to approx. 2 lbs. to accommodate the needle in the Stromberg. This is still twice the head of the original vacuum tank. Long story short, switched to vacuum tank twenty years ago and never ran better. My only point was not to create a problem while fixing one. Dennis Link to comment Share on other sites More sharing options...
nat Posted November 10, 2023 Share Posted November 10, 2023 OEM equipment will deliver fuel at the correct pressure. If for some reason that can't be used, use a fuel pump that is regulated to a pressure that the carburetor can handle. Link to comment Share on other sites More sharing options...
zepher Posted November 10, 2023 Share Posted November 10, 2023 4 hours ago, Hemi Joel said: A regulator maintains the same pressure regardless of flow. A partially closed valve does not. Say for example you have an electric fuel pump in the back of the car by the tank and it generates a pressure of 7 PSI. But your old carburetor will only tolerate 3 PSI without pushing fuel past the needle and seat and flooding the carburetor. If you close down the valve so that you have 3 PSI at idle, it will be almost completely closed. When you apply throttle and the carburetor needs more fuel, not enough fuel can get through that tiny opening at the valve and the carburetor will starve, stalling the motor. If you open the valve enough to provide sufficient fuel at full throttle, then the large opening at the valve will not squelch the pressure enough at idle to prevent the car from flooding. A regulator has a built-in valve that is controlled by a diaphragm that is sensitive to fuel pressure on the outlet side. So when pressure on the outlet side begins to drop, it opens the valve more. And vice versa. I like this one because it's easy to adjust with no tools, it has a dial that is marked in PSI for adjusting it, it is reliable, and is on the low end of the cost scale. https://www.summitracing.com/parts/mrg-9710 I have never had good luck with those cheaper regulators. They always seem to fail prematurely and they never seemed to keep a steady pressure level. I now use a Holly regulator that was every bit of $100 about 10 years ago. I'd have to look at the car to get the part number. But then, I only use the electric fuel pump to prime the carb, then the electric fuel pump gets shut off and the car runs on the mechanical fuel pump. Edinmass has nothing good to say about those cheaper regulators and he was one of the reasons I switched to a more expensive, higher quality one. 1 Link to comment Share on other sites More sharing options...
Max4Me Posted November 10, 2023 Share Posted November 10, 2023 When I bought my 20's era car it had an electric fuel pump and pressure regulator installed. It never held a steady pressure. I replaced the regulator twice and both times the diaphragm ruptured, which then flooded the carb. So I decided to jump in and replumb the vacuum fuel tank. I took it as much apart as practical, cleaned, new gasket, and reassembled. Except for a minor leak at the tank bottom (which was recently fixed) it works like a charm. I'm not a fan of electric pumps, but I guess they serve a purpose at times. I agree with zephyr-spend the money to get a good regulator or you'll spend less money time and again to replace a cheap one. Link to comment Share on other sites More sharing options...
Frank DuVal Posted November 10, 2023 Share Posted November 10, 2023 4 hours ago, nat said: OEM equipment will deliver fuel at the correct pressure I see you are not buying new Corvair fuel pumps! 😱 The springs in the new ones are not made to the original specs and there are reports of them producing up to 9 PSI! A little much on that small needle and seat. And no, AC has not bought and relabeled an Airtex pump in many years, since Airtex quit making them. 😧 Link to comment Share on other sites More sharing options...
Mark Shaw Posted November 10, 2023 Share Posted November 10, 2023 18 hours ago, dl456 said: Hello Mark, I am glad you had good success with the regulators. The last regulator that I threw out was on a 1920 Studebaker, 289 cu in., single barrel Stromberg. Dennis Dennis, 289 cu in is a much larger displacement than any of my teens or 20's cars. That is probably why the cheap regulators didn't keep up. Mark Link to comment Share on other sites More sharing options...
dl456 Posted November 11, 2023 Share Posted November 11, 2023 Hello Mark, It was not a blanket condemnation of pressure regulators. My point was just a caution that you could create a problem much harder to diagnose than the one you are trying to solve. Thanks, Dennis Link to comment Share on other sites More sharing options...
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