The fuel pumps in TCST were overwhelming the float and overflowing the carb with fuel. I bought a fuel pressure regulator that was rated for 1 - 4 psi ... it turned out to be chinesium E36 M3 and would not reduce pressure below 3 psi even with the adjusting screw removed! Since I wanted to get it started and like the KISS principle I made a T in the line and bled off pressure with a orifice ... it worked and the car runs!
Someone on another forum was concerned I was reducing fuel flow to the carb. I have two pumps, one comes on with boost (in theory one was enough but I didn't want fuel starvation). Pressure goes up .5 psi when the second pump kicks in and the carb is still happy with that.
A regulator also reduces flow and causes pressure spikes, it is deadheaded at times etc unless you get a bypass one ....
So if a bypass regulator is better why not just control pressure with a bypass like I have done? (The pumps are rated at 4 psi so it's not like I am bypassing a huge amount of fuel to get the pressure down.) The pressure seems fine and the pump pumps fuel continuously which makes the pump last longer, avoids vapor lock, pressure spikes etc.
Currently the bypass is before the carb inlet but I will move it to after it to give the carb "priority". I have an AFR gauge to monitor things ....
Comments?
In reply to TurboFource :
I'm confused because it sounds like you're talking about a carb, but you're approaching fuel pressure like it's a detailed tuning concern like it would be in fuel injection.
Fuel pressure regulators for carbs seem to be mostly pretty bad, and my impression is that you should just find a pump that works with your carb's pressure requirements.
As long as it can move sufficient volume, you're done. If your fuel pump is affecting your carb's fuel delivery, you have a problem. It needs to move enough fuel to keep the float bowl topped up consistently, and not overwhelm the valve and keep filling. The end.
I don't see a problem with doing it with a bypass, it just seems like unnecessary complexity. I won't argue with your observations about continuous flow, but plenty of systems exist both ways, and I suspect the low pressure/energy of a carb pump de-emphasizes some of those concerns.
The pump is for a carbed engine but Zenith Strombergs like low pressure, I was hoping to get away with no pressure reduction but that is not the case.
That's the thing, right? My impulse would be to find a lower-pressure pump, not just a "carb" pump. E.G. the SU-style ones. My MGB came with a Rochester (IIRC) pump and a Mr. Gasket FPR, and it is now happily returned to an SU-style (but electronic, not points) pump which is meant for these carbs that demand lower pressure (made by Hardi; very happy with the pump and the service, as the CEO answered my troubleshooting question when it turned out it had ingested a pebble from the ancient fuel tank two minutes after installation).
If you really want to pursue DIY fuel pressure regulation, I'd go all-in and go beyond an orifice to an actual pressure regulation valve. I mean, it's clear why you get the pressure bump when the second pump kicks in; you're trying to bleed off more fuel through the same opening. As long as it's below what the carb will cope with it shouldn't matter, but it still feels to me like you're introducing more complexity to the system and even your redundancy/over-capacity comes with a side order of variability in the form of a fuel pressure bump.
I'd look for a pump that's rated for Stromberg-friendly pressure and a power level that's everything your turbo'd engine can make to be sure of sufficient volume and call it done.
But that's just me. It sounds like you're enjoying the problem (er, problem-solving), and that's dandy, too. That's why we do this stuff, right?
Pump is supposed to be for cars with SUs, Solexes, Webers etc..... not a Holley etc.
In reply to TurboFource :
I don't know what to say to that.
It sounds to me like you have a pump that said on the box "compatible with Stromberg" or something like it but insists on putting out enough pressure to overwhelm the needle valve. That's not compatible. That just means the box was wrong or just flat lied, it doesn't mean that no pumps actually keep the pressure down to compatibility with these carbs.
Or you've got a dodgy/weak needle valve.
I believe your FPR system can work, I just don't know what to do with the implicit assertion that because THIS pump doesn't work with your carb that an FPR is necessary.
The pumps are well beyond the return to vendor point and they are hard to get to ( like most things on this tiny car!) so they will remain as I have decided time is of the essence. They may not be optimal but the AFR gauge will decide if they are reasonable. The second pump may not need to be ran but it is also there as I can switch the primary to the secondary pump with two easy to reach screws if the primary dies and then easily get home :)
Thanks for your input Jesse! I will check out the Hardi pump you meantioned for possible future use.
For what it's worth, carbureted RX-7s had a return line with a bleed orifice, I think to reduce the possibility of vapor lock.
As long as your fuel pump setup can supply enough volume plus what the orifice bleeds out, you'll be just fine.
I had issues with a cheap regulator last year. It was intermittently over-pressurizing, causing the engine to run like crap. I took apart the regulator and found machining shavings inside. Cleaned it out, put it back together, and that fixed it. Might be worth a look inside.
Chrysler and I'm sure others had a bleed orifice in the fuel filter (before the carb) to prevent vaporlock like Pete said. I ran one on my carbed 302 for awhile with no ill effects. If it works, run it.
Glad you got some more feedback/confirmation here.
Reading over, while I think "the right pump" is the simplest answer, I also think I didn't do a very good job of asking what you were asking, and I got very fixated on "fuel systems can wreak a lot of havoc and having two pumps and an FPR adds variables." Apologies for that; I've always hated it when people answer "how do I do this?" with "why on earth would you do that?" It just wasn't clear to me whether you were asking whether and how to do an FPR, or getting input on the general solution to reliable fuel pressure and volume.
