Fuel pressure regulator question

[Deleted User]
[Deleted User]
edited November -1 in HUDSON
I am running Twin H on my newly rebuilt 308, 500 miles on it. I have a fuel pressure regulator which I have set at 4. THe gas mileage I am getting is AWFUL. On the last fill up, I have driven 86 miles on about 3/4 of a tank, I figure about 6 to 7 mpg. I have checked and rechaecked all of the settings and adjustments and everything is spot on. The car runs beautifully, starts right up, just cruises along. I have checked for leaks in the fuel system, nothing. I am also running a Clifford Performance Duel header but running into one exhaust pipe. The muffler shop assured me that the single pipe was big enough.

Is a pressure regulator needed on a 308 engine? If so, is my setting to high? I am really grasping at straws here.

Any insights on my gas guzzler?

Doug

Comments

  • GrimGreaser
    GrimGreaser Senior Contributor
    I think these WA-1's need only a psi or so, I have mine turned down all the way and get ~2psi.

    While we're on the subject... I just installed my Twin H, mine starts really hard in the morning. I've adjusted and readjusted the chokes. It seems to flood at the drop of a hat when it's cold. It, however, runs really good once I get it started and warm.
  • dougson
    dougson Senior Contributor
    I would look at the timing again. If it is running too much advance it will be too rich. I am told the header causes the engine to run lean and maybe you gave it too much advance? Also, are you sure the vacuum advance is working, if not it would require more gas to accelerate. Additionally, the old heat operated chokes on the WA-1s probably take a lot longer to fully open then a modern computer controlled car, also using more gas. Finally, I think these cars were geared far too high (numerically) for regular use. I am running a 5 speed and the rear gears are 3.91. I'm not on the road yet so we'll see if there is a real difference. I've also read that these engines with twin-H were guzzlers regardless and I would not expect much more 12 or 13 mpg.
  • [Deleted User]
    [Deleted User]
    edited October 2011
    Dougson, thanks for your response. The vacuum advance is new. I have got the timing set right on the long timing mark on the flywheel, no advance or retard. The timing was set with the advance disconnected, the car in gear and idling at about 600 rpm.

    Disregarding the gas mileage, I can't imagine this car running any better than it does now. This is a real puzzler.

    Doug
  • RonS
    RonS Senior Contributor
    edited October 2011
    Why do you have a pressure regulator at all? Are you running an electric fuel pump as primary fuel delivery? If so, what type and brand? If an elec pump is used as a primer only I don't believe you need a regulator. The mechanical pump should put out 4.5 -5 psi( a bit on the high side due to ethanol). With a proper rebuild, and adding, or removing a gasket on the fuel pump, you should attain at a good pump pressure . Same PSI for electrics, and that is where you may need a regulator. Of course the floats need to be able to hold the pressure from any pump. BTW, I don't recommend those dial in regulators, too many failures and leaks
  • [Deleted User]
    [Deleted User]
    RonS, that is the question; do I need a pressure regulator. The guy that originally rebuilt the carbs recommended it. ? ? ?. I have an electric fuel pump but only use it as a primer and a backup. Am running a duel action fuel pump. According to spec, I am supposed to be getting a vacuum reading of 17 to 21, but I am barely getting 16. Is that part of the problem? All the vacuum lines are new.

    Doug
  • Geoff
    Geoff Senior Contributor
    Does the vacuum alter with different advance settings? 16 is too low. It could be your valve timing out, but more likely the distributor. You definitely need to get it around 20.
  • bob ward
    bob ward Senior Contributor
    Dougc, your carb builder will certainly be aware of this, but double check that he has adjusted the float levels to allow for the lighter petrol that we use today.

    The lighter fuel means that your float sinks further down in the bowl than it did originally, hence the fuel level in the bowl becomes higher than it should be before the float can close off the needle valve.
  • GrimGreaser
    GrimGreaser Senior Contributor
    Okay, how much should the float adjustment be changed, roughly?
  • [Deleted User]
    [Deleted User]
    What rear axle ratio do you have?
    Have you checked the float levels?
    Do the chokes come off all the way?
  • RonS
    RonS Senior Contributor
    What is the elevation of your home? You will lose about 1 HG of vacuum for every 1000 ft. My Hornet is slightly over 18, but my home is 2400' elevation. It may also be a retarded timing as the other guys said, caused by the advance, dist setting or float level. I would think that some sort of fuel flooding or fuel leak would appear if there was such a fuel usage. What is your PSI in the fuel line at the carbs? You have two issues which may be related: too much fuel used and vacuum on the low side. Is the vacuum gauge steady 16 or bouncing? Are there any intake leaks in the carbs or manifold?
  • lostmind
    lostmind Expert Adviser
    A quick test would be to loosen the distributor hold down
    bolt and advance the timing to see if the vacuum goes up.

    Roy
  • dougson
    dougson Senior Contributor
    Interesting topic. Vacuum could certainly be (at least part of) the problem. We do need to know the trans. and final drive ratio. Low vacuum could be retarded timing or a leak somewhere, or both. I use the propane with a rubber hose and bicycle needle to test for vacuum leaks. Regarding electric fual pumps I am using a Facet electric pump exclusively with a regulator to keep the pressure around 2-3 psi (W. Mordenti warns that 3 or more psi is too much for the old WA-1, he's right, when I exceed 3 psi I get gas out of the vent).
  • Richard E.
    Richard E. Senior Contributor
    Does the twin H exhaust manifold have an exhaust damper in it? Make sure that it is operating properly. I had one in my '36T stuck shut and it played hell w/gas mileage, also gets very hot. Vacuum sounds like you might have a leak somewhere??
  • RonS
    RonS Senior Contributor
    edited October 2011
    Doug, I will say I do not agree with the 3PSI statement. First I strongly recommend the Craig valve for the float needle( see WTN), or at least replace the old solid brass needle with a viton tiped one. In the absence of that, the original shop manual in 1952, calls for 3-4 PSI on the AC. With the volatile fuels of today, I would go as high as possible on PSI, at least 4-5 due to pre vapor lock fuel starvation issues in warm weather. If the fuel does not push out of the float vent, especially the rear carb on start ups ,fine. My PSI gauge shows 5 Psi and no leaks at idle. More likely, float adjustment and, or timing are the culprits, baring stuck choke etc.
  • hudsonguy
    hudsonguy Senior Contributor
    Another variable to consider, along with your elevation, etc. is whether you have a Visor or not. I have one on my car, and even though it looks great, it's bound to drop my mileage at least a little bit. Any thoughts on how much difference this could make? I'm even thinking of taking it off temporarily the next time I do a cross country trip, just to save some money!
  • dougson
    dougson Senior Contributor
    RonS wrote:
    Doug, I will say I do not agree with the 3PSI statement. First I strongly recommend the Craig valve for the float needle( see WTN), or at least replace the old solid brass needle with a viton tiped one....

    With the these upgrades I agree that the pressure can be higher. I should install the Craig valves.
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