Fuel Pump/Pressure ??? |
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JR_VIC ![]() Senior Member ![]() Joined: June-05-2006 Location: United States Status: Offline Points: 175 |
![]() ![]() ![]() ![]() ![]() Posted: November-19-2006 at 8:32pm |
I searched around and can not find a chart for recommended fuel pump PSI relative to horsepower and/or top RPM. Something such as approximate recommendations for example 300-350 horsepower or 5K RPM would be 5-6 PSI and 350-400 horsepower 5,500 RPM would be a range of 6-8 PSI. I am doing some trouble shooting and want to make sure my fuel pump is working properly. I installed a new intake last week as well as a new power valve in the carb. Took the boat out Saturday and the boat ran good up to 5050 RPM where it had an occasional cutting out or missing...almost like the rev limiter but not a consistent miss like a rev limiter feels. I checked the timing before I left and it was 12 degrees.
On Monday I am going to get a gauge and verify fuel pressure as well as pull the bowls and check for any debris. Total rebuild on the carb in April and new fuel pump in August. Last trip out in the boat before the intake swap the boat ran great with no problems and up to 5180 RPM with no cutting out/missing. If anyone knows where the fuel pressure should be that would help. Carb is a 4160 Holley 600 CFM. Any thoughts as to what else I could check would help. Timing was good but if I was running low on fuel pressure and the secondary bowls were running low I would think the engine would slowly loose RPM's and speed and not just a sudden miss or engine cut out. Thanks! |
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Tim D ![]() Grand Poobah ![]() Joined: August-23-2004 Location: United States Status: Offline Points: 2641 |
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The float could be a little low and you're running out of fuel. Why are you wanting to run 5,000 plus rpms?
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Tim D
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TRBenj ![]() Grand Poobah ![]() ![]() Joined: June-29-2005 Location: NWCT Status: Offline Points: 21195 |
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Because he can! Hes already running an Acme with extra cup. |
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SS-201 ![]() Senior Member ![]() Joined: October-20-2003 Location: United States Status: Offline Points: 105 |
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5-6 lbs over that you will need a regulator. The best way to check is while your moving under a load. The best way is to run a retun system.
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SS 201
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JR_VIC ![]() Senior Member ![]() Joined: June-05-2006 Location: United States Status: Offline Points: 175 |
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Although I do have a few barefooter friends who like to go upper 40 MPH range I am with TRBenj...I do it because I can.
SS-201...I'll check today for the 5-6 PSI range. I am vaguely familiar with the return style fuel rails/system on vehicles but don't anything about it on a carb application. Can you explain it in a little more detail? Any books you know of that I could read that goes into detail about it? Thanks! |
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Tim D ![]() Grand Poobah ![]() Joined: August-23-2004 Location: United States Status: Offline Points: 2641 |
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On cars, the electric fuel pump runs wide open, regardless of speed. The fuel regulator sends the un-needed fuel back to the fuel tank.
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Tim D
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SS-201 ![]() Senior Member ![]() Joined: October-20-2003 Location: United States Status: Offline Points: 105 |
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Yes,
The return side of the regulator goes to the tank the return line is approbate 1/2 less than the intake line. To be sure with the regulator wide open return the return should show about 2 lbs. The return line is the right size . Now you can regulate the pressure going to the tank to 5,6 lbs. What this does is control the fuel pressure to be a constant flow meeting the engine the demand for fuel. aand moving in a everlasting circle, also cooling the fuel This is done this way because at times the engine may need 10 lbs of pressure ,this way you never have to worry about lean fuel pressure. EFI engines do use this style as do all out race and or performance engines. |
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SS 201
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63 Skier ![]() Grand Poobah ![]() ![]() Joined: October-06-2006 Location: Concord, NH Status: Offline Points: 4288 |
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Before going to a lot of fuel pump and pressure trouble shooting it doesn't sound to me like that's the problem. Occasional misses are most likely ignition related, not fuel. I'd start with the ignition system, simple stuff like plugs and wires first. A bad distributor cap can cause high speed misses. Not sure what you are running but I'd start with on the ignition first.
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'63 American Skier - '98 Sport Nautique
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JR_VIC ![]() Senior Member ![]() Joined: June-05-2006 Location: United States Status: Offline Points: 175 |
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I was able to check the fuel pressure and it was @ 6 PSI so all is OK there. What is weird is that I am running a rev limiter with a 5600 RPM pill. With the Edelbrock it turned near 5200 RPM with no misses. Changed the intake and it is missing at 5050 RPM with the same 5600 RPM pill. Went to the lake and decided to install a 6000 RPM pill to see what happens and bingo...engine now turns 5400 RPM which again is strange so there must be an issue with the rev limiter even though it is only a few months old.
I then worked on the carb checked the screen and primaries for any debris but it was all clean. I then installed my rear secondary metering block conversion with size 70 jets upon Holley's recommendation. That must not be enough because it leaned popped at 5400 RPM so I did a plug chop and pulled all 8 plugs. Each plug was milk white in color so it appears lean on the top side. Also slightly raised the rear float but it did not appear to change anytihng. A little hesitation out of the hole so it appears lean all the way around. I'll keep tuning and get her dialed in. Thanks for all of the feedback |
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"That's not a Snow Cone that's my Ring!"
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JR_VIC ![]() Senior Member ![]() Joined: June-05-2006 Location: United States Status: Offline Points: 175 |
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Sorry...double post.
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"That's not a Snow Cone that's my Ring!"
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