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fuel line and pump sizing for 600 hp

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Old 11-30-2009, 03:31 PM
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Default fuel line and pump sizing for 600 hp

I have learned the hard way my fuel system was not adequate for the motor i'm running. I was hoping for some sage advice on fuel line sizing and gpm pump. I have a 60 gal tank with a siphon 5/8 tube. It is @ 18" up with a mandrel bend going thru a 3/4 ball valve then #8 AN to a aeroquip 10 micron filter. I have a mallory 110 gpm. pushing #8 to a 750 demon carb. The pick up tube was way to small the first go around at 3/16" with a very restrictive valve. Is this enough?? I really don't want to spend any more money and run return lines etc.
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Old 11-30-2009, 03:56 PM
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You have plenty now.
You did not mention the tank vent. It should be 1/2"-5/8"

On a side note...Coast Guard fuel rules do not allow a return fuel line so it would not be coast guard approved. Also a electric fuel pump has to be within 12" of the block. You are also not allowed to use stainless braided line. They make a plastic braided line that is CG approved.

Check your insurance policy about the boat having to meet CG requirments. If you ever have a problem you likely would not be covered.
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Old 11-30-2009, 03:57 PM
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You need to put a mechanical gauge on it and verify that it maintains 5 lbs. WOT.

If you have never had an O2 sensor in the exhaust, you may want to look into it. Fuel PSI and volume arent going to fix your problem if the carb is not right.
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Old 11-30-2009, 04:01 PM
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The vent line is 5/8" and the pump is just below the block mounted to the stringer. Bummer about the stainless. The power squadren did not catch that on my vessel inspection. Where is the best place to buy the correct lines. That's the last thing I need is hagerty saying nope to a claim.
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Old 11-30-2009, 05:20 PM
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They usually won't catch these type of things. The only thing they ever look for is a CG approved flame arrestor. One of the worst is standard carbs instead of marine. I woud be most guys in the CG (doing inspections)would have no clue what a J tube is.

This is there marine hose:
http://www.aeroquip.cc/aeroquipaerospacemarinehose.aspx

I think summit sells it or you can buy from the link.

Your mallory pump will likely hold a little over 6.5psi at WOT. Good to check as mentioned.
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Old 12-01-2009, 09:06 AM
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Yeah, I agree that I need to run pressure to the helm and watch. It is a demon marine 750. That thing is the most tempermental carb to dial in. It was running too rich on the idle circut. I think it is finally dialed in.
Thanks for the input.
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Old 12-01-2009, 10:32 AM
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Loose the check valve and get a 1/2' pickup. 3/16" pickup would feed my lawnmower not a 600 hp engine. I have learned also the hard way to over kill the fuel supply. For sure get a fuel pressure gauge and monitor it at WOT for pressure.
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Old 12-02-2009, 01:29 AM
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I would recommend an-10 (5/8") to the pump, and an-8 (1/2") to the carb.
Loose the check valve.

Chris

Last edited by CB-BLR; 12-02-2009 at 01:31 AM.
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