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HP 500 running out of fuel above 4000RPM

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Old 03-25-2012, 08:26 PM
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Default HP 500 running out of fuel above 4000RPM

Boat is a 21 foot Schiada River Tunnel with a 96 HP 500 and here are the symptoms. When going above 4000RPM the boat acts like its literally runs out of gas, and dies. I can crank it right back up and it will run fine again until starting to get over 4000 and then is when it acts like its running out of fuel and dies. Over the winter I replaced sea water mounted fuel pump as the diaphram had gone bad and the resivoir was full of gas. The carberator was also rebuilt, I also found out I incorrectly put in an extra quart of oil that will be coming out regardless. My thoughts on potential issues are, The floats in the carb aren't set right, I got a bad fuel pump, The cam that drives the fuel pump went bad due to lack of lubrication, the extra quart of oil triggers something that shuts the engine down, or I have a clogged fuel line(I've read this can happen to rubber hoses in boats with ethanol now in gasoline. Any advice or insight on where to narrow my search( or someplace I am over looking) would be greatly thankful
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Old 03-25-2012, 08:32 PM
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run it till it dies out and then look down the carb as you open the throttle to see if the accel pumps squirt or not. if you see no squirts then you know the carb is running out of fuel and can rule out ignition issues. holley carb i assume??
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Old 03-25-2012, 08:38 PM
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Yep its the stock Holley.
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Old 03-25-2012, 08:41 PM
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I had a similar issue last year. The diapham in the fuel pump was bad and little bits of it ended up in the needle and seat. My issue was also at 4000 rpm which was when the secondaries opened up. Do what roughwater suggested, when the engine dies go back to the carb and manually open it and see it it squirts fuel. If not you located your problem.
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Old 03-25-2012, 08:46 PM
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easy thing to do is a simple fuel volume test with fuel line in a safe container. do a idle and high speed test but its kinda risky as you could start a fire. make sure you have a good fire ext near and a helper. i have a even better idea but its flat dangerous so ill keep that one to myself.
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Old 03-25-2012, 08:46 PM
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#1 you prob didnt need a fuel pump its very common on the sea water pump mounted pumps to fill that cavity with gas it doesnt mean the diaphram is bad .it should be serviced every year drained and refilled with hp gear lube .#2 almost bet your prob is the fuel line into tank. their is a valve inline that is usually the culprit it can be removed and replaced with a std nipple the orig will have a ck ball and spring in it .#3 if you the boat till it dies and you pump acc pump it will still show fuel as their is a small cavity in the bowl for the acc pump charge .your best bet would be a fuel press gauge in the press side that will remove all dought .should see 5- 6 lbs press .hope this helps
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Old 03-25-2012, 08:52 PM
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even if the float bowl goes empty,there is still enough fuel for the acc pump to squirt some fuel,instead,try removing one of the bottom float bowl screws and catch any fuel that comes out in a cup.
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Old 03-26-2012, 06:32 AM
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When it starts to fall on its face....did you back off the throttle and see if it catches back up and stays running ? Open the fuel cap and try running it again. The vent in the tank may not be functioning properly sir. Just another idea to look at.
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Old 03-26-2012, 06:33 AM
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It wouldn’t hurt to check the anti-siphon valves that go to the fuel tank. I know My 502 mpi’s would run great and then fall on there face above 4000 rpm, ended up being debris in the anti-siphon valves.
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Old 03-27-2012, 07:18 AM
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does it just shut right off ? or surge then die ? would have to loose ALL fuel just to die..don't overlook ignition issues..
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