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Carb HP 500's lack of Fuel above 3100 rpm?

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Carb HP 500's lack of Fuel above 3100 rpm?

Old 07-28-2017, 09:48 AM
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Default Carb HP 500's lack of Fuel above 3100 rpm?

Hi. I have a 1998' 32' Fountain with twin Carb HP 500's that were fully rebuilt 100 hours ago. Everything inside the motors are new but all the exterior parts were reused (pumps, carbs, intake, impellers etc). Took the boat out a few weeks ago and kept it at about 2500 rpm and under most of the day just cruising. A few hours later on the way home, I got on it a bit and noticed the boat kind of bogging down. I looked at the tachs and the port motor tach was fluttering like it was running out of gas. I brought it back down to 2500 rpm and everything was fine. I stopped, turned off motors and restarted and tried another WOT run but the port motor completely stopped once above 3500 rpm. Stopped boat, restarted and just kept below 3100 the rest of the way home and things were fine.
So definately sounds like it wasn't getting enough fuel so I wanted thoughts on how to troubleshoot. Could it be a clogged filter or something? If so, where are the filters?

Thanks in advance.

Jay
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Old 07-28-2017, 10:05 AM
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Start with the quickest cheapest easiest. The fuel pickup in the tank has a sock on the bottom of it. I had that same exact issue in an old IMP. Tore the carb apart, tore the fuel pump apart tore everything apart still would just run out of fuel at about 3,500. Back off to idle and let the float bowls fill, and you had about 3 seconds of Full Throttle before the thing ran out of gas again. Pull the pickup tube out cleaned off the sock ran like a champ. Then the other motor did it about one minute later. At least the second time it was only a five minute repair.
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Old 07-28-2017, 10:23 AM
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Originally Posted by dereknkathy View Post
Start with the quickest cheapest easiest. The fuel pickup in the tank has a sock on the bottom of it. I had that same exact issue in an old IMP. Tore the carb apart, tore the fuel pump apart tore everything apart still would just run out of fuel at about 3,500. Back off to idle and let the float bowls fill, and you had about 3 seconds of Full Throttle before the thing ran out of gas again. Pull the pickup tube out cleaned off the sock ran like a champ. Then the other motor did it about one minute later. At least the second time it was only a five minute repair.
Derek,

Thanks for that tip! I'll try that! Can you tell me how to get to the fuel pickup? Never messed around with any of that. Thx!
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Old 07-28-2017, 10:41 AM
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You should be able to see the back of the tank from front of engine compartment. You will see the 2 fuel lines going forward under the cockpit floor. If not visible there, look for a round deck fitting somewhere like under the back seat. Has to be some kind of access to mess with gas gauge and these pick ups.
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Old 07-28-2017, 10:49 AM
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Originally Posted by dereknkathy View Post
You should be able to see the back of the tank from front of engine compartment. You will see the 2 fuel lines going forward under the cockpit floor. If not visible there, look for a round deck fitting somewhere like under the back seat. Has to be some kind of access to mess with gas gauge and these pick ups.
There is definitely a round 6" access hole under the back seat for the fuel gauge. I thought it only had 2 wires going into it for the gauge only but I'll look again once back to the boat to see if there are also fuel lines. So on your boat those socks were clogged with junk? Did you just rinse them in water to clean and then put back on? Thx.
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Old 07-28-2017, 12:22 PM
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Fuel pump going bad. That's just about the rpm for it to show up. Check fuel pressure at that rpm and see what it is.

Mark
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Old 07-28-2017, 02:01 PM
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If it has the POS fuel pump setup off the water pump pull that and make sure the lube is still 90w and not full of fuel and is not eating itself up due to lack of lube, very $$$$ parts to replace
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