Troubleshooting Mechanical Fuel Pump?
Printed From: CorrectCraftFan.com
Category: Repairs and Maintenance
Forum Name: Engine Repair
Forum Discription: Engine problems and solutions
URL: http://www.CorrectCraftFan.com/forum/forum_posts.asp?TID=871
Printed Date: June-12-2024 at 11:53am
Topic: Troubleshooting Mechanical Fuel Pump?
Posted By: marks
Subject: Troubleshooting Mechanical Fuel Pump?
Date Posted: September-30-2004 at 4:30pm
Can a mechanical fuel pump test out okay at idle but still have problems at high RPM?
More specifically, my boat is showing some symptoms of fuel starvation at high RPMs when under some load. I tested the fuel pressure and volume at 600 rpm and it was okay, 6psi and .75gpm. Could the fuel pump still be the cause or should I be looking elsewhere? Its the original pump with 960 hours on it.
BTW, the carb only has 50 hours on it and I did check the screen in the carb inlet fitting.
Thanks,
Mark
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Replies:
Posted By: SS 201
Date Posted: September-30-2004 at 7:26pm
First what did you do to create this problem, or did it just appear?
Look elsewere, add octane booster run the boat in the water it will turn the plug tips red. If the plugs remain white or the same as they look now, you are lean. The only positive way to check pressure when running is to have a guage.
Under loads the carburetor demands different amounts of fuel, to elimate the demands they install a return fuel system like fuel injection.
However I'm sure you don't need this system, only for high performance.
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Posted By: Guests
Date Posted: October-01-2004 at 12:57pm
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Some boats have a cone-type screen where the tank outlet is, where the dip tube screws to the elbow...a clog there will show symtems at max fuel rate, first.
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Posted By: marks
Date Posted: October-01-2004 at 3:33pm
The problem started to appear about 4 weeks ago. At first I suspected bad gas or water in the gas, because it was after the one and only time this year that I purchased gas from a marina. Since then I changed the fuel filter and checked the inlet screen in the carb. I will take a look in the tank for an additional screen. I sort of assumed that good flow during the idle test would indicate that the fuel lines were clear.
The problem goes like this. If I have 3 or 4 adults in the boat, I can easily open it up and push the boat to 4400 RPMs. However, I have one friend that is a hard-core barefooter. He likes to stand up at 38mph, but once he is up he wants to speed up to 41mph for one-foot tricks. The boat used to be able to handle this. But now, when I open it up at 38mph (about 3900RPMs) the boat momentarily increases speed, hesitates, then settles in at about 39mph. If I hold the throttle full open, the engine will continue to hesitate every so often and the RPMs won't exceed 4000.
I didn't know if mechanical pumps could drop in pressure during high RPM's.
Thanks,
Mark
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