Carb guys and/or fuel issue
10-28-2015, 01:00 PM
#11
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10-28-2015, 03:38 PM
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Best to do that then to throw parts at her. If no tachometer bounce is noticed during the condition stay with the fuel diagnostics.
Hopefully there are some days for you there to take her out and try all that's been recommended by everyone.
10-28-2015, 08:16 PM
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just a dumb and out there thought but when you had stuff apart you didnt by accident hook the vent hose to a vacuum source? just asking as I have seen that before and if you pull a vacuum on the pump it will lay down and not pump much.
10-29-2015, 07:42 AM
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I went through a very similar problem this summer. When diagnosing with a fuel pressure gauge, remember that pressure does not equal flow. In my case, I was able to maintain between 5.5 and 6 psi while still starving the engine for fuel. It turned out to be too much restriction caused by the fuel filters at the carb inlet. They were not the correct ones, collapsed and severely limited the amount of fuel that could flow through.
On the dyno I ran to 6000 rpm fully loaded and in full marine trim, but was using the dyno's fuel pump. When installed on the boat with no changes other than fuel pump, I could not get over 3100 without starving. The aitrtex pump I used (I thought it was a merc equivalent) was not able to push enough fuel past the filters - Imagine trying to push a mouthful of water through a stirring straw, you can have quite high pressure with very little flow coming out the end.
Ultimately, I wound up buying a new merc pump, have the Keith Eickert base but not installed, and upgraded all the lines to -8AN (and removed the incorrect filters) It seemed to do fine with the merc pump and new lines so far without adding the upgraded bottom half.
Since you only have the problem on one engine, the line size is probably okay. Have you checked to see they are all clear from the pump to the carb? Are the filters in the carb okay? Partially collapsed? Lines clear? Could the fuel water separator be restricting the fuel available for the pump to push to the carb?
Ryan
On the dyno I ran to 6000 rpm fully loaded and in full marine trim, but was using the dyno's fuel pump. When installed on the boat with no changes other than fuel pump, I could not get over 3100 without starving. The aitrtex pump I used (I thought it was a merc equivalent) was not able to push enough fuel past the filters - Imagine trying to push a mouthful of water through a stirring straw, you can have quite high pressure with very little flow coming out the end.
Ultimately, I wound up buying a new merc pump, have the Keith Eickert base but not installed, and upgraded all the lines to -8AN (and removed the incorrect filters) It seemed to do fine with the merc pump and new lines so far without adding the upgraded bottom half.
Since you only have the problem on one engine, the line size is probably okay. Have you checked to see they are all clear from the pump to the carb? Are the filters in the carb okay? Partially collapsed? Lines clear? Could the fuel water separator be restricting the fuel available for the pump to push to the carb?
Ryan
Last edited by Ballistic Beak; 10-30-2015 at 07:13 AM. Reason: spelling
10-29-2015, 08:35 AM
#16
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I've also seen fuel hose collapse under suction if it is deteriorated from ethanol, etc.
10-30-2015, 05:49 AM
#18
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I went through a very similar problem this summer. When diagnosing with a fuel pressure gauge, remember that pressure dies not equal flow. In my case, I was able to maintain between 5.5 and 6 psi while still starving the engine for fuel. It turned out to be too much restriction caused by the fuel filters at the carb inlet. They were not the correct ones, collapsed and severely limited the amount of fuel that could flow through.
On the dyno I ran to 6000 rpm fully loaded and in full marine trim, but was using the dyno's fuel pump. When installed on the boat with no changes other than fuel pump, I could not get over 3100 without starving. The aitrtex pump I used (I thought it was a merc equivalent) was not able to push enough fuel past the filters - Imagine trying to push a mouthful of water through a stirring straw, you can have quite high pressure with very little flow coming out the end.
Ultimately, I wound up buying a new merc pump, have the Keith Eickert base but not installed, and upgraded all the lines to -8AN (and removed the incorrect filters) It seemed to do fine with the merc pump and new lines so far without adding the upgraded bottom half.
Since you only have the problem on one engine, the line size is probably okay. Have you checked to see they are all clear from the pump to the carb? Are the filters in the carb okay? Partially collapsed? Lines clear? Could the fuel water separator be restricting the fuel available for the pump to push to the carb?
Ryan
On the dyno I ran to 6000 rpm fully loaded and in full marine trim, but was using the dyno's fuel pump. When installed on the boat with no changes other than fuel pump, I could not get over 3100 without starving. The aitrtex pump I used (I thought it was a merc equivalent) was not able to push enough fuel past the filters - Imagine trying to push a mouthful of water through a stirring straw, you can have quite high pressure with very little flow coming out the end.
Ultimately, I wound up buying a new merc pump, have the Keith Eickert base but not installed, and upgraded all the lines to -8AN (and removed the incorrect filters) It seemed to do fine with the merc pump and new lines so far without adding the upgraded bottom half.
Since you only have the problem on one engine, the line size is probably okay. Have you checked to see they are all clear from the pump to the carb? Are the filters in the carb okay? Partially collapsed? Lines clear? Could the fuel water separator be restricting the fuel available for the pump to push to the carb?
Ryan
