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Dominick
Dominick, Marine Mechanic
Category: Boat
Satisfied Customers: 1009
Experience:  25 Years Experience as Mechanic, 20 Yrs Boat Yard Owner/Mechanic, Factory Certified
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I have a 5.0 Volvo penta that backfires thru the carb under

Customer Question

I have a 5.0 Volvo penta that backfires thru the carb under a load after 2500rpm. it has a Holley 2bbl which I have gone thru and I have tried several power valves with the same results. any clue
Submitted: 2 years ago.
Category: Boat
Expert:  Tan replied 2 years ago.
Hello. Yes a fuel restriction or water in the fuel. Remove the fuel filter and dump the contents into a clear container. Do you see a line of separation?If no water go to the next step. Run the engine on a different fuel source. This will tell us if you have a fuel delivery issue from the boat side fuel system or the engine. Does the back firing stop?
Customer: replied 2 years ago.
Tried that
Expert:  Tan replied 2 years ago.
Which? Both then have you checked the ignition timing? Have you done a compression test?
Customer: replied 2 years ago.
Yes ,replace the spark plugs also and they looked great. In neutral out of the water it has no problem. So that is why I chased the power valve.
Expert:  Tan replied 2 years ago.
The engine won't show a problem with no load. Yes you did compression test or checked the timing. You have to be more specific on what you have done yes doesn't tell me anything as to what you have or haven't checked. I need compression numbers. When you say tried that which fuel filter or running on another fuel source.
Customer: replied 2 years ago.
125 compression within 10% on all 8 cyl. Replace water separator filter. Distributor has never been touch lock in place .ran a portable can to the water Sep. Timing was at 5 degrees at 800rpm
Expert:  Tan replied 2 years ago.
Ok we need to check fuel pressure at the carburetor. Could I get the complete engine model number please. You should have more letters after the GL-???
Customer: replied 2 years ago.
5.0 gl_f. (###) ###-####R012168743
Expert:  Tan replied 2 years ago.
Some of these fuel pumps had a small screen in the inlet of the fuel pump. This will get clogged and restrict the flow of fuel to the carb. The screen is inside the fuel pump under fitting # ***** Look for blockage in that screen. Check fitting # ***** for an air leak.http://www.marinepartseurope.com/en/volvo-penta-explodedview-7745***-**-****.aspx
Customer: replied 2 years ago.
It's clean
Expert:  Tan replied 2 years ago.
Ok only thing left is fuel pressure. You should have around 6 psi at the carb.
Expert:  Tan replied 2 years ago.
Let me ask you this did you clean the carb or just replace the power valve?
Customer: replied 2 years ago.
Clean the carb twice! It was clean both times.
Customer: replied 2 years ago.
Pressure was almost7
Expert:  Tan replied 2 years ago.
Did you replace the base gaskets between the carb and intake?
Expert:  Tan replied 2 years ago.
Can you put a piece of clear hose between the fuel pump and carb? Look for air bubbles.
Customer: replied 2 years ago.
I replaced all the gaskets! I will have to make something up for the hose because it has crimp on fittings
Expert:  Tan replied 2 years ago.
Yeah I know they are a pain to deal with. Go to the parts house and see if you can get a fitting that will allow you to adapt. We are running out of things to check. Typically back fire is a lean fuel condition. If it were a valve the compression would be bad. We eliminated the fuel starvation from the boat side fuel system. The only thing that is left is an air leak. The water separator filter could have an air leak. Fuel starvation or water in the fuel.
Customer: replied 2 years ago.
Easier said then done. Nearest parts house is 18 miles away one way. I have been doing this for 40 yrs also!
Expert:  Tan replied 2 years ago.
Ok let me know what you find.