Gas line problem ?

[Bear]

Hi my 1986 f32 crusader 350s has four gas tanks when I put it on the rear back starboard tank for the starboard engine after running for awhile the engine starts to back fire Rpm go down like its starving for gas I put the forward tank on by itself or in combination with the rear it runs fine. All the same gas, I have switched to the other tanks and run the engine on them no problems, so I'm thinking the line running back to the tank is the problem but it's a copper hard line (assuming copper) is there an anti siphon valve going into the tank?? I thought about swapping the lines at the valves to eliminate the valve as a problem and work my way back to the tank process of elimination. Any thoughts?? Thanks Jim

[Big D]

Likely a problem with the anti-siphon valve. You can remove and clean it or simply replace it with a new one. It'll look like a regular fitting right at the top of the tank where the fuel line hooks up. Check if there is a fuel filter hidden somewhere along that line that may have been forgotten about and simply needs to be replaced. Also make sure your vent is clear and not blocked off by spider webs or something else. Easy enough to check if venting is the cause by opening up the filler cap when the engine starts acting up. If she starts running smooth right away, you'll know it's a venting issue.

[Bear]

Thanks the vent is clear I will check the anti siphon and check for any filters theres only one on the engine that I see that's something I want to add this winter

[larryeddington]

search anti siphon I posted pics of the disassembled valve and source for the original and another bran . Most AS valves have a hose barb. These are secured to the copper fuel lines with flare nut, which IMO is better.

[Bear]

Ok guys I took the check valve and found chunks of orange silicon I'm thinking its from the gas gauge someone may have used some kind of sealant it was like soft rubber like rtv cleaned it out started it, 10 min job, working on this f32 is a dream compared to my old boat this would of took an hour to get to fuel tanks on that boat. I couldn't go out very low tide moon tide I'll try it this weekend under load , going to change fuel filters this wknd thanks for the help Jim