Screw in Carburetor Return Line...why?

[bischof]

My 1995 OMC Cobra 5.0L with Holley 2Bbl carburetor was working great, then went into a few minutes of very rough idling, then refused to run anywhere near idle.

One of the 1st things I did (because it was easy) was pull off the PVC return line from the carburetor to the gas tank (which didn't seem to help/hurt my problem).

I was shocked to see a screw wedged in the tube, very near the carburetor port. Its head was 99.5% blocking the line (ie. no way it was sucked in from anywhere). Removing the screw from the line, didn't seem to help my situation either.

I assume the last person who rebuilt the carburetor put it there.

Can anyone think of a reason to do this? (I'm an engine & boating newbie, so be gentle).

 

[Howard Sterndrive]

Re: Screw in Carburetor Return Line...why?

there shouldn't be any return lines to the fuel tank on a carbureted engine.
There should be one SUPPLY fuel line coming out of the fuel tank, to the filter, then steel line to the pump and then another steel line to the carb. There should be an overflow line from the pump to the carb in case of diaphragm rupture.
The only other fitting on your fuel tank should be the vent.

guess#1:
Maybe your engine had fuel injection on it at one time, or maybe the boat builder rigged the hull for a fuel injected engine, and then the order changed to carb so they stuck a screw in the return hose and jammed it on some unused carb port.
There was a FI option for the 5.0 that year.
There was a guy here last year frustrated at the NLA fuel injection parts and was ripping the injection off his 5L and putting a used carb and intake on it. did you buy his boat?

guess#2:
Someone replaced your marine fuel pump with an automotive one and routed the safety hose back to the tank thinking that was accomplishing something. Then when vacuum started pulling fuel out it, jammed a screw in it.

Pics and/or a model number off the engine may help.

 

[bischof]

Re: Screw in Carburetor Return Line...why?



Here's a couple pics of the what I thought was the return line port (carb interior & exterior)
There's some blue text callouts that may be hard to see unless you zoom a bit.

I like the 'someone swapped out my EFI' explanation. ; )

Engine Model #: 502APHU

BTW, here's my guesses as to how this decodes:
50 = 5.0L
2 = 2 valve carb
A = version 1 of engine
p = power steering
HU = 1995
Also, some websites seem to have a 'E' or 'B' postfix. What are these?


* Ha! I just found a footnote on the original purchase paperwork that says, " + 5.0L EFI (model QI0I)"
Sounds like Capt Howard Sterndrive was right!