Repurposing Mercury Outboard Vapor Separator

[xcookpac]

From http://www.bbcboards.net/showthread.php?t=748235&p=7699934&viewfull=1#post7699934

"Outboard gasoline motors generally have a vapor separator. The vapor separator accepts fuel from a low pressure pump which enters the vapor separator through a needle and seat. After the fuel passes through the needle and seat, the fuel is held in the reservoir (analogous to a carburetor bowl) where the fuel is available to the high pressure fuel pump. The needle and seat are controlled by a float assembly."

I am still in the planning stages for the conversion of my 1985 El Camino to TPI fuel injection. I am considering the following with regards to fuel supply to the fuel rail/injectors:

i.) installing a low pressure electric pump on the frame near the tank to supply fuel to the vapor separator reservoir (or perhaps just use the existing mechanical pump on the 305 to feed the vapor separator);

ii.) installing the vapor separator on the inner fender well to supply high pressure fuel to the TPI fuel rail (and ultimately the injectors); and

iii.) routing fuel return line from rail to the vapor separator.

Has anyone done such a fuel system conversion?

If so, how did it turn out?

Any insight/critique into this vapor separator solution would be appreciated.

PS Pics of Mercury fuel separator and applicable patent diagram attached.

PPS I already have one of these Mercury vapor separators kicking around (thus no cost to me).

[steveo]

keep in mind things can get pretty hot in those VSTs. a lot of outboards i work with have a liquid-to-liquid fuel cooler in the loop to keep things under control. it'll work fine if you don't out flow that little pump (watch for pressure drop at WOT)

[In-Tech]

Yeah, the VST wasn't such a good thing and why Mercury went to "cool fuel system" as mentioned above.

[xcookpac]

Thanks. I will try the vapor separator when I get to that point in my project and let all of you know how it goes.

[tayto]

https://www.opgi.com/el-camino/L241054/

why not just run an in-tank pump and be done with it? you're system sounds over complicated and unnecessary.

[xcookpac]

Tayto:

After rethinking the vapor separator issues presented (namely, fuel getting hot and also a fire hazard under the hood) I have decided to run solid stainless supply and return lines while using a 1987 Camino TBI tank and sending unit (with a Camaro fuel pump).

Vapor separator unit ("VSU") hookup is actually quite simple: i.) output from the mechanical fuel pump flows to the VSU; ii.) fuel in VSU reservoir is pumped by high pressure pump contained in VSU to fuel rail; iii.) fuel rail return is plumbed to the VSU. VSU eliminates new tank, new fuel lines, new sending unit and new fuel pump in tank. Downside: i.) hot fuel; ii.) extreme vapor pressure due to hot fuel which may not be able to be handled by carbon canister and vent; and iii.) fire hazard under the hood (VSU fuel reservoir could rupture in an accident and cause a huge fire or excess gas fumes could ignite if not effectively handled by carbon canister and vent).

PS I am going to use the vapor separator for when I run the TPI engine on the engine stand.

[1project2many]

You may be worrying more than OEM engineers. 1987 vehicles with EFI did not use special components as you are describing. If needed you could install a fuel cooler on the return line. I have done this with success.