1994 Force 90 intake fuel recirculation question

[cjslapshot]

I just posted a new topic a few hours ago but I don't know what happened to it so her it goes again.

1994 Force 90hp Outboard. Runs great but I found that there is a small fitting on the bottom of the plastic intake cover. The intake cover collects the fuel that spills out from the carbs when the engine is tilted. My fitting is not connected to anything and I am a little confused when it comes to where the fuel is supposed to go. Currently the fuel just leaks out into the cowling. I have attached a diagram below. The fitting that is on the intake is part "7". The line "9" is missing but I can get that in any parts store. What I'm worried about is part "10". This is a fitting with a "metering cup". Is it just a check valve? Where does this part go back into the motor? How is the fuel recirculated? A pump? Vacuum? I'm concerned with fuel coming back into the intake and air getting into the fuel system. I'm surprised that the engine runs great without this part in place. Any info would be greatly appreciated.

 

[Frank Acampora]

Part 7 is a simple 90 degree threaded fitting. The problem is that it is 1/8 NPT and you may not easily find it. The Metered fitting is just that: It is a straight threaded fitting again, 1/8 NPT. It has a specially sized hole in the center of it to keep from leaking air when there is no spit-back fuel in the bottom of the air box. It should be screwed into the bottom of the manifold below the bottom carb, on the starter side of the engine. It protrudes straight down and if you are not looking for it the fitting can be easy to miss.

Operation is thus: While running, the carbs always "spit-back" a little fuel/oil mix. This is inevitable because the reeds don't close instantaneously. The air box collects this spit back and channels it through the hose to the bottom of the manifold which is under a slight negative pressure. This negative pressure sucks out the spit-back.

HOWEVER, if the manifold fitting was straight through without a restriction (metering orifice) then when there was no fuel collecting in the air box it would be the equivalent of an air leak, disrupting the balance of the carbs and leaning the fuel mix.THUS: with the metering fitting in place, the engine could be run without the hose or air box with no ill effects.

 

[cjslapshot]

Frank,
Thanks so much for your input. I am thinking that it might be easier to put a metering valve inline with the hose instead of finding a metering 1/8 NPT fitting. Do you see any issues if I do it that way?


ALSO so based on what you are saying the bottom fitting must be in place or plugged completely, right?

 

[Frank Acampora]

Depends upon which bottom fitting you are talking about. Bottom of the airbox should (not must) be plugged so fuel/oil does not drip all over the cowling. The bottom of the manifold can be plugged and the engine will not even notice but of course you will not pick up spit back. If the metered fitting is in place you need not do anything.

Yes, it is acceptable to put a metering orifice inside the hose. Early Chrysler 2 cylinder engines did just that. on the "puddle drain" hoses.