Re-circulation bleed system question

[Dave1027]

My '88 Merc 100 hp 4 cyl has a fuel hose that runs from the bottom cyl back up to the top cyl. I used a mityvac to test the orifices the hose is connected to. The bottom orifice/valve seems to function so that it lets the excess fuel out but closes the other direction. Sounds good I'm thinking.

My question is regarding the top. The top orifice lets air go both directions but is somewhat restricted. Is this normal for this orifice? It might be normal because it's up against the top bearing and this portion of the system already has the bottom valve for flow direction control.

 

[schematic]

Re: Re-circulation bleed system question

sounds normal, what the underlying problem?

 

[Dave1027]

Re: Re-circulation bleed system question

Intermittent high idle (2000 rpm) after cruising. It seems like fuel building up in the lower cylinders causing them to continue firing when they shouldn't.

 

[schematic]

Re: Re-circulation bleed system question

-throttle linkage/cable binding?
-throttle plates binding?
-timer base binding?
-fuel pump diaphram leak?
-idle stabilizer (if so equipped)?

 

[Dave1027]

Re: Re-circulation bleed system question

-throttle linkage/cable binding?
-throttle plates binding?
-timer base binding?
-fuel pump diaphram leak?
-idle stabilizer (if so equipped)?

Nope
Nope
Nope
I thought maybe because it's attached to the bottom two cyls so I rebuilt the pump. Didn't help.
Not applicable to this engine.

One other thing I should mention, when it does it, it runs high for about 5 seconds then coughs and returns to a normal idle. The cough leads me to believe it's burning off the fuel till lean then cough then no more firing.

Keep 'em coming. I'm open to any possibility.

 

[schematic]

Re: Re-circulation bleed system question

that sure sounds like throttles plates briefly stuck wide open. The cough would be retarded timing occuring before plates closed.