Can the fuel over prime vent mess up idling mixture?

[Will.iam]

Noticed the other day on shutdown no 50 rpm rise. I initially thought it was an induction leak so i pulled off the cowl and used a shop vac to pressurize the intake manifold while i used soapy water to check for leaks. I did not find any bubbles. But i decided to also check for any fuel leaks around the injectors so following continental’s guidance in their M-0 i used full mixture and 1/4 throttle. Turned on the fuel pump and looked. I didn’t see any leaks at the fuel injector but noticed 2 places fuel was dripping out one was the over prime vent hose but the other was where the metal tubes from 2, 4, 6 tee together and the drain tube from that tee the b-nut had came loose to where fuel was coming out of the connection. I tighten the b-nut back onto the tee fitting and retested the fuel primer to which there was no leak and then did an engine ground run and the idle had a 50 RPM rise on shutdown. I can’t believe this would make a difference as i thought that pluming is only used when you flood the engine and it allows a place for the fuel to drain out right? Or am i missing something or i do not understand fully what that fuel drain pipe system does in addition to fuel draining. 

[M20F]

I would have done another 50 rpm test after the first one as opposed to doing a lot of stuff then doing another test.  
 

[kortopates]

3 hours ago, Will.iam said:

Or am i missing something or i do not understand fully what that fuel drain pipe system does in addition to fuel draining. 

Yes, you just corrected an induction leak. Any leakage above the sniffle valve is no different than leakage in the induction plumbing. At the bottom of the engine is where the two aluminum tubes connect into the sniffle valve. The valve has a small plastic ball that when the engine is running is sucks the ball up to close off the line so air isn't being sucked in through the drain when the engine is running. But fuel can drain out and down when the engine isn't running since without the suction the ball falls down (but doesn't block the drain line).

Good job finding the leakage, most would not have even looked at the cylinder drains but they are a common source of leakage.

[Will.iam]

13 hours ago, M20F said:

I would have done another 50 rpm test after the first one as opposed to doing a lot of stuff then doing another test.  
 

Actually i had noticed the non 50 rpm rise on a couple of shutdowns to rule out it wasn’t a one time fluke.