That's it, the flow guide valve.  It is not connected to the crankcase, so it is simply venting to atmosphere.  It is connected to the tank vent line and air filter box.  I recall cleaning it up a few years ago, maybe it is stuck again.

So, have purchased two replacement mechanical pumps and neither worked longer than 30 minutes out of the box.  So, I kept the marginal working one and added the electric.  So, what is the best mechanical pump to purchase and from whom?

If I needed one today I'd get this one...

https://www.amazon.com/GMB-550-8040-Mechanical-Fuel-Pump/dp/B00P2HS61Q/ref=sr_1_2?keywords=240z&qid=1581097676&refinements=p_36%3A1253494011&s=automotive&sr=1-2

I have a cheap stamped together one from O'Reilly's that has been good for 4 or 5 years.

1 hour ago, David F said:

So, have purchased two replacement mechanical pumps and neither worked longer than 30 minutes out of the box.

So, what is the best mechanical pump to purchase and from whom?

What brands are the two that failed and how did they fail?  What broke?  Pictures always good.

One was a Delphi MF0139 from Rock Auto.  The other was a Spectra Premium from Autozone A1203MP (this pump was identical to the Delphi regardless of what a Google search indicates).  Both pumps were similar in appearance to original (i.e. screw top).

Both initially worked fine for about 15 minutes...then stopped pumping.  Pulled pump operated arm, nothing to very little suction.

Edited February 7, 20205 yr by David F

Is the eccentric collar on right and still has the backing plate on? I think that's what it's called, the fuel pump's arm rides on it and moves in and out. The cam sprocket first then this thing. Tightn the holly hell out of that bolt too. Don't remember the ft. lbs. number right off but it's way up there.

10 hours ago, David F said:

That's it, the flow guide valve.  It is not connected to the crankcase, so it is simply venting to atmosphere.  It is connected to the tank vent line and air filter box.  I recall cleaning it up a few years ago, maybe it is stuck again.

Yeah, if the pressure in that tank vent line gets about 2psi above the crankcase connection, it's supposed to burp the excess pressure off. If it has stuck in the past, I give strong money that it's stuck again. I've never opened one up, but from the pics and the description, it's just a couple springs and sealing balls inside.

16 hours ago, siteunseen said:

Is the eccentric collar on right and still has the backing plate on? I think that's what it's called, the fuel pump's arm rides on it and moves in and out. The cam sprocket first then this thing. Tightn the holly hell out of that bolt too. Don't remember the ft. lbs. number right off but it's way up there.

The pump eccentric is fine.   As I mentioned, when I pull the non working pumps, they don’t pump when operated by hand.