Merc 305 Running rough when warm

[bronko69er]

Never give up! More info: I pulled the carb again and started turning up the magnification on my diagnostics. I've confirmed that the float/needle and seat are working properly. I attached a hose to the carb and filled it with fuel, leaving 1ft of fuel/tube height worth of pressure above the carb. This did not create any leaks, so I decided to crank up the pressure. I attached a large syringe to the fuel hose and started pushing. It took a bit of effort but I was able to overcome the buoyancy of the float and unseat the needle. I do not have a pressure measurement of what this took, but it seemed pretty substantial. This makes me question the fuel pump. I found this thread: http://forums.iboats.com/forum/engin...=1504282397656
Make me want to install a gauge and see what the actual pressure is.

 

[alldodge]

You may have to much pressure, don't know it was mentioned back on the first page. You still have a problem with being unable to adjust the mixer screws.

 

[bronko69er]

Indeed you did mention fuel pressure on page 1. I overlooked it because I was unaware that pumps can fail by going too high and I knew there wasn't a shortage of fuel. When I over pressure the needle, the fuel leaks out the primary venturis/jets in the main bores, so perhaps this could be making up for closed needles. The needles look clean and corrosion free and appear to seat firmly. Gauge coming next.

 

[QBhoy]

Did you try disconnecting the auto choke, by turning it and locking off ?

 

[bronko69er]

Did you try disconnecting the auto choke, by turning it and locking off ?

The choke is working properly, and I've already ruled out the choke having anything to do with the problems.

 

[QBhoy]

Excellent. Just trying to think of the Simple things.

 

[bronko69er]

Dead headed the fuel pump with a gauge. 6psi when cranking. :/ The search continues.

 

[bronko69er]

New data: Borrowed a friend's good working Quadrajet and the behavior didn't change. Took apart fuel pump for curiosity, everything appeared super clean and functional. Drat.

 

[bronko69er]

Any other crazy ideas? Gonna start chasing down the electrical rabbit hole next.

 

[alldodge]

Sorry but have nothing. Reading back thru all post I see compression, timing, fuel pressure, air, voltage and nothing is wrong but it still does it