Webers dumping gas in motor after shutdown
 

OK, I'm having an issue where after I shut down my motor some gas will work its way into the cylinders. I have noticed gas on some of the plugs and intake valves.

What I have done.

Newly rebuilt 3,0 with DC cams and JE 9.5 pistons

Weber 40s, rebuilt and rebushed. New insulator gaskets. K&N filters.

New needle and seats, twice. Floats set and the levels rechecked. Floats checked for free movement and operation.

Facet fuel pump. The solid state one.

Extra vent drillings per Bruce Anderson.

AEM air fuel gauge is installed. Mixture readings are good while the engine is running.

Oil temp readings are normal.

Thanks for any advise.

Fuel in fuel gallery from idle jet to idle mixture screw will drain fuel into cylinder after shutdown but this is a small amount.

I assume engine runs fine on the idle/progression circuit. I also assume "Lean Best" idle adjustment can be achieved on each cylinder. If no then check to see that gasket between top cover & main body does not block air correction jets for the idle circuit; these are the little brass jets that are about 3/16" in diameter & pressed into the top body just inboard of each idle jet location.

Also, check to see that the idle air correction jets are clear; their orifice diameter is 1.10mm for IDA and 1.40mm for IDTP Webers.

The Bruce Anderson/PMO float bowls venting scheme was developed by Ferrari for their 365BB & 512BB which used Webers. The point of the drilling is to vent percolating fuel into the throttle bore before it goes up the vent pipe & down onto a hot engine. I no longer utilize this venting method since it floods the idle circuit on the way into the throttle bore. I have developed an alternate venting method. A secondary downfall of the Bruce Anderson/PMO/Ferrari venting is that during high speed/G-loading cornering the fuel in the float bowl will flood the idle circuit on one bank of carbs which results in a rich stumble upon throttle application.

Check to see that fuel tank is vented, if not then internal tank pressure can overcome float needle valves & allow fuel to flood engine.

Hope one of these rectifies the issue, if not then when it is remedied I would like to know what the fix was.

Thanks Paul. My motor is out now, but in a couple of days I'll start through the list.

It may be the B.A. venting method allowing fuel in through the idle circuit. I will have to monitor how the fuel is getting out of the float bowls.

BTW, I was having another problem that required removing the lead shot plugs. There was a loose piece of flashing causing intermediate progressive problems. So suffice it to say I have already gone through the idle circuits. (more than once)

Also, as a side note, in order to get my part throttle cruise to a reasonable A/F number I went to 120 idle airs, which helped quite a bit.

Glad to hear you are not afraid of the Webers; removal of the lead plugs for gallery cleaning & tuning progression circuit with idle air corrections are good tools to have in your bag of tricks. I use .177 caliber lead pellets: dead soft & cheap.

Reminds me of the '70 beetle I own. If parked with it's nose on an incline, gas can sneak past the needle & seat. I would suppose Porsche has developed some kind of a valve to keep that from happening though...