Originally Posted by
Truckracer
Please refer to posts 5 and 6 above. Are you sure the pump diaphragm is installed correctly as from your description, it in incorrect. Perhaps you just mis-spoke regarding diaphragm / gasket placement. The pump diaphragm is under the heavy cover retained by the large single screw. The regulator diaphragm in under the cover retained by (4) screws. If pump pressure is low or non-existent, the engine can still run with the choke closed a bit or with needle settings opened farther than normal but it won't run right.
According to the welbro carb parts breakdown I have the diaphragm on the side of the metering valve is called the pump diaphragm and as I said it is next to the cover with the thick gasket next to the carb. The diaphram on the other side where the fuel enters the carb and then passes through the little screen is called the valve diaphragm and it is next to the carb body with the thick gasket next to the cover.
I can see we are saying the same thing but using different terms. Thankyou for making sure I was doing it right.
I spoke with the techs at Desert Aircraft, and they agreed the reed valve could cause the problem, we troubled shot it over the phone and with their guidance we eliminated the ignition battery, and the spark IC as possible problems. They did however say that there could be a very small piece of trash stuck in the high speed circuit and that I needed to be very sure that it is cleaned out.