Ok, here is my report. I checked the throttle plates and they are indeed closed when throttle at idle. I had another carb I tried and that carb had its idle slots not covered as much as mine. My carb was like the picture you sent on the right just a small amount of slot exposed. Ran engine down to 600 rpm and fuel out the Venturi is less but still there. I have installed new float,needle and seat and even new mechanical fuel pump and fuel pressure regulator set at 5 psi. The only thing I have not replaced is the idle tubes in the carb. I ran small wire down each ,soaked overnight and sprayed carb cleaner to clean. Carb cleaner comes out the fuel metering wells so I think they are clean,but maybe not. The engine starts easy and runs well at 1000,2000,3000 (all power settings) I did a run last week and burned 6 gallons/ hr for 25 miles. I have a semi displacement so 13 knots is about max and for a Mercruiser 260 hp inboard that’s seems pretty good. Any other ideas?
