My ASP75 is fitted with one of the new series ST 75 carb for fuel economy, and the combo has always performed well. After recently replacing a split fuel tank and doing a carb strip down, I am having a problem keeping the engine running at idle.

The top end is fine, with a reasonable midrange which is typical of the ST carb, but is not a major problem.

The engine idles normally on an OS #8 plug with the starting battery connected, but as soon as the battery is removed the engine quits, yet it idles well with a Fox miracle plug when the battery is removed.

I have tried several new #8's with no change, what could be wrong. I would like to continue using the OS plug as it gives a good midrange response. I have checked all fuel lines for leaks and pressured the system, and used high temp RTV silicone to help seal the carb neck / engine to guard against a possible air leak.

What am I missing here ??