Had to replace my intake manifold due to a rusted hole in the exhaust crossover. I believe this is a common issue. Put it all back together and it fired right up. The issue is that the Rpm’s are surging at idle. 650-1400 then somewhere in between. Rev engine and it would have a very noticeable miss. Thought maybe a vacuum leak and of course the new manifold has a recessed square plug that I can’t get out to hook a gauge up to to test for that. I decided to to look at my carb gaskets which are the quadrings and replaced them. Same results. I noticed the carb wasn’t giving equal amounts of gas on both sides and the air idle screws made no difference. I said the hell with it and replaced it. It’s an Edelbrock 1410. Installed seemed to run good and went to adjust the timing but no marks on damper, just a line for TDC. I did verify that it is TDC. Installed some timing tape to the damper and did the whole base timing procedure by mercruiser and it seemed to be perfect. Rev the boat to higher Rpm’s with no missing or hesitation. Rapped things up and was going to put it in the water the following day to test under load. I keep this on a trailer in my yard. Went out to it the following day cranked it and it started to act up again. Pulling my hair out. Anyone know an easy way to get that plug out of the manifold? No trusted mechanics close by otherwise I wouldn’t be wasting my time on this. Any help appreciated.