Need help tuning a 273.

My .$.02

All extra vacuum lines on the carb should be plugged. If you have two open for the distributor, either put a Y on the distributer line to both vacuum openings, or put a plug on one of them. I know my 273 has a Y prior to going into the 2 vacuum lines on my carb.

Be sure distributor line is disconnected from distributor and plugged before timing.

Normal timing in on mine is 12-14 BTDC, even though the manual says lower.

Set Timing at 800rpm or less. Less is better as anything above 900 and the advance weights will start to change it timing automatically.