misfire under load

["Matt Jacquet" <matt@vander-bend.com>]

 Hi All,

Been working on the white 68 (stock) R16 over the last few days and once
again stuck.
Car idles great, carbs sync'd up very nice and air fuel is also good.

Problem:

Pulls out of the garage and rev's up to about 3500 rpm's
after shifting into 2nd rev's up to 3k and then starts to run on 2
cylinders. Some times I can nurse it threw but sometimes not
Advance is hooked up and is timed to 16 deg TDC

TIA for any help!! Be nice to drive the car!!
Matt