87 cylinder on 90 bottom end CR250 PROBLEM

1987 cr250 cylinder:

http://www.bikebandit.com/houseofmotorcycles/1987-honda-cr250r/o/m11892#sch612762

1990 cr250 cylinder:

http://www.bikebandit.com/houseofmotorcycles/1990-honda-cr250r/o/m11897#sch414463

The only real difference between these (besides powervalves) is a port hole under neath the intake side. This port hole is present on the 87 cylinder and not the 90. The base gasket is the same between these so it led me to believe I could use it.

The problem is my radiators are being pressurized really bad and theres a lot of steam going on. My motor was idling perfect after the short warm up on first start-up after the rebuild. But it was getting too hot and theres lots of coolant coming from overflow and steam from around the right radiator.

Is this bad seals down in there or is it because of the extra port hole on the 87 cylinder?

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