Fit to screen issues.

When I design a part with configurations that include a solid body I have issues with the fit screen working. if I design a engine head with a intake and an exhaust. I create the head and start by routing the intake with a spline, but when I work the spline for the exhaust manifold using a spline I try to make configurations that it does not show the exhaust and when I go to fit to screen, there is something attached to it and the head and intake manifold are displayed on the far left with plenty of room for the exhaust manifold to show up. even though I have the exhaust manifold suppressed. I have tied the exhaust to the head and to the origin resulting in the same problem. there seem to be several other glitches and I'm told it could be my computer or even the video card. but this particular issue seems to be the hardest to get around.