Hi I am having trouble with a 1980ish 7.5hp johnson. The motor runs fine in gear with the cover off. With the cover on the motor runs fine at idle but with not come up to speed in gear and it seems to be missing. In neutral it seems to rev up normal. It doesn't appear like the cover is pinching a gas line or causing problems with the throttle cable. The cover is fiberglass so I don't think a wire would be shorting out. Any ideas?