heres a thought i know my cam is way to big my carb way to small and my preformer intake to restrictive for my heads (ported and polished) and my car idles like crap when it does made small adjustments to carb and got it as best as i can. (found out recently the parts arent meshing) so my thoughts on this are that one ore more parts not meeting the requirements you need. and the 750 you borrowed may not be adjusted to your engines need hence the problem still there