so i just dropped a used motor into the 7.

adjusted the throttle screw to have it stay around 1000 rpm and i get 17psi vac.

but if i let the screw out a bit, as the rpm drops to about 600-700.. i only get 10psi vac. i haven't gotten a chance to do a compression test.. but should i fear bad compression?

thanks

 

There's far too many things that affect idle vacuum. If you're unsure of compression, do a compression test and get a good answer.

Dale

 

Pending there are no other vac leaks, get the car warm and let it idle at 850. Then see what the vac is. This of coarse is for a stock ported motor but if you are seeing 15 inHg or more than it should be good. If there is significant porting the vac will be less. REALLY if you are worried about this you should just compression test the motor.

Edit** Dale beat me to it.. He is one of the best to listen to. Lots of variables if the vac is low. Just do a comp test which will be definitive.

 

got it. just bought a compression tester... any idea how to do it by yourself?

 

put the gauge in a spot where you can see it from the drivers door and hang your head out while holding the throttle down and cranking the engine over. be sure to pull the EGI fuse out first! to make it a little easier you can put something on the throttle pedal to hold it all the way to the floor and you can use your right foot to hold the clutch in while cranking to get yourself out the door a little better for a good view of the gauge. the battery should have a full charge as well and remove both leading plugs while doing the test to get cranking RPMs up as high as possible(having one plug in will put more drag on the starter).