Rough idle and takeoff 250 inline

[68gmcdude]

[QUOTE=HO455;9346799]One of the best troubleshooting tools for this would be a quality vacuum guage. Old school mechanics used them regularly to direct themselves towards the problem. Every Chilton and Hayes repair manual has a section on how to use one.

After reading your initial post my first thought was that you had a burnt valve. At this point if you don't want to use a vacuum guage and you want to check your compression do a leak down test instead. Properly done a leak down test will tell you if you have a valve sealing problem, a ring sealing problem, a bad head gasket or cracked block.

I just ordered a leak down tester. Thanks for the links. Great info.

[RichardJ]

>>I just ordered a leak down tester.<<

Did you back that lifter away from the 2 extra turns and recheck the compression?

Please do that before buying a tester.
If you want to do the same thing a leak down tester will do without buying the tester. Put the piston on the cylinder to be tested, at TDC. Wrap a small rag around an air nozzle to seal it and blow air into the spark plug hole. Do remember there are two TDC for every piston.
If you have a broken ring, You will hear air coming out the oil fill hole on the valve cover.
If you have a bad Exhaust valve, you will hear air coming out the tail pipe.
If you have a bad Intake valve, you will hear air coming out through the carb.
If you have a bad head gasket, you may see air bubbles in the radiator.

A leak down tester will do the same thing except give you some numbers, which won't mean a damn thing anyway.

You do have a compressor for the leak down test? Sorry, just asking as I don't know.
Some guys don't, but I always use some means to lock the crank from turning for a leak down test. You put 100 psi on a piston and if it wants to go down. it will. The first time it happens, you may need to change your shorts.