aj1988

Sorry to ask, but it has been at least 10 years since I have tried to get a small block going so I need some help.

I gave my son a 72 that has a newly rebuilt engine. At idle it runs as smooth as a baby's .... When you try to drive it, it has a really bad miss. Since he is in Tx. and I am in Mo. it is hard for me to really help him. I think it is ignition related, but not totally sure. Told him to get new points, rotor, cap, and coil. It has new wires and the plugs look OK.

Is it possible that he has the valves to tight?

Any assist would be greatly appreciated.

Thanks. Oh yeah, the reason I gave him the car was as a wedding gift. I was umemployed at the time and the wifes folks gave them a trip to Hawaii for a wedding gift. Besides, he was going to get it eventually. Just a little earlier than planned.

tippi58

If smooth at idle and runs rough when on the road, sounds more timing, gas or a vacum problem.

If I were to pick one that would be more likely I would go for the gas problem.

Its getting enough gas at idle but when it wants more its restricted.

Have him check the fuel pressure with a guage.

:cool: :cool: :cool:

vettfixr

I think you're giving him good advice. He should change out the plugs, wires and points. If he can go for a few extra bucks change the points over to a Pertronix unit and he won't have to worry about them again. He should make sure the cap and rotor are good and that the plug wires are separated from each other and held in plce correctly. If the car surges at low engine speeds while driving he may have the timing too far advanced or the ignition curve may be coming in too quick. If he's not familiar with advance curves he can look around for a shop that can check the distributor for him. If he can handle a timing light he should get a timing tape in the right size for his balancer and check the advance. Without the vacuum advance connected he should have a max or 34 to 36 degrees advance at between 2500 to 3000 rpm. If the timing continues to climb after 3000 rpm then the springs in the distributor are too stiff. He can get a set of distributor springs at most auto stores (Mr. Gasket sells them) and change to lighter springs until he gets the correct advance all in by 3000 rpm. If he has more than this he should back up the initial timing by the amount that he is over. If he doesn't have 34 to 36 degrees he should advance the initial timing so that he has it. Once he checks this he should momentarily connect the vacuum to a full vacuum source to see if the timing jumps. If it does then his vacuum advance is working OK. The vacuum advance should be connected to a timed vacuum port on the carb so that at idle there is no advance. With the vacuum advance connected he should check the max advance again. The initial + mechanical + vacuum should give him no more than around 52 degrees advance at 3000 rpm. Sometimes the vacuum canister has more advance and will cause the engine to exceed the 52 degree max. He can change out the vacuum canister to one that gives less advance. Go to corvettefaq and print out Lars paper on this. He has all the part numbers listed and a better description of what I just told you. If all of this fails he may have a fuel delivery problem. The carb may be faulty causing a lean misfire under load or it may just not be metering the gas correctly. If he knows someone that has a carb he can borrow he can eliminate this question by swapping them out temporarily.