QuestionJust required a 1940 Packard model 120. Engine was running poorly(poor throttle responce) bad compression in #8 (30psi)
Removed intake and exhaust mahifolds to replace all gaskets and adjust tappets. This restored the lost compression in #8 and actually seemed to even up all the cylinders as far as compression (all 8 around 120psi). The engine will not idle properly once started and running. At fast idle with the choke partially closed its very smooth. Once it heats up the idle is poor and the idle adjustment screws seem to have no effect. The throttle responce even off a poor idle is instant. The engine was spitting out the carb. before the tappet adjustment. All the plugs are new, as well as the points. The plugs all appear the same in appearance; no oil fouling in fact they look perfect. The carb. is a Stromberg EE-16 which may have been rebuilt. The plug wires, cap and rotor are new. The heat riser in the exhaust is free with the bi-metallic spring in tact. Thank you for your time.
AnswerThis sounds very much like a vacuum leak to me - so let's check that out first.
Take a piece of cardboard, and with the engine idling slowly (and poorly), with the air cleaner removed, slowwwwwly slide the cardboard across the top of the carburetor, so as to reduce the amount of air getting down into it. If at ANY POINT in this process, the idle improves, we know the mixture is too lean. There are two possible reasons for this: 1. there is a vacuum leak in the intake system somewhere, or 2. the idle mixture circuits are plugged with crud.
Investigate for a vacuum leak by verifying that the vacuum connections to the intake manifold are all capped off (temporarily, just to make sure the problem isn't in the fuel pump or wiper system) and then take a can of WD-40 and spray short puffs at all the mating surfaces between the intake manifold and the carburetor and also around the intake ports on the side of the block. If at any time, you notice an effect on the idle, you've found the leak. if you cannot find anything that way, disconnect the vacuum line to the distributor at the distributor end, and cap that off - just in case there is a bad vacuum diaphragm in the distributor advance mechanism, and see if that makes any difference (it shouldn't, because that is ported vacuum, not intake vacuum, but if there is a problem in the carburetor, it might also bother the idle.
If you can't find anything that way, go to suspicion #2: Turn the engine off, then take both idle mixture screws all the way out, and with a can of spray carburetor cleaner (Gunk is a good brand), stick the nozzle all the way into the screw sockets and give a healthy squirt of the solvent in there, then follow that up with a burst of air from a compressor (set it to around 20 PSI) to dry things out, then put the screws back in, set them to about 2 turns out, and try the idle again. If it still idles poorly, I think it is probably going to have to go to someone with an engine analyser to see what is going on. It is possilble there is still a problem in the carburetor (the Strombergs are somewhat troublesome - and lots of folks have converted to the Carter WDO), but of course a skilled carb guy could track down the problem. Mainly, if the rebuilder did his work right, perhaps some fine particles of crud have made their way into the idle passages.
Let me know how this works out, please.
Dick
