The Stovebolt Site Forums The Shop Area Engine Shop Sticking Valve?

My truck (stock 1949 216) has been running funny. A while back I noticed a bit of a stumble at acceleration and occasional back fire. My exhaust is not good so it's hard to tell if it's throught the carb or exhaust. I've since replaced the cap, rotor, plugs, wires, points, condenser, fuel pump and filters, rebuilt the carb, set timeing and adjusted lifters. Compression is 120-120-119-120-119-120. I thought I'd fixed it (for about a week) but I'm getting the same simptoms. The thing is it comes and goes. It'll stumble, backfire, and run like crap one day and the next it'll run like a dream. Last night it was terrible, missing and backfireing. This was the first time it had a constant miss. I pulled each plug wire but got the same subtle miss on each cylinder so I don't think it's in the ignition. I fired it up this morning and drove it around and it ran great! Is this a sticking valve?

I use an inductive timing light to check my ignition. Each plug wire should have steady flashing with no skips as the engine runs. Also, have you checked that the vacuum advance is working? Distributor should physically turn when you rev the engine. I had a similar problem as you last year and ended up replacing the distributor. Runs great since then, fires right up even after sitting a couple days.

Concur w/Ed, 1st thought is a vacuum leak,possible at the dist vacuum adv unit, the line to it or at the manifold.

Plug the vacuum line fitting at the manifold and test.

Another test to try is while it's idling, remove the air cleaner and cup your hand over the carb in an attempt to cover it up. This will enrich the fuel/air mixture. If idle picks up you've got a vacuum leak, if it trys to stall out you may not.

Like Ed said with the vacuum line connected the whole dist should rotate when you increase rpm, make sure.

Good luck
Dave

I'd take the coil wire out of the coil and look at the end of it to make sure its ok. Also check to see if the coil has any oil leaking out of the center. I would suspect something ignition related.

My truck starts right up after setting for two days in this cold if I pull the choke out and I don't even have to give it gas. No problems there. Vacuum advance works right. I've checked for vacuum leaks, including plugging the vacuum line at the carb base, all is good. The miss at idle last night was steady, like a dead cylinder, but each plug wire I pulled had the same effect. I do have a replacement distributor that I need to rebuild. Cold weather coupled with no garage makes it slow going

So do you not think it's a sticking valve?

Don I replaced the coil wire and the old and new wires look fine. The coil is dry, it is the only thing I haven't replaced.

ah, you got the gremlins this week...

Water/ice in the gas?