VCCA Home Forums TECHNICAL - 1945 AND NEWER 1946-1948 Engine 'Miss"

I am a new forum member and I thought I would start a new post to see if anyone can help me with my 215 CI 'miss'. The car is a 48 Fleetline, all stock, no modifications. I have run a compression check and each cylinder is compression testing at 90-100, timing was checked and seems to be right on. Removing the plugs to do the compression check showed them to be light tan in color at the electrode. BTW, I had installed a new cap, rotor, wires, and plugs within the last 5 - 6 months. The engine miss was apparent before I changed out all of those parts. I adjusted the carburetor the best I could as well. When at idle, it will slightly miss, or appear to "skip". When I drive the car and I am going down a long hill, in gear, and under load, the car seems to want to backfire, and makes a kind of muffled burping sound, as if it's trying to belch. That's the best way I can describe the problem. I have checked for exhaust leaks and there aren't any and I have checked to see if there is a vacuum leak, which there is not. Could my carb be the reason why it's acting this way? If so, is it better to rebuild my unit (Carter W-1) or buy one already rebuilt? Any help is appreciated.

Thanks,

Tony

If it has an original type Carter W-1 carburetor it could have dirt in the low speed jet.
Remove the air cleaner. Put #3 spark plug wire on #4 cyl and #4 wire on #3 cylinder. Start the engine and briefly floor it a few times. It will back-fire thru the carburetor and blow the dirt (if there is any) out of the low speed jet.
The "normal" compression for that engine should run from 110 to 120 pounds.
With the 10 pound difference you have the low cylinder(s) and high cylinders could be the rough idle problem.

Chevgene,

Thanks. I'll try swapping out the plug wires as you suggested. I may take a second look at doing the compression check too. I only let the car crank 5 - 6 times on each cylinder. BTW, only 1 of the cylinders was at 100lb, the other 5 were at 90lb. I'll post my results on what I discover.

Thanks again,

Tony

Gene,

Looks like your advice did the trick. Car now idles a little smoother then before and the slight skip or miss has all but disappeared. I haven't taken it out on the road yet, but I will after I finish up doing some detailing. See my other post about intake/exhaust manifolds.

Thanks,

Tony

Did you do a dry then wet compression test? The wet test will help identify a valve problem as opposed to a ring problem. Also using a vacumn gage will help identify engine problems.

Glyn,

No I haven't performed a second compression test yet. I'll have to do that when I get the manifolds painted and put back onto the car. Of course, I found about 4 - 5 other 'while I'm at it' projects when I took the manifolds off, so it may be a couple of weeks before I can get it ready. Question: What is a 'wet' compression test? Also, how would I be able to use a vacuum gauge to identify other engine issues on the '48?

Thanks,

Tony

I think a WET compression test is to squirt a little oil into the cylinder to see if the compression increases and that would say you have blow by on the rings. As for the vacuum gauge I think you would watch for no large fluctuation in the reading if you have that it would indicate a bad cylinder if this is not correct could someone set us both straight.

Andy,
You got the wet test right. Do a dry test on a cylinder, record the max pressure after 3+ compression strokes (all spark plugs removed), squirt in the oil and record the max pressure again. Comparing the dry and wet gives an good indication of the condition of the rings.

The vacuum gauge is extremely valuable tool. Fluctuation indicates several possible problems. Low vacuum indicates one or more of many problems. It is best to look up the discussion of how to use a vacuum gauge in a repair manual like Motors, Chiltons, Audels, etc. Modern manual is okay as the technique is the same for all carbureted engines. Later GM or Chevy manuals also contain the procedure.

Andy29, Chipper,

Thanks for clarifying what a 'wet' compression test is. Once I finish the current project, I'll try that and post the results. Also, when doing any vacuum testing, where should I connect the vacuum gauge to? All the vacuum lines are steel with the exception of the rubber vacuum line that is running from the intake to the wiper motor. Should I just plug my vacuum gauge into the intake port? Thanks for all your assistance!

Tony

Any port that goes directly into the intake manifold will be okay. Some around the carburetor base are ported and the vacuum depends on the position of the throttle plate.

Just an update....

I had taken apart the exhaust/intake manifolds, and the carb, and replaced the header pipe a couple of months ago. I cleaned, painted, detailed all those parts and replaced the header pipe and finally took the car for a spin yesterday for the first time in quite a while. Lo and behold, the 'miss' or 'skip' I was hearing is no longer present. There does appear to be a minor exhaust leak downstream somewhere that I'll locate later. I have not done the the dry/wet compression test yet, but will later. I don't think that I have a stuck valve at this point. It now appears that I must have had an exhaust or vacuum leak somewhere in the system. BTW, the header pipe was really rusted and I was able to create a hole in the header pipe with a simple poke of a screwdriver. Anyways, happy days for me. Nice day yesterday for a cruise, 50 - 60 degrees out and clear. Car was running nice.

All that was needed was for you to take a little drive to get her heart pumping. Enjoy the ride, Thats what it is all about !

Gene, I have the same problem with my 53-235, chev,,, I replaced just about everything including the carburetor and all the vacuum lines, can't seem to lose the miss,,

a question,, when you do the wet or dry vacuum test ,, do you not leave all plugs in during the test except the testing cylinder ?? I think you meant to remove all plugs, oil the cylinders and then replace all plugs ?? Or did I learn sumtin backwards ?