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Old 06-15-2018, 01:49 PM   #1
saintjoelarry
Junior Member
 
Join Date: Nov 2011
Location: Grand Rapids, MI
Posts: 25
Default Help - My A is barely running

I've been struggling with my A for some time now, and I'm not stumped.

My 31 Roadster ran fine the first 2 years after I purchased it. Then out of the blue one time while driving, it started loosing power, and my speed dropped. Then dropped further, until I limped home the last couple miles at no more than 20 MPH.

Here are the symptoms, followed by what I've done to date.

Sypmtoms:
- Very little power
- Runs fine at idle, when I accelerate, it pops/backfires out of the carburetor
- Also, while running even at idle, there is a loud whining noise. I cannot pinpoint its location. Is pretty clear echoing out of the exhaust pipe, but at the engine, I cannot pinpoint the source.

What I've Done
- Ignition? - Started with the easiest things first, right on the side of the road that day. I've now timed the distributor probably 20 times since this whole thing started, with no change. I've tried 3 different condensors, 3 different coils, and 2 different coil wires. No change.
- Checked for Burned Valve or Hung Up Valve - First, I ran compression check on all cylinders. They were all 60 to 62 psi compression, which seems to be within range.
- Check Valve Timing - Although it seems unlikely that valve timing would change on a model A (giving the steel timing gears - more on that later). I checked that both valves of each cylinder are closed when the piston is at TDC on compression stroke. Using a flashlight, I can see the valves are closed.
- "Static" Compression Check - not sure what else to call this test, but with each piston at TDC on compression stroke (both valves closed), I attached my compression test hose, then set my air compressor hose pressure very low at 20 psi (low enough so that it didn't push the cylinder down), attached the hose to my compression hose, and listened for air movement. I heard no air coming from the carburetor or out of the exhaust. There is some air flowing past the rings into the oil pan (heard clearly through oil fill tube). Although that's not great, it certainly is not unusual in my experience for a Model A to have ring blow-by. Also, this should not cause back fire through carburetor.
- Bad Head Gasket? - I thought maybe I had a bad head gasket between 2 cylinders. But, when I did the compression check, all spark plugs were out. If compressed air was escaping from one cylinder to the next, it would have shown essentially nothing on the compression gauge. Also, the static compression test would have had air leaking out of neighboring sparkplug hole.
- Bad Timing Gear? - As I also had a pretty decent oil pan leak, while I was stumped, I decided to go ahead and replace the pan gasket. While down there, I could clearly see the timing chain gears - so I watched the gears as a friend turned the engine over. The gears look great. No missing teath.


Now what? I'm stumped. Could a gaket between the exhaust and intake manifold have failed, causing exhaust gas to be pushed into the carburetor (thus the back firing)? Seems unlikely, but who knows.

Any help would be greatly appreciated!


Larry
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