My T (1925) normally runs very nice. But now I have the following: It runs maybe 5 Minutes, then it seems like it runs only on 3 cylinders.
I already changed the 4 plugs and the ignition coil (12V). I tried it now 7 times, I always come home, but only very slow and with a lot of jumping.
When I make contact with a screwdriver on the first plug, there is now reaction, when I do it on the other 3 plugs, it runs slower. I changed this first plug already 2 times. It don't happen when it runs on idle, it always happens in the second gear.
I think, I already had this 2 years ago, but then I didn't really find out the reason, suddenly it went away and I drove maybe 200Miles since then. Now it seems to be the same.
I also played around a bit with the carburetor (Rayfield), but there is no difference.
Any other ideas ?
Stuck valve-probably exhaust- on number 1 cylinder?
You mention a coil so I'm assuming a distributor. Perhaps a cracked cap or a carbon track in the cap? Certainly could be a sticking valve too as George mentioned. You'd hear noise at the muffler for an exhaust valve and at the carb for an intake valve. If your ign system checks out OK warm it up till it begins to miss and take a compression test. That'll tell quick enough if it's a valve hangin'.
By the way, you mention shorting the plugs. Assuming again you are getting a spark at #1 even though it doesn't affect the engine? If so it's probably not ignition.
Hi, thanks for your tips:
The cap of the distributor is very clean. I use a electronic ignition. I have a Texas-T-Parts distributor. It works good.
So maybe it's the valve ?
So maybe I will remove the head and check the pistons and will remove the valves of the front cylinder.
Last time, when it happened, it was about 30 degrees Celsius outside, now it's only about 5 degrees, and it feels like it would be the same.
But maybe you have other ideas?
Before you tear anything apart,i would do a compression check! Bud in Wheeler,Mi.
Compression check is what you need at this point. Fuel, ignition and timing are useless without compression. Doesn't have to be a high tech test, just plug the hole with your thumb and have a helper crank the engine. Compare the result with a cylinder that is functional, it should be hard to keep the hole plugged. If only one cylinder has low compression, a valve problem is most likely.
Make sure your battery is strong, the Pertronix needs a good battery any power loss will cause strange things to happen. I was driving one day and applied the brake, the engine quit, I pulled over and checked everything, it started right up, next stop the same thing happened, so have your battery checked for power not volts.
Check the valve springs and spring pins. I had a valve pin bend and the valve didn't operate properly. Look for a broken spring too.
First check compression. Should be somewhere between 45 and 50. If you have good compression on number 1, while the plug is out, turn over the engine with the plug out and laying on the head. Should see a spark at the spark plug. If not, you have an ignition problem.
Some ignition problems present themselves at high compression which occurs under acceleration. If the spark has a hard time jumping the gap in the spark plug it will find the shortest route to ground. This could be an insulation problem on the wire which would allow the spark to go to ground or it could be a carbon trace inside the distributor cap. Another possible cause would be worn bushing in the distributor causing the points not to open. A larger gap between the points might fix this type problem but the more permanent fix would be to re bush the distributor shaft.
Willi - You've obviously determined the bad cylinder to be #1, and the #1 cylinder seems to have the strongest tendency to foul the spark plug. I guess due to fuel distribution and the fact that air from the fan tends to cool the front section of the manifold which is closest to the fan. Even before doing a compression test, I would swap the #1 spark plug with one of the other spark plugs, and see if the dead cylinder follows that particular spark plug. Easy test, and you have to remove the spark plugs for a compression test anyway,...... FWIW,......harold
I already measured the compression, they are all OK.
I removed the valves now. everything looks OK.
But the cylinder head for 3 and 4 was very black but dry and the cylinder head 1 and 2 were totally wet from oil, because I was driving with only 2 cylinders for about 1 Kilometer.
Now I think, it's only the carburetor which is to fat.
I only have my Rayfield carburetor since some month and it dind't run perfect till now. I think, I have to make a smaler nozzle, because I never can make it lean enough to start the correct settings.
But thanks for your tips-
Geez Willi, all you had to do is what I posted earlier. Run it until it misses and take a comp test. It would have shown the condition of the rings & valves without pulling the head. If # 1 & 2 were wet inside the cyl head those plugs would have been wet too. It doesn't sound like the head needed to come off at all. Take your time and ask more questions before you tear anything else apart.
Maybe the inlet manifold leaks at #3 and #4, making the mixture to the rear cylinders too lean, then you compensated by opening the carb needle until the rear cylinders ran good - resulting in a much too rich mixture to #1 and #2. Since #1 runs the coolest, it'll be the one that fouls the spark plug first..
So, try again with new copper gaskets for the inlet manifold. It's easy to check for leaks with a can of wd40 at idle right after cold start when the exhaust manifold hasn't got too hot yet.