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holdover · 12-30-2020, 12:24 PM

OK, back to the basics. 1-2-3 cylinders are firing as they should. The valves for # 4 are moving and there is compression. There is spark at #4. If 1-3 are firing as they should to me that eliminates the carb, the coil, the points. after all why would it work for those cylinders and not for # 4. A test for leak at the intake at #4 shows no result. That leaves a few items; the head gasket at # 4 would be one thing, but it has compression, so that eliminates that, a clogged intake runner to # 4 as mentioned is possible, critters build nests in strange places. The odd part is that there is no wetness from fuel shown on the #4 spark plug, why, the clogged intake runner is suspect? A thought to me is compression is a result of the piston moving up and down in the cylinder with the valves opening and closing at the proper time as defined by the action of the camshaft, that action creates a vacuum that draws in the fuel, yet there is no fuel entering the cylinder the plug is bone dry. Could the cam grind on # 4 be wrong, so as the crank is turning the cycle is wrong and not creating a vacuum? If it was me before I tore anything apart I would make an adapter where I could use a vacuum gauge to see if Vacuum is created at the #4 spark plug hole while the engine is turning over. This sure is one I would like to know the answer to.

12-30-2020, 12:24 PM	#37
holdover Senior Member Join Date: May 2011 Location: SW Virginia near the Blue ridge Parkway Posts: 674	Re: Troubleshooting advice OK, back to the basics. 1-2-3 cylinders are firing as they should. The valves for # 4 are moving and there is compression. There is spark at #4. If 1-3 are firing as they should to me that eliminates the carb, the coil, the points. after all why would it work for those cylinders and not for # 4. A test for leak at the intake at #4 shows no result. That leaves a few items; the head gasket at # 4 would be one thing, but it has compression, so that eliminates that, a clogged intake runner to # 4 as mentioned is possible, critters build nests in strange places. The odd part is that there is no wetness from fuel shown on the #4 spark plug, why, the clogged intake runner is suspect? A thought to me is compression is a result of the piston moving up and down in the cylinder with the valves opening and closing at the proper time as defined by the action of the camshaft, that action creates a vacuum that draws in the fuel, yet there is no fuel entering the cylinder the plug is bone dry. Could the cam grind on # 4 be wrong, so as the crank is turning the cycle is wrong and not creating a vacuum? If it was me before I tore anything apart I would make an adapter where I could use a vacuum gauge to see if Vacuum is created at the #4 spark plug hole while the engine is turning over. This sure is one I would like to know the answer to.