The 1947 - Present Chevrolet & GMC Truck Message Board Network - View Single Post - Truck won't start right up and backfires like crazy!

cleszkie · 11-22-2011, 08:42 PM

If you think all of the plug wires are correctly routed, then I'd say you are 180 degrees off from TDC. Being a 4-stroke engine, the piston will be located at the top of its bore two times in a combustion cycle. The first time, both intake and exhaust valves are closed during combustion. This is TDC. The second time the intake valve is closed and the exhuast is open during exhausting. This is not TDC, and this is probably where you are at. Rotate the crankshaft until you are at what you originally thought was TDC. Remove the dizzy. Rotate the crankshaft one revolution until the timing mark shows TDC again. Install dizzy. Set 10 -12 degrees advance with vacuum advance disconnected. Reconnect vacuum advance. Should run now.

11-22-2011, 08:42 PM	#15
cleszkie Registered User Join Date: Feb 2003 Location: Santa Ana, CA Posts: 2,191	Re: Truck won't start right up and backfires like crazy! If you think all of the plug wires are correctly routed, then I'd say you are 180 degrees off from TDC. Being a 4-stroke engine, the piston will be located at the top of its bore two times in a combustion cycle. The first time, both intake and exhaust valves are closed during combustion. This is TDC. The second time the intake valve is closed and the exhuast is open during exhausting. This is not TDC, and this is probably where you are at. Rotate the crankshaft until you are at what you originally thought was TDC. Remove the dizzy. Rotate the crankshaft one revolution until the timing mark shows TDC again. Install dizzy. Set 10 -12 degrees advance with vacuum advance disconnected. Reconnect vacuum advance. Should run now.