The 1947 - Present Chevrolet & GMC Truck Message Board Network - View Single Post - Knock after a simple carb swap

f.monroe · 09-17-2020, 10:11 PM

You could have a piece of carbon lodged on top of a piston. Will knock like crazy. Should be able to feel it if you turn the engine by hand . There are engine cleaners for this. I think GM use to have a Top Engine cleaner to run through one. I watched an older mechanic fix a 4.0 liter jeep with a can of water that was knocking. I've also heard of running trans fluid through the carb to burn the carbon off. Hope its something on a piston rather than a bearing.

09-17-2020, 10:11 PM	#8
f.monroe Senior Member Join Date: May 2004 Location: Caldwell,Tx. Posts: 3,648	Re: Knock after a simple carb swap - Thoughts? You could have a piece of carbon lodged on top of a piston. Will knock like crazy. Should be able to feel it if you turn the engine by hand . There are engine cleaners for this. I think GM use to have a Top Engine cleaner to run through one. I watched an older mechanic fix a 4.0 liter jeep with a can of water that was knocking. I've also heard of running trans fluid through the carb to burn the carbon off. Hope its something on a piston rather than a bearing. __________________ Born and proudly residing in a Red State !