Thread: NO combustion in 2 of 8 cylinders

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Have an old ski boat with a chevy small block V8 engine in it. I currently have great compression in all 8 cylinders (115-135) but am not getting ignition in 1 and 3. Holley carb with the two barrels in the back and one combined on the front. Kind of a rookie but checked wiring order, spark for each and even pulled the valve cover off to see if there was a cracked spring or bent rod but everything is fine from that point. New plugs all around and after one day on the lake at 8 miles an hour the functional cylinders had some blackness but the 1 and 3 plug looked like they were fresh out the box, shiny and new. She ran great all last season but after being stored for the winter she has been a no go so far. Did not fade to this. More all of a sudden over the winter.

It seems as if I am not getting fuel to just those two cylinders. Any ideas?

holley carb with 2 barrels in the back and one combined in the front???? are you talking about a choke tower that might look to be one barrel or are you talking about a holley 3 barrel carb???

What ignition system are you using?.Shiny can mean a intake coolant leak on one and three that wouldn't show on a compression test.

With a carbureted engine the only way you cannot be getting fuel to only two cylinders is to have something keeping those two intake valves from opening (cam lobes flat, pushrods bent/broken, rocker arms damaged, valve springs, valves) unless you have a couple of dead mice in the intake, and you should smell that by now . You say you checked for spark at each cylinder - how did you do that, and was the spark a good, hot blue-white spark at each one? How about switching plugs, using two that you know were firing in other cylinders and see of your miss follows the two plugs you had in 1 & 3? Could be as simple as bad plugs out of the box? Next I would look at the distributor - what type ignition are you running?

How have you determined you have no spark to those two cylinders? My first thoughts are that you are getting water in there from a bad exhaust manifold or head gasket.

Don

I am not sure how you would check a coolant leak on a boat engine with it not having a rad.Seems you couldn't pressure test it.

There are usually tell tale signs, like the plugs being clean or rusty in those cylinders, or, if you pull the exhaust manifold off, you will see rust tracking in the head exhaust port. Sometimes you just see small beads of water inside the insulator portion of the sparkplug.

I've seen them where the leak was so small the boat ran pretty normally but just had an occasional miss. As the leak gets worse it can even get to the point where enough water comes in to hydrolock that cylinder or bank of cylinders, and if it sits too long (like even a few days) the piston rusts firmly to the cylinder walls.

I rebuilt a marine engine for a buddy one time, after it had sat for only a week since last running, and we had to drive the pistons out with a block of wood and a sledge hammer.

Don