Marine Chevy 350 idles & revs fine, except under a load it bogs down. Compression? or something else?

Question

rebuilt the carb, put in new plugs & Sparkplug wires.Verified timing ok.

Would a loose battery connection cause this? Checked the filter and carb. Out of gear it will hit 4500 RPM in less than 2 secs.

Answer 1

The Chev 350 is a super engine and if you get it right can produce up to 370 hp but like all V'8s it is the HT electrics that can let it down. It is not easy to tell if it is firing on all 8 by just listening to it. Check very thoroughly each lead to each plug and check each plug. Take each plug out in turn and run the engine and see if it makes any difference on any one plug Run it up in the dark or as dim as you can get it and watch for arcing out on any of the leads. I will bet you a £ odds on that is where the trouble lies. I assume you have not touched the valve timing

Answer 2

Check the drive train-with the engine out of gear (stopped)can you turn the shaft coupling by hand? If not perhaps the grease in the stern tube has solidified or it is over tightened-if it is a stern drive try turning the prop by hand (engine out of gear and stopped) if there is excessive resistance the problem is in the leg.

Answer 3

Its certainley not compression related as the lower end of the rev range is more affected than the top end if an engine has low comp.

Answer 4

Since the timing is ok then I would do a compression test,also check the out drive.

Answer 5

check and see when the fuel filter has been changed on it,those get a lot dirtier a lot faster than one on a car,and that will make them run like this,we had one with a 305 in it and it ran pretty good,bad on gas but it would run good,but i had to replace the filter about twice a year on it,to get it to run right ,good luck hope this helps.

Answer 6

First answer is good. Did you adjust the float properly when rebuilding the carb? Jets are clear?