RPM lagging

[briancarlin2006]

I laid up my boat last fall after changing the oil, applying a little Mystery oil to the cylinders and adding antifreeze to the raw water cooling system as I've done for years. The engine had run great all season. Upon start up on 17April2015, the engine started right up but lacks any power and fails to come up to speed. I did a compression test and all cylinders are 100 psi. All plugs look fine. The carburetor has a loud roar to it that it didn't have last fall upon advancing the throttle but fails to increase much in rpm. I'd did notice fuel "spitting" from the carburetor when the engines rev's the little bit it does. I did take off the valve cover and all valves appear to go up and down fine. I have not checked valve clearances yet. Any ideas? *** Upon looking further, I think the valves are hanging up a little as they don't immediately drop down to the tappets as they should. I've added some Marvels Mystery oil to each cylinder and turned the engine over to distribute the fluid. After letting it soak for a few days I'll try a restart. Thank you for all your suggestions. I'll keep you posted as to the progress or lack there of.... The engine is a short block rebuild from Moyer two years ago.

[Mo]

HI and welcome aboard.
Compression numbers are good. Check for spark on all 4 cylinders. Start and remove plug wires one by one and see if there is a change. Also double check that wires are in correct positions / firing order. That takes a few seconds to do and if nothing found there turn to the fuel. Ensure all fuel valves are open and check choke function. If anyone has been working on filters etc, check for air leaks. Other possibilities are condensation/water in fuel but I would expect stalling and rough idle with water...sputtering. Another issue could be main jet plugged on the carb.

[Marian Claire]

Another welcome.
Can you expound on " fuel "spitting" from the carb..." Is the flame arrestor clean? Any chance of a critter induced exhaust system plug? The plug wire test, suggested by Mo, may help with that question. Was the boat in or out of the water for the winter? Fouled prop??

Dan S/V Marian Claire

[hanleyclifford]

I would put my chips on the "plugged main jet".