hey folks, need some input 5.7 omc engine runs fine no load, checked timing, advance timing ok, compression reads 165 to 185 in cylinders, has new carb, fuel pump filters, pulled fule lines in tank check valve fine vent valve clear, engine just wont go above 2600 rpm when under load, carb opens secondaries
open carb growls at you but engine wont increase rpm, feels like boat is overloaded or engine is underpowered like bad rings but no blowby noi oil consumption, pulled valve covers to inspect valve movement all looks fine no indication of worn camshaft, cam timing perfect, no slack in chain, vacume guage reads 18 inches steady at idle , even in gear vacume drops to about 14 inches with steady needle, i was suspecting exhaust restriction but do not get a positive/pressure reading on vacume guage whenhis happens, note vacume guage is run into port on back of intake manifold. ignition system was replaced with breakerless system but i dont know if this could be a problem even whenin drive i took a timing reading and had 18 degrees of advance at 2800 rpm but engine still wont go any faster, i will pull exhaust manifolds and inspect flappers for restriction, any possibilities of bellows collapsing? we did change the prop from 17 pitch to 15 pitch but no change, did notice when trying to diagnose problem if you trim outdrive up seems to make worse rpms seem to drop a few hundred rpms, any suggestions, thank you rodb267.
open carb growls at you but engine wont increase rpm, feels like boat is overloaded or engine is underpowered like bad rings but no blowby noi oil consumption, pulled valve covers to inspect valve movement all looks fine no indication of worn camshaft, cam timing perfect, no slack in chain, vacume guage reads 18 inches steady at idle , even in gear vacume drops to about 14 inches with steady needle, i was suspecting exhaust restriction but do not get a positive/pressure reading on vacume guage whenhis happens, note vacume guage is run into port on back of intake manifold. ignition system was replaced with breakerless system but i dont know if this could be a problem even whenin drive i took a timing reading and had 18 degrees of advance at 2800 rpm but engine still wont go any faster, i will pull exhaust manifolds and inspect flappers for restriction, any possibilities of bellows collapsing? we did change the prop from 17 pitch to 15 pitch but no change, did notice when trying to diagnose problem if you trim outdrive up seems to make worse rpms seem to drop a few hundred rpms, any suggestions, thank you rodb267.
