RebeccaBurg
Cadet
- Joined
- Nov 26, 2011
- Messages
- 24
Hello! Student mechanic seeks experienced help
I'm trying to diagnose a friend's nearly brand new 8hp Merc on a boat that was flipped upside-down in a storm in saltwater. (People okay, but waterlogged motor isn't) The engine was treated and flushed- crankcase, holes, valve train, intake manifold. Carb thoroughly cleaned out 3X, fuel flow great. Compression 110 both holes. spark both holes. all electrical connections appear undamaged and clean. Valve lash good & no oddities like damaged lobes on camshaft. Oil repeatedly changed/flushed.
Motor starts on first pull, idles smooth and nicely goes into gear. no smoke. BUT- as it's throttled higher it starts acting like a misfire: rough, jerky & feels like is running on one cyl. Still no smoking, just rough as heck. This happens whether or not it's in gear. It happens exactly when exhaust starts to bubble out of prop. Here's where my inexperience with 4-strokes really comes in.
Is it possible that seawater and the excessive oils used to flush engine are trapped in the block's exhaust passages? Too much backpressure cause this? I would think passages would be blown out, but am not sure. Is it worth the time to pull the powerhead to peek in there? Maybe hidden water still rolling about in carb midrange circuit even after three cleanings?
It feels like bad timing (but I think that's fixed on these motors) or mis-timed electrical system despite having spark...would the saltwater soaking damage such new and mostly sealed components? Flywheel magnets seem okay. I'm throwing this puzzle out here, & meanwhile will be looking up the specs & will make time for better testing of ignition system. I'm stumped and it's like chasing a ghost though this thing.
I'm trying to diagnose a friend's nearly brand new 8hp Merc on a boat that was flipped upside-down in a storm in saltwater. (People okay, but waterlogged motor isn't) The engine was treated and flushed- crankcase, holes, valve train, intake manifold. Carb thoroughly cleaned out 3X, fuel flow great. Compression 110 both holes. spark both holes. all electrical connections appear undamaged and clean. Valve lash good & no oddities like damaged lobes on camshaft. Oil repeatedly changed/flushed.
Motor starts on first pull, idles smooth and nicely goes into gear. no smoke. BUT- as it's throttled higher it starts acting like a misfire: rough, jerky & feels like is running on one cyl. Still no smoking, just rough as heck. This happens whether or not it's in gear. It happens exactly when exhaust starts to bubble out of prop. Here's where my inexperience with 4-strokes really comes in.
Is it possible that seawater and the excessive oils used to flush engine are trapped in the block's exhaust passages? Too much backpressure cause this? I would think passages would be blown out, but am not sure. Is it worth the time to pull the powerhead to peek in there? Maybe hidden water still rolling about in carb midrange circuit even after three cleanings?
It feels like bad timing (but I think that's fixed on these motors) or mis-timed electrical system despite having spark...would the saltwater soaking damage such new and mostly sealed components? Flywheel magnets seem okay. I'm throwing this puzzle out here, & meanwhile will be looking up the specs & will make time for better testing of ignition system. I'm stumped and it's like chasing a ghost though this thing.
