Engine: Mercruiser 470 (MCM470), s/n 5892137
This engine starts fine and runs great when first started. The WOT RPM's are 3800-4200 and it hits 4000 at WOT, about 35 mph and performs great. After I run it for about 15-20 minutes, if i come down to idle speed and then try to go back to WOT, the engine wont go over 2500 or sometimes 3000 RPMs, and the boat won't plane out. If I shut off the engine it may take a few cranks to start it. If I let it sit for 30-45 minutes, it will start up and most of the time get back to full WOT. Sometimes it doesn't. Sometimes it will get back up to full WOT but then die back to 2500 or 3000 again. When it does that, sometimes if I back the throttle down to where 2500 or 3000 RPM should be, and then try to open it all the way up, it will go back to 4000, and then of course other times it doesn't.
I changed the spark plugs and the engine overall sounded better but the problem still happens.
I don't have a water separating filter in the line. I'm going to put that in tomorrow. I was also planning on taking the hose clamps off the fuel tank and checking to see if the screens are 'gummed up' and clean them if they are.
Fuel sat in the tank for 6 months, but it wasn't much, and I've put in at least 15 gallons so far from the pump (40 gallon tank).
I was also going to put some Seafoam in the oil and squirt some into the throttle body while the engine was idling on the muffs.
What else should I be looking at? I've looked at some other posts, but most of them look like their problems are happening constantly, not apparently randomly like mine is. I don't think it's starving for gas... I mean it runs perfectly fine at first. I'd think if there was air in the line or the line were clogged it would never get all the way up to 4000.
This engine starts fine and runs great when first started. The WOT RPM's are 3800-4200 and it hits 4000 at WOT, about 35 mph and performs great. After I run it for about 15-20 minutes, if i come down to idle speed and then try to go back to WOT, the engine wont go over 2500 or sometimes 3000 RPMs, and the boat won't plane out. If I shut off the engine it may take a few cranks to start it. If I let it sit for 30-45 minutes, it will start up and most of the time get back to full WOT. Sometimes it doesn't. Sometimes it will get back up to full WOT but then die back to 2500 or 3000 again. When it does that, sometimes if I back the throttle down to where 2500 or 3000 RPM should be, and then try to open it all the way up, it will go back to 4000, and then of course other times it doesn't.
I changed the spark plugs and the engine overall sounded better but the problem still happens.
I don't have a water separating filter in the line. I'm going to put that in tomorrow. I was also planning on taking the hose clamps off the fuel tank and checking to see if the screens are 'gummed up' and clean them if they are.
Fuel sat in the tank for 6 months, but it wasn't much, and I've put in at least 15 gallons so far from the pump (40 gallon tank).
I was also going to put some Seafoam in the oil and squirt some into the throttle body while the engine was idling on the muffs.
What else should I be looking at? I've looked at some other posts, but most of them look like their problems are happening constantly, not apparently randomly like mine is. I don't think it's starving for gas... I mean it runs perfectly fine at first. I'd think if there was air in the line or the line were clogged it would never get all the way up to 4000.
