EchoNovember
Petty Officer 1st Class
- Joined
- May 25, 2017
- Messages
- 315
As the title says, I have a 1985 Mercury 75. When I bought it was hard starting in the water, and would die at idle, even after running for a long time. It would do this in the water and on muffs. The carb bowls were leaking at the gaskets, so I ordered a gasket kit and in the mean time sprayed Seafoam into the carb throats and fired up the engine. I gave occasional sprays to make sure there was plenty in there, then shut it off and let it sit. Took the spark plugs out and sprayed what was probably a more than generous amount of Seafoam directly into the cylinders, put new plugs in (stripping out one and having to put in a helicoil to repair it) and let it sit. I fired it up after a day or two, and after the smokescreen faded the engine ran like it was new, on muffs.
Gasket kit arrived, so I took off the carbs, didn't touch any adjustment screws, sprayed out the carbs with carb/choke cleaner (forgot to spray out the chokes), put the new gaskets on without any sealant, just bare gaskets, and put it all back together. Pumped the bulb for what seemed like forever to refill the carb bowls, and tried to start it. It didn't want to run... It was late at night, so I gave up for the day. The next day sprayed a small amount of Seafoam down the throats, and went to start it. It fired up in a second. No kidding, one second. Fired up straight away, no fuss, ran like the day it left the factory floor. Full of pride, I couldn't wait to get it on the water.
Took it out to a lake a couple days ago all excited to have a smooth running engine, anxious to show off mah skillz. The water hates pride. My engine did not want to start. When it did, it died quickly at idle. I had to put it in neutral and turn up the throttle to get it started and keep it running. When I dropped it back down a little, not even down to idle. it died. It kept dying. It died the moment I rammed it into reverse trying to get away from the launch. It died when I did anything, until I had the throttle up in neutral and quickly brought it back to idle, then shoved it forward to get moving, then it ran fine. I could cruise all day, it had no issue once I was moving. As soon as I dropped it back to idle, it died.
I'm no expert on outboards, which is why I am on here asking for help, but (of course there was going to be a "but") it seems like the water pressure is preventing the exhaust from escaping properly, causing the engine to strain and quit at idle. Yet exhaust is coming out of the exhaust pressure relief ports, so that kind of pokes a hole in that one.
The only things I can think of at this point are:
Idle adjustment screw needs to be tweaked
The dirt cheap 2-stroke oil the PO gave me isn't burning properly, causing power issues
Something is clogged with the exhaust and exhaust pressure is too high, killing the engine
I have a family camping and fishing trip coming up in ten days, so I am under a time crunch to get this fixed. Any help is greatly appreciated.
16' 1985 Starcraft SS 160
91 Octane Ethanol-free (yes, actually ethanol free) non-oxy premium gas
Cheap Walmart 2 stroke oil, TC-W3, 50:1
Seafoam in gas, dosed per can instructions to avoid thinning the oil
New Champion spark plugs
Dielectric grease on the spark plug boots
Anti-seize on the spark plug threads
Spark plugs torqued to 20lbs per service manual
Fuel pump filter screen removed and cleaned, then put back in
No fuel leaks anywhere
Spark on all cylinders
Compression not checked
Carbs clean and looking new, no corrosion, trace varnish in bowls
Remote controls, cables, have not adjusted
Newer battery, fully charged
Old steel gas cans, but no sign of rust or corrosion that I've seen
Newer Attwood fuel line and bulb.
I think that is about everything I can think of.
Gasket kit arrived, so I took off the carbs, didn't touch any adjustment screws, sprayed out the carbs with carb/choke cleaner (forgot to spray out the chokes), put the new gaskets on without any sealant, just bare gaskets, and put it all back together. Pumped the bulb for what seemed like forever to refill the carb bowls, and tried to start it. It didn't want to run... It was late at night, so I gave up for the day. The next day sprayed a small amount of Seafoam down the throats, and went to start it. It fired up in a second. No kidding, one second. Fired up straight away, no fuss, ran like the day it left the factory floor. Full of pride, I couldn't wait to get it on the water.
Took it out to a lake a couple days ago all excited to have a smooth running engine, anxious to show off mah skillz. The water hates pride. My engine did not want to start. When it did, it died quickly at idle. I had to put it in neutral and turn up the throttle to get it started and keep it running. When I dropped it back down a little, not even down to idle. it died. It kept dying. It died the moment I rammed it into reverse trying to get away from the launch. It died when I did anything, until I had the throttle up in neutral and quickly brought it back to idle, then shoved it forward to get moving, then it ran fine. I could cruise all day, it had no issue once I was moving. As soon as I dropped it back to idle, it died.
I'm no expert on outboards, which is why I am on here asking for help, but (of course there was going to be a "but") it seems like the water pressure is preventing the exhaust from escaping properly, causing the engine to strain and quit at idle. Yet exhaust is coming out of the exhaust pressure relief ports, so that kind of pokes a hole in that one.
The only things I can think of at this point are:
Idle adjustment screw needs to be tweaked
The dirt cheap 2-stroke oil the PO gave me isn't burning properly, causing power issues
Something is clogged with the exhaust and exhaust pressure is too high, killing the engine
I have a family camping and fishing trip coming up in ten days, so I am under a time crunch to get this fixed. Any help is greatly appreciated.
16' 1985 Starcraft SS 160
91 Octane Ethanol-free (yes, actually ethanol free) non-oxy premium gas
Cheap Walmart 2 stroke oil, TC-W3, 50:1
Seafoam in gas, dosed per can instructions to avoid thinning the oil
New Champion spark plugs
Dielectric grease on the spark plug boots
Anti-seize on the spark plug threads
Spark plugs torqued to 20lbs per service manual
Fuel pump filter screen removed and cleaned, then put back in
No fuel leaks anywhere
Spark on all cylinders
Compression not checked
Carbs clean and looking new, no corrosion, trace varnish in bowls
Remote controls, cables, have not adjusted
Newer battery, fully charged
Old steel gas cans, but no sign of rust or corrosion that I've seen
Newer Attwood fuel line and bulb.
I think that is about everything I can think of.
