1977 850 thunderbolt runs fine on muffs, wont stay running on water

[ccarpen4753]

I have a 1977 mercury 850 thunderbolt. It will run fine on the muffs, but as soon as i put it in the water it wont stay running. Its on a 16ft bassboat. It idles fine and throttles up and down both in gear and out on the muffs, but I can get it to do anything on the water. Fuel lines are clean and has a new primer bulb.

 

[Scott Danforth]

have you checked compression? have you done a linc-n-sync? have you cleaned the carbs?

 

[ccarpen4753]

Dont have a compression tester, no i havent cleaned the carbs. What is linc-n-sync? It just doesn't make sense why it runs great out of the water, but wont run in.

 

[Scott Danforth]

it makes perfect sence why it runs out of water and not in water. the engine only needs to make about 1/2hp to run out of water, and it could be running on 3 cylinders and you would never know it.

if you own anything with spark plugs, you should have a compression tester. they are a free rental tool at most auto parts stores, or spend the $20 and get one.

the link-n-sync is linking and syncing your carbs. if your carbs are dirty, and you are only feeding one or two of the cylinders, the lean cylinders will eat themselves.

 

[ccarpen4753]

ok, 125psi across all cylinders, good spark on all cylinders, cleaned carbs. made sure both move the same. Anything else i need to check?

 

[ccarpen4753]

Ok, well I got it to run in the water decently. Does it have exhaust ports under the block that need to be free of water to start? And it was real sluggish, the boat..not the motor, in the water even at WOT. My tilt trim unit isnt working could the outboard be tilted back too far?

 

[racerone]

This topic is discussed almost every day.----When the lowspeed mixture is adjusted for smooth idling it is too lean for this motor to accelerate !----So a " no money spent " thing to do is to open the low speed mixture needles 1/4 turn at a time and test run !