dies when put in gear...unless in up position

i have a 1975 Merc 800. i got the boat and motor free from a buddy that hasn?t used it in probably 9 years. I cleaned up the carb?s and changed the gear oil. It starts great and idles just as well; the only thing is when I put it in gear it dies. I had the motor in the up position waiting for a friend to go get the trailer and decided to start it up. It seemed to idle a bit different so i put it in gear and it worked great in forward and reverse. Any ideas on why, I am not very mechanically inclined, and this is my first boat ever so any help would be Great!!:redface:

Re: dies when put in gear...unless in up position

Hey you want to also take out the fuel pump and clean it out also. Check all your gas lines. Make sure there is no dirt from dirt dobbers seeing that the motor sat that long. Make sure you have fresh gas in the gas tank. Oh and never tilt the motor all the way up and run it. That can cause your carbs. to get flooded. Also make sure you have water runing on the motor with a water hose and some earmuffs on the lower unit. Or put the lower unit in a huge barralle of water. With out water a baot motor can overheat rather quickly. Do not put it in grear while out of water this could also cause damage. Try looking at spark plugs make sure they are not getting water on them or caked up with black oil. Clean them off put them back in. There might just be something blocking fuel and when you tilted it up the blockage moved out of the way. Check the fuel pump. All the gas lines for cracks dirt ect. Hope this helps.

Re: dies when put in gear...unless in up position

Ran OK up but dies in gear at idle when down in the water.

The difference is the amount of exhaust backpressure caused by being down in the water.

The cure is to readjust your idle mixtures screws OUT (CCW) about 1/4 turn.

Once you have it idling in gear trimmed down such that the carbs are level, then readjust the idle screws (still in gear) to get your best idle speed from the motor. Now further open the idle screws about 1/8 turn.

Your final test is to rapidly open the throttle completely, the motor should accelerate the boat smartly with NO hesitation of bog. Any slight throttle bog or hesitation shows the motor needs just a little more fuel, further open the idle mixture screws just the width of the screwdriver slot. Retest acceleration until all bog/hesitation is gone.

Re: dies when put in gear...unless in up position

Thanks! i will check both of them tomorrow!

Re: dies when put in gear...unless in up position

You said it sat for 9 yrs? I would check the impeller(replace water pump) I had a51 merc do basicly the same thing IN barrel of water it run fine. Put boat won the water idle fine put it in gear died every time. Sold boat to friend and he found out it was waterpump. Ran like a scared rabbit after that. Now kind wish I never sold it. Now own 4ft smaller boat and restoring it.

Re: dies when put in gear...unless in up position

check under engine faqs and look at awakeing a sleeping outboard ...... will give you a step by step on what to sheck for and do to prevent engine damage and get you up and running good