Motor bogs down in water when accelerating

[Bke12345]

Hey all. So I got my boat in the water, finally!! After a lot of time and money. I got a 1979 Mercury 150 outboard in-line 6 with 3 carbs. Have an issue because I’m trying to figure out why the motor bogs down when I try to accelerate in the water and it stops every time. I can accelerate all day long on water muffs out of water but when I put in the water and try to accelerate it bogs down and dies every time. Does anyone know what would cause this and is there a way to just I guess the carbs?

 

[racerone]

Just try and open the 3 low speed mixture screws 1/8th turn and test run.----Repeat as needed.

 

[Bke12345]

Is that the little brass screws that’s close to the top of the carbs?

 

[Bke12345]

Where the little hoses go from one side of the carb to the other side of the float bowl?

 

[racerone]

You should be able to find a screw ( spring on it ) at the upper right side on front of the carburetors.----Not brass either.

 

[Bke12345]

Where the little hoses go from one side of the carb to the other side of the float bowl?

 

[Bke12345]

Oh ok. Well what would be the brass screw for on it. It has a hole in the middle of it. Would that be your oil fuel mixture?

 

[racerone]

Stop looking at the little hose and brass screw with the hole !------That is something to do with a " back drag " feature.----It leans the motor out at full throttle.----And nothing to do with oil mixture either.-----Look for a screw with a spring !-----I don't mind trying to help but perhaps a factory manual should be on your wish list !

 

[Chris1956]

Mercury did not make a 150HP inline six motor in 1979. The last one was in 1977.

However, they made a 140HP inline 6 in 1979. If you want to get the right parts or a manual, you should search motor year by serial number.

BTW - Racer is dead on. If the motor idle well, the carbs are likely too lean for acceleration.

 

[racerone]

Serial # should be posted.----Should almost be a requirement to allow posting on various sites !

 

[eddiesweber]

I had the same problem with a 1968 Merc 1000. I thought I was adjusting the carbs wrong, but it turned out to be a compression problem. Here is the procedure I used to find the problem. First, I spent days trying to adjust the carbs. The engine would run great until I put it in the water and I would have the same problem. I eventually noticed that if I adjusted the bottom carb (of 3), nothing would happen? If I adjusted either of the top 2, I could make the engine die or start running rough. So I spent a bunch of time trying to adjust the bottom carb, but it would just do nothing. I decided to tear the engine apart and while I was cleaning it, I noticed a hole on the side of the block!! It looked like a bullet hole? Once I noticed that, I went down to O'Reily's and borrowed a compression tester. Sure enough, there was almost no compression in the bottom 2 cylinders. Ouch. I think he top 4 cylinders would keep the engine running when it was out of the water, but as soon as I put a load on the engine it would bog down and die. Go borrow a compression tester from your local O'Reilys and make sure you have compression on all 6 cylinders before you keep trying to adjust the carbs.

 

[Bke12345]

Sorry. Didn’t mean to put 1979. I have a 1977

 

[Bke12345]

I have an update on the bogging down on load problem. When on the water Sunday I tried to adjust the carbs in forward gear as I read on to do. It seemed to work alittle And I accelerated and it seem to work. But not fully. I got it home and parked the boat for the day. The next day I put a barrel under it and tried the process again with a load. Now this time I can’t seem to get the engine to even start up. It’s like I did something to the adjustment on the carbs to which now I can’t seem to figure how to link and sync them to get the engine to start back up. Any thought on how I could go about this to get the engine to start back up to proceed the process on the load?

 

[Chris1956]

Set carbs 1-1/2 turns open from light seating. That will allow it to start, and idle.

I am not sure how you intend to set carbs in a barrel. If you had a test tank (large, covered tank), plus a test wheel, it could be done on land. Barring that, the water is the way to go.

You did set the throttle primary pickup timing and max timing, right?