1975 Mercury 850 bogs down when put in gear

[nashton]

My 850 bogs down when I put in gear.
I have to "hole shot" the motor to get the boat going.
And then I am fine.
What I mean by "hole shot" is that I rev up the engine and slam it into gear and give it full throttle and then I get going.

Otherwise, if I just put into gear and give gas it bogs down and dies.

Any ideas on the problem?

 

[Chris1956]

Re: 1975 Mercury 850 bogs down when put in gear

If you continue to "holeshot" that motor, you will not have an issue much longer. Your gears will be shot.

You likely have the carb idle mixture set too lean. Open the top carb 1/8 turn and see if acceleration (the normal way) improves. If not open the bottom carb screw 1/8 turn and try again. Repeat id necessary. If you cannot get descent acceleration, either the carbs are dirty, or they are still not adjusted correctly. Sometimes a shot of choke will allow the motor to rev up.

 

[nashton]

Re: 1975 Mercury 850 bogs down when put in gear

Thank you! Any other thoughts out there?

 

[Motor Boater Bill]

Re: 1975 Mercury 850 bogs down when put in gear

Adjust the idle mix with the motor in the water and in foward gear. Adjusting Idle mix in neutral will result in mix too lean and the symptoms you describe are typical of that condition. Once you get it to idle in gear, adjust both carbs for best idle in gear.

 

[Jacklake2003]

Re: 1975 Mercury 850 bogs down when put in gear

We had/have a 1976 850 that did the same thing. My father is pretty good at carb adjustments and he couldn't get it to run properly. It's been in the family since it was new and it did it from the begining. He could get it to idle nice and transition into forward just fine. In fact, it was one of the smoothest running engines you have ever seen. However, when you "gave it the beans" it would stall. He could adjust it so it had a great hole shot and ran great WOT, but it wouldn't idle very well and stall half the time when it was put in gear.

I have read since on-line from another posting that the problem was likly due to a bad spark advance curve. Meaning, the mechanical advance was not calculated properly at the factory. Therefore it would never run right except under perfect conditions. Not sure if that the problem with yours, but it's a thought. I remember quite well during my youth on the lake in the 80's all of those 70's/early 80's inline 4's and 6's running like crap until you got them going.
Chris

 

[Fuzzytbay]

Re: 1975 Mercury 850 bogs down when put in gear

As Chris said, its pretty much a low speed idle mixture problem. I would recommend you redo the setting. With the boat in the water, (at the lake not muffs or a barell etc)turn the idle mixture screws clockwise till they are "lightly seated" (turn them in untill you feel it stop) Now back both screws out 1 1/2 turns (CCW) start the motor, with it warmed up lower the idle lever down, and then starting with the top carb, turn the idle screw in 1/4 turn at a time, wait a second or two, do this until the motor starts to stumble. Back out the screw 1/8 turn from the stumble point. IF the motor stalls out, just back out the screw a 1/4 turn and try again. Now do the same on the other carb. Once you have this set, take her out for a hole shot. IF it stumbles, turn BOTH screws out one blade width (16/th turn), and try again, keep this up till you get a good hole shot, and your done.

 

[Fuzzytbay]

Re: 1975 Mercury 850 bogs down when put in gear

We had/have a 1976 850 that did the same thing. My father is pretty good at carb adjustments and he couldn't get it to run properly. It's been in the family since it was new and it did it from the begining. He could get it to idle nice and transition into forward just fine. In fact, it was one of the smoothest running engines you have ever seen. However, when you "gave it the beans" it would stall. He could adjust it so it had a great hole shot and ran great WOT, but it wouldn't idle very well and stall half the time when it was put in gear.

I have read since on-line from another posting that the problem was likly due to a bad spark advance curve. Meaning, the mechanical advance was not calculated properly at the factory. Therefore it would never run right except under perfect conditions. Not sure if that the problem with yours, but it's a thought. I remember quite well during my youth on the lake in the 80's all of those 70's/early 80's inline 4's and 6's running like crap until you got them going.
Chris

I suspect it need a link and sync, the mechanical advance to adjust the max advance angle is not fixed on those motors, and needs to be set, either mechanicaly with a dial indicator, or with a timing light, depending upon the years.