Late 80's Mercury 200 V6 shakes and smokes, prop problems

[angterry]

Hello to all, I am looking for a few answers that I am hoping someone could help me with. I have a late 80's model Mercury 200 on a 24' deck boat. Motor has always ran fine, but has always shaken and smoked at idle and no wake speed. I mix 50:1 and use Pennzoil Marine TC-W3 Premium oil. I run sea foam in every other tank. I full up (half tank, 30 gallons) every week. It seems like the smoke is coming from the the small square on the rear of the motor just above the water line. I thought that this was a through the water exhaust, or am I incorrect? There is no smoke in the cowling. Boat was on salt water for a good chunk on it's life, but has been in fresh water for the past 5 years and gets used about 4-5 times a week.

Second, could having the wrong size prop cause the problem? The reason I ask, is at WOT with a 19 pitch aluminum prop I am pulling 7200 rpms and only running around 34 mps. I believe that I should be around 6500 rpm, so I need to go to a 21 or 23 pitch prop, but just havent found the right SS prop yet (I hate to buy the wrong size, so I am trying to find one to borrow for a day).

I thanks you all in advance for any help that you can provide me. Thanks and have a great day

 

[Dave1027]

Re: Late 80's Mercury 200 V6 shakes and smokes, prop problems

The small prop is not causing the smoke. That has to be something else. But 7200 RPM is too high. I think 5800 is about where you should be. Better get the 23 pitch and make sure you got the correct diameter too. A large boat should have a big prop.

You should probably do a compression test to rule out damage.

 

[angterry]

Re: Late 80's Mercury 200 V6 shakes and smokes, prop problems

Dave1027 - Thanks for responding back. I have done a compression check and have 120 across the board. Plugs looked good, but replaced them and all plug wires a few months ago. We use this boat alot, and other then the huge smoke cloud when we take our "booze cruise" every night, I love the boat.

Wow, you helped me confirm that I need to go to the 23p prop. I will find one and put on this weekend and see if I gain any top end speed. I will let you know how it goes. Once agian, thanks for your help!

 

[Dave1027]

Re: Late 80's Mercury 200 V6 shakes and smokes, prop problems

Dave1027 - Thanks for responding back. I have done a compression check and have 120 across the board. Plugs looked good, but replaced them and all plug wires a few months ago. We use this boat alot, and other then the huge smoke cloud when we take our "booze cruise" every night, I love the boat.

May want to go through the carbs and adjust the idle mixtures. That may fix the smoking problem. What does the smoke smell like? If it has a gasoline smell then what I said about the carbs and idle screws should help.

 

[Mi duckdown]

Re: Late 80's Mercury 200 V6 shakes and smokes, prop problems

make sure your tach is reading right before making any changes.

 

[angterry]

Re: Late 80's Mercury 200 V6 shakes and smokes, prop problems

May want to go through the carbs and adjust the idle mixtures. That may fix the smoking problem. What does the smoke smell like? If it has a gasoline smell then what I said about the carbs and idle screws should help.

Has an oil/fuel smell. The smoke is so bad that I can wash and wax the rear of the boat and with-in an hour, the rear will be black. I will look in my motor repair guide about adjusting the idle screws to see if it will help.

 

[angterry]

Re: Late 80's Mercury 200 V6 shakes and smokes, prop problems

make sure your tach is reading right before making any changes.

Seems to be working just fine, is there a way to verify/check it? My reapir book does not mention much about the tach.

 

[Faztbullet]

Re: Late 80's Mercury 200 V6 shakes and smokes, prop problems

Has an oil/fuel smell. The smoke is so bad that I can wash and wax the rear of the boat and with-in an hour, the rear will be black.

Check for carbs slightly flooding or the recirclating valves(bleed) are stopped up

 

[aussieflash]

Re: Late 80's Mercury 200 V6 shakes and smokes, prop problems

With oil injection system your outboard would only be using 100/1 at idle and 50/1 at WOT.So its now premixed at 50/1 and bound to smoke at low idle.
If it smells like petrol I would check carbs for flooding.
Next time it shakes check all cylinders are firing,and inspect plugs.

 

[Dukedog]

Re: Late 80's Mercury 200 V6 shakes and smokes, prop problems

This.............

Check for carbs slightly flooding or the recirclating valves(bleed) are stopped up

and this......

Might be time for carb cleaning, new gaskets. Float, needle and seat check. There are NO adjustment screws on those carburators. Might wanna check idle timing also............jmo