1984 mercury 150 blackmax timing/ link and sync procedure

[cam1399]

I have a 84 mercury 150 blackmax. The boat sat for a year. Just got it and having trouble reaching WOT in water. It takes forever to get on plane and will only hit 4500 max rpm trimmed out. 23p stainless prop that gets looks black from the smoke. Compression is even on all cylinders. 115 and 120 with 2 different compression testers. I have replaced both switchboxes. One was bad. I replaced the stator and now runs better but still wont hit rpm. Before I could just get 3200rpm. I have cleaned the carbs but may do them again. So I am trying to figure out the correct procedure. Do i set timing first then sync the carbs? I have found true TDC to zero for the timing. Do I set idle timing then WOT? After that do I align the carburetor linkage to the center of the roller for the idle stop? Thanks

 

[Chris1956]

A 23P prop would only work on a light fast hull. Must boats have too much drag to allow full RPM. Is the motor, boat or prop new to you? What is it that you have? The prop hub is the right size for the motor, usually 4-3/8"?

Have you checked the fuel pump. A black prop is unusual. Maybe she is pouring fuel out the exhaust?

Link and synch is as follows. Remove prop and all spark plugs. Install #1 spark plug into it's wire. Set throttle so carbs are still closed, but ready to open. Crank motor and check timing. Timing should be 0-9*ATDC. Adjust idle timing screw on throttle arm to make it so.
Set throttle to full crank motor and read timing. Timing should be 21*BTDC. Adjust max spark advance lever on timing arm to make it so.

 

[cam1399]

It is new to me. It is a 1986 winner fish and ski 17.5. I thought it was a little over propped but not that bad.

I rebuilt the fuel pump.

So close the throttle then set timing. Wot is correct. I have idle at 8 atdc. It doesn’t want to idle though. So adjust the middle timing screw for correct rpm right?

Before all this do I adjust the idle stop screw to center the roller?

 

[Chris1956]

You probably want a 19" or 17" pitch prop for that boat. In theory, a 19" pitch prop would get you about 5300+ RPM. 17P would get 5700 RPM or maybe some more.

Idle pickup timing is set when the carbs are closed, but about to open. 8* ATDC at that point is fine.

 

[cam1399]

Okay so I will go down on the prop. Any benefit to stainless over aluminum? It has stainless now.

So setting idle pickup timing is done at cranking speed first right? Then start it and adjust idle to correct rpm and make sure the roller is in center with idle stop screw at the bottom? All with carbs closed?

 

[Faztbullet]

Boat should run a 20pTurbo as thats a Hydasport hull that was copied.

 

[cam1399]

Thanks. What is the turbo prop?

 

[Faztbullet]

 

[cam1399]

I’m doing the link and sync and I’m having trouble getting the feeler gauge fitting on the cam roller

 

[Dukedog]

don't worry 'bout tha gap between tha roller and tha cam.. as long as ya have a slight gap and lines line up it will work jus fine.. i've run as much as 3/8ths of an inch gap on some of my hot rods over tha years......

 

[cam1399]

I don’t have any gap at WOT between the roller and cam. It’s pretty tight.

When setting the roller to the cam there are 2 lines. Using the idle stop screw I line the smaller bottom line up to the center of the roller while keeping the carburetors closed then lock them down. Is this correct?

 

[Dukedog]

I don’t have any gap at WOT between the roller and cam. It’s pretty tight.

not supposed ta be... gap is at idle with everything at rest...

When setting the roller to the cam there are 2 lines. Using the idle stop screw I line the smaller bottom line up to the center of the roller while keeping the carburetors closed then lock them down. Is this correct?

idle stop is used for tha lines .. has nothing ta do with carb linkage

 

[cam1399]

Oh okay. I thought you adjust idle stop until the roller and cam just touch in the center before you start your link and sync.