1986 Mercury Classic 50 runs like a dog

[Odbrew]

Hi, I just purchased a 16ft deep v starcraft w/ the classic 50 outboard and this thing runs surprisingly slow (18 mph). It seems to accelerate fine but the top end leaves something to desire. So far I have replaced plugs, checked fuel lines, changed impeller, changed to a new prop 10 3/8ths 13 pitch, checked compression (120 +/- 2 psi) and verified that the carbs are opening all the way. It looks like the switchbox and other components were replaced in 2014. Tomorrow I plan on rebuilding the carbs and verifying timing, anything else I should pay particular attention to? Also I was curious as to if any one had a cheap tach suggestion, my multimeter doesn't want to play nicely with the control box. Thanks!

 

[Odbrew]

Carbs cleaned and rebuilt. I did have a question though, currently the mixture setting is 1 turn out from seated in order for it to run and idle.....is this getting too close to lean ?

 

[GA_Boater]

13" pitch might be a little too much. What is the WOT RPM?

The mixture has to be set with the motor in the water. 1 to 1.5 turns out the starting point just to get the motor to run and the fine adjustment is done in water in gear.

I just back the trailer down the ramp with the boat still tied down and put it in forward at idle and adjust the screws.

 

[Odbrew]

I'm not sure as I don't have a tach for it at the moment. In the morning I will attempt to make it work with my multimeter. I made my adjustments with the lower unit in a tub of water in forward, but its all by ear. I'm skilled with working on regular 4 stroke engines but this two stroke makes me nervous lol. I did notice that one of the coils intermittently triggers the timing light so ill be swapping it around tomorrow to see if the problem follows the coil pack and then do a link and sync. So the potential for it to tune at less than one turn out is not a significant issue?

 

[GA_Boater]

I turn the top screw in until the motor starts to stutter, back it out until it stutters and set it to the midpoint. Then do the same on the lower carb.

Are you in gear in the bucket? It has to be in gear and at idle. It need the water load on the prop.

 

[Odbrew]

Yes I had it in gear, barely enough volume to adjust idle. I did manage to get it to a local lake tonight and do the link and sync, it runs much better but only 21 mph with only myself on board. I'm guessing that the next step is to take a look at the foam to see if its waterlogged? You may be correct in that it is overpropped at a 13 pitch. Thank you for the responses btw.

 

[Odbrew]

Update: After checking and rechecking everything I discovered that one coil was bad, it would spark on my smaller tester but not make the 7/16" gap on a homebuilt one. I replaced it with a cheap Sierra part and now the engine runs strong enough to propel the boat to 30 mph despite all the waterlogged foam. Now I did notice that I have about 1/8th" play front to back with the new prop, its on the flow torque reflex hub that came with it and is torqued correctly. Is this a normal/acceptable amount of play?