1970-75 Merc.850 / settings for screws

[milwfire90man]

I just bought a "68" 15 1/2' V-hull with a Mercury 850 Thunderbolt Ignition {unknown year.early 70s}.This is my first boat. The gentleman I bought it from knew less about boats than I do.Long story short it die on the water and before he found out he didn't have the battery cable tight he was messing around with three screws by the distributer. I think one was ignition spark?? The other two I dont remember maybe high/low adle.{Sorry am at work} Anyways does anyone know the proper setting.{bottom out _# turns ?????} Thanks.

 

[Ben Konopacky]

Re: 1970-75 Merc.850 / settings for screws

My dear sir,my bets advice to you would be to first get a service manual(merc prefered) and get acquainted with your new buddy.and most of the info. will be at hand,and we then can steer you in the right ditection.

 

[DHPMARINE]

Re: 1970-75 Merc.850 / settings for screws

Un-buy the boat until you see it run correct in the water.Frankly,if it has any single problem,the fix is more than the motor is worth.<br />Sorry,DHP

 

[Chris1956]

Re: 1970-75 Merc.850 / settings for screws

Fireman, The three screws on the distributor plate are idle stop, max spark advance and max throttle. They are labeled. Idle stop is easy to set, it is the minimum speed you want the motor to run. Max Spark advance is set with a timing light, and limits the spark advance to the Max specification for your motor. Max throttle is easy to set, open the throttle (notor not running) until the carbs open all the way to the stop. Tighten the max throttle screw until snug, then tighten the lock nut. Once these are set, they are ususally left alone uhtil one does a tune up!<br /><br />The carb mixture adjustments are at the two-o-clock position on each carb.

 

[emckelvy]

Re: 1970-75 Merc.850 / settings for screws

Set the max spark advance at no more than 21 deg BTDC at cranking speed. <br /><br />You can also do this underway, but you need a second person and must be very careful!<br /><br />Make sure that, when you adjust the carb stop, the carb butterflies are just fully open and are not "overcentered", which will reduce performance.<br /><br />BTW if you have no idea how long it's been since the water pump (impeller) was replaced, you might consider doing so. Cheap insurance (under $25 for the impeller) vs. the cost of a burnt-up motor.<br /><br />G'Luck.........ed

 

[milwfire90man]

Re: 1970-75 Merc.850 / settings for screws

Chris1956 & EdMc. Thanks for your replys they will be very helpful.