1971 Mercury 850 Thunderbolt 4 cyl

[opsmgr]

I am having trouble keeping this motor idling at a low speed. The motor idles with a little bit of throttle. I do not have a tach hooked up properly yet but I have read that I need to hook up the tach lead to the yellow stator wire since I am using a Medallion Tach. (what setting should I use? 1, 2, 3 or 4). What RPM should this motor run at while at WOT? I have not had the motor on the water, just acquired it last month.

I have ordered a manual but have not received it yet.

Any help is much appreciated.

 

[Gomer50]

Re: 1971 Mercury 850 Thunderbolt 4 cyl

I am not sure Mercury made a 850 4 cyl. in 1971.But the 850's 4 cyl. were introduced in 1973 and max rpm range is between 4800 to 5300 @ WOT.

 

[opsmgr]

Re: 1971 Mercury 850 Thunderbolt 4 cyl

My fault it is a 800 4cyl thank you
Any idea what settings I should use on the tach?

 

[Chris1956]

Re: 1971 Mercury 850 Thunderbolt 4 cyl

Normally Mercs take a 12P or 6P setting. Since that is not a choice, give it the Monte Carlo method. Try all settings until you believe one. Idle speed is likely 900-1000RPM. Pick a setting that shows that RPM at idle and test it at throtle.

 

[opsmgr]

Re: 1971 Mercury 850 Thunderbolt 4 cyl

Thank you. The setting that works the best is 4 on the Medallion Tach made February 1985 (in case anyone else runs into this)