How to set timing on 1973 85HP?

[bucchb]

I have just installed a used distributor, in my 85hp Merc.

I am awaiting a manual, and was wondering if someone could explain the base timing setting. The tag on the side of the motor says .172 BTDC , 27degrees. I see the gradations on the side of the motor.
There is also an arrow on the top of the distr. pulley.

I believe there is a "base timing setting" by lining up the timimg "dots" with the dist. pulley, and the spec is for timing advance adjustment. I am not interested in that yet ( although I believe that you bring the fly wheel to 27 Degrees BTDC and turn the dist. till it fires, with a meter on the spark plug and lock the "Spark Adv." screw in that position???)

Could someone help me set the "base timing"???

Thanks

 

[Yepblaze]

Re: How to set timing on 1973 85HP?

There is no base timing, like on a car.

As you might notice the distributor turns all over the place in relation to the throttle control. Even well before any carb action comes into play.

First thing you want to do is confirm that the timing mark and any pointer used is acurately set to TDC.


What is done is you line up the mark on the dist gear with the mark on flywheel.

That is provided that the mark on the flywheel still lines up with the dist gear at TDC.

Which can change if some dummy had to remove all the little bolts that affix the flywheel instead of using a puller.

Then at some point in the distributor rotation the carbs will start opening untill full throttle is reached.

And at full throttle there is a maximum that you want to limit the dist movement at. (Max advance)

 

[bucchb]

Re: How to set timing on 1973 85HP?

I guess youre saying pull the plug on #1. and make sure TDC is TDC!

What you say IS possible. Someone coated the stator wires and I would not doubt it was a dummy. I notices a pencil mark on the flywheel????

Once I have TDC do I set the plug to be pointing at Sparkplug wire #1 like in a car?

 

[Yepblaze]

Re: How to set timing on 1973 85HP?

yes, best method to achieve exact TDC is with dial indicator.


And most important beyond provability is the max advance setting, which can be set with a timing light. If it says 27 degrees, you might want to pull that back 2-3 degrees so you can run today's gasoline without burning a piston.

 

[bucchb]

Re: How to set timing on 1973 85HP?

Well, the flywheel had been moved. I readjusted to TDC. ( the wirng that was on the boat had #1 on the bottom?? but top cylinder is marked #1, so I also redid the wires) Now I am trying to set timing.
With throttle backed of to starting position, do I set the pulley to 27 degrees or at TDC?????

Thanks
Bill

 

[Yepblaze]

Re: How to set timing on 1973 85HP?

At tdc of top piston the mark on the flywheel and the mark on the dist drive pulley (under the plate) all line up. Along with the rotor pointing to the correct location in the dist cap that leads to the wire to the top cylinder.


Then as you can turn the motor by hand (without twisting dist body) note that each next spark plug wire in dist rotation co-insides with the next piston at tdc or there abouts.

 

[Chris1956]

Re: How to set timing on 1973 85HP?

Bill, Timing is set 4-6 degrees BTDC for idle pickup. Idle pickup is when the arm on the distributor just touches the carb throtle plate. There are two bolts hidden in the dissy midsection.. Loosen these and rotate the plate to set idle pickup timing.

Max timing should be 21 degres BTDC. There is a max adv screw that is set and locked in.

A manual would be a wise investment since it is a bit trcky.

 

[bucchb]

Re: How to set timing on 1973 85HP?

Thanks guys. Yeah, I have a manual now.

I am still having a problem. 2 local experts tell me the dots can be many degrees off. They tell me a dial indicator is needed to find the exact TDC? I can buy a dial indicator setup with magnetic base ( will need a piece of steel with a bolt hole for the top of the engine) for like $40.00. SHOULD I BUY IT????

(I have found a pretty good guy locally and am tentatively scheduled for an hour next wednesday. Pretty quick this time of year, and he admits the job is an hour or less. I figure it may not be a bad idea to have a relationship with a good local mechanic, would treats you like an adult, and schedules you in a week or less in May??)

Then the rest is pretty easy with your help and the manual.

Thanks again.

 

[Chris1956]

Re: How to set timing on 1973 85HP?

I set the timing pointer using a caliper. First you measure from the spark plug base on the head to the top of the piston. Now add .464 inches to that measurement. Set the caliper for that measurement and back down the piston that much. Now set the timing pointer to .464 inches BTDC