1977 mercury 850 timing

[radiorich]

I am trying to set the timing on my merc 850 SN4720922. This is the one without a distributer. I am supposed to advance the throttle arm till the primary pick up cam just touches the carburetor tab. The problem is that on my motor, it barely touches the carburetor and NEVER moves the carbs. The carburetors don't start to open till the secondary cam comes into play. The buterflys in both carburetors are fully closed till the secondary cam starts to open them. So where should I have the throttle lever when I set the primary timing pickup? The primary cam does just touch the carb tab, but not enough to start to open the carburetors.

 

[southkogs]

:bump2:

Sorry Rich ... I don't even think I've ever even run a Merc. Let's see if nudging the topic get's some activity.

 

[tommarvin]

I would get a factory service manual , or watch all you-tube videos on timing mercs.
I don't have a clue, is this after you point the timing light at the flywheel for your timing mark.
Should the throttle be set at idle RPM for timing?

 

[radiorich]

Thanks for the reply. I have a factory manual and have watched gobs of videos. I am pointing my timing light at the pointer and, hopefully that would also be at the proper mark on the flywheel at the same time also. I know I have the max advance correct. The pick up timing is what I have been working on. Of course, every time I change the pick up timing, that effects the max setting. The manual says the pick up timing is where the cam just touches the throttle arm (starts to open the carbs). The problem I am having is that the PRIMARY part of the cam NEVER touches the carbs. My carbs don't start to open till the second part of the cam hits the carbs. I don't know where the throttle should be set while setting the primary pick up. I am starting to think that this is not important since we change that any way when setting the idle. It seems like the more I read just confuses things more. I do think that on my engine, the timing should be somewhat retarded at idle. There are no specs for idle timing. What do you think?

 

[racerone]

???----Changing the " pick-up timing " does not / should not change the MAXIMUM timing.------Pick-up timing is the point where the carburetors start to open.--Therefor it is a carburetor / linkage adjustment and not a timing adjustment !!-----Actual idle timing does NOT matter and the further retarded it is the better it is and indicates a motor in good condition.---This is not the same as setting idle timing on a 283 Chevrolet engine.

 

[radiorich]

I realized that as soon as I went back out to look at the motor again. There are two separate ramps on the timing cam, a Primary and a Secondary. The carbs should start to open on the primary ramp and then open wide open on the secondary. I could saw the primary ramp off the cam and it wouldn't make any difference because the primary ramp never comes into contact with the carburetors. There is no adjustment for that. It seems like something is wrong, but I went to the local Merc dealer yesterday and saw a running motor just like mine and it is the same way. I can't figure out why it is made that way, but I guess it is what it is! So now do I time the the pick up timing to when the secondary cam hits the carbs (since the primary never does). When the secondary cam hits, the carbs open very fast and it is almost to the max spark point. And thanks for the reply, I really appreciate it. I am 70 years old and and still slalom ski here. I am afraid that if I don't get back out on the water soon, I may never be able to ski again. I took it out yesterday and got it running fairly good but not good enough to ski. I got it up to 4000 rpm and about 27 mph. I am putting this 85 horse powerhead on my existing lower unit. The previous one was also an 85 horse, but was a few years older and had the distributor and one coil. Both engines are identical except for the ignition system. The old one with the distributor was perfect for 40 years but finally melted the number one piston. I think that was because I found the water pump had blown the top gasket out and I had a loss of water to the top cylinder. Or maybe it may have had a crankcase leak.

 

[racerone]

Have a good look at the linkages / cams.-----Study them.---Look for adjustments.-----And as always I do have a few of those motors and I may look at them to see what you are overlooking.----I would look at my leisure.-------Good on you to be on skis at your age.----I remember the days starting off on a slalom ski in 1 foot of water, gauging the slack in the rope and the " hit it " cry for the 40 hp 1965 Evinrude.

 

[radiorich]

Thanks, I would really appreciate your looking at your engines like mine. I think you will see what I am talking about on the cams. Another question--all the books I have say to set the timing in a test tank, which I don't have. I tried it on the water yesterday, but it was almost impossible to see the timing marks in the bright sunlight. Some people talk about setting the timing while cranking with the plugs out and grounded. My motor is supposed to have max timing at 27 degrees running. What would it be when cranking?

 

[radiorich]

Hi, Racer, I would still be curious if you ever get a chance to look at the throttle cam on one of your engines, but for now, I got my engine running good. I took it outside last night in the dark and set the max timing. While it was running in the dark, I noticed the number one coil was arcing to ground. I replaced that coil and took it to the lake today and it was up to 5000 rpm and 30 mph before I could blink! I do still have to adjust the idle. I think I could tell by the rpm when I was adjusting the primary timing screw and it changed from BTDC to ATDC, Should I be going by the timing light, or just whatever it takes to make it idle good. Then, at what point should I work on the idle stop adjustment? That is currently set so that the carbs are completely closed at idle. I think it is supposed to stay there. It seems like if I were to open the carbs at idle, it would become too rich as it would begin to draw fuel through the main jets as well as the idle jets.
By the way, I used to do the shore start when I was younger, but I am deep starting because it is safer. I see you are in Ontario--I am near Ontario, California, but I bet you are really in Ontario, Canada! Rich