Mercury 850 Won't Idle

[AlwaysTradin]

Happy Memorial Day all, Have an issue with a new to me 1973 Mercury 850. I'm not new to outboards and have fooled with them for more than a decade but mostly to part them out. Rarely to resurrect one. Bought this motor to put on a small 17ft V-bottom fishing boat and here's my issue and what I've done so far.

Boat won't idle. If I do get it down to an idle it simply dies the second I shift it into gear. Now I didn't use the mercontrol. I have a dual lever quicksilver controller that I had on a center console and have mounted it in the boat. Ive adjusted the cables accordingly so don't think thats an issue. Hooked up on controller for throttle and the other for shifting since I had no way to have a fast idle lever. Put an electronic choke on the console and everything works well. Never heard this motor run and bought it without checking it out thoroughly. I part ALOT of motors out online and figured if nothing else thats what would happen to this since I gave $250.00 for the motor, trailer and a 1974 bass boat thats in fair shape other than a broken transom. Anyhow. After each step that Ive done Ive backed it into my pond and had the same result. When I can get it down low enough I feel its safe to shift into gear it will die. Occassionally.

Powerhead has been rewired with newer wires as I assume old ones fell apart. I ran new wires for the most part from the console back.
Motor has compression of 135-14- PSI on all 4 cylinders.
Good spark on all 4 cylinders.
Took carburetors off and completely disassembled. Someone had been there before me recently because they were very clean. No plugged jets or anything. Floats looked good. Inlet needles were clean and moved like they should.
Took fuel pump apart. Diaphragm may have been a little stretched but looked good with no holes or tears.
Performed link and sync.
Waters good and all else seems good.
Replaced all fuel lines.

Motor just will not go into gear at an idle without dieing. Will set and idle and occasionally just die instantly like you shut the key off. As soon as you hit the key it fires right back up. What have I missed? Where do I go from here? I've got to believe it's a fuel issue but feel like I've gone through everything fairly thoroughly.

Usually I'm not in a rush but I'm scheduled to go do some camping and trotlining in 4 days with my wife and children and right now all eyes are on me to get this boat done. Any help or suggestions will be greatly appreciated.

 

[Chris1956]

Well, that is a symptom of incorrect idle mixture adjustment or possibly the idle is too low. Mix up a tank of fresh 50::1 fuel. Adjust carbs to get fastest idle. Now try to accelerate. The motor will likely stumble or stall. Open the top carb 1/8 turn and try to accelerate. If it doesn't accelerate smoothly, open bottom carb 1/8 and retest. Repeat sequence until you have an acceptable idle around 950RPM and smooth acceleration. Remember idle stop screw above distributor sets the idle speed.

 

[AlwaysTradin]

Chris thanks for the reply. Last night I went completely through everything again. Carbs are clean as a whistle and I'm fairly sure that its not a fuel issue now. Fuel pump seems to be working as it should. I've started out at 1 1/2 and opened a little at a time on the carbs and no matter what it doesn't seem to make a difference. I can run it at 2000 or so RPMs (by sound don't have a tach) forever but when I try to back the idle adjust screw out on the distributor it won't get down very low without dieing. I have managed to shift into gear but at very high RPMs (1500 or so) and we all know thats terrible for a lower unit. Hard to believe that its giving me this much trouble. When I did the link and sync I did so without a timing light and I'm wondering if I'm off enough on the timing to cause this issue? I've checked that the timing belt is right and everything seems to be fine on that end. Also as I did the link and sync a couple times I've found that the spark advance screw has to be screwed in as far as it will go and that just seems a little odd. Could I have such a timing issue that its causing my troubles? If it is timing wouldn't it show issues at 2000 RPMs as well? Thanks for any help!

 

[Chris1956]

The carb idle circuit has no effect above 1200RPM. Since you cannot get it to run slower than that, no adjustment of the carb will have any effect.

You need to resolve your timing issue. Timing marks are on the cowling support I believe. They are not super accurate, but should work OK. Remove the spark plugs and use a screwdriver to set the top piston to top dead center. See what timing marks match up. Remember the outer flywheel could be put on wrong.

The carbs should begin to open when the timing is 4-6* BTDC. The brass collar on the distributor rotates to set that timing specification.

Max timing is set by the max advance screw. The spec is 21* BTDC

The Idle stop screw sets the idle speed. Try for 900 - 1000 RPM on the flusher.

 

[Faztbullet]

Labyrinth seals worn on reed blocks or skirts worn on pistons and has low crankcase pressure...typical signs of a worn motor that wont idle or go in gear and die

 

[AlwaysTradin]

Thanks to all who replied. You all may get a good laugh out of this but last week I (don't know why I didn't do this to begin with, guess I'm an idiot sometimes) I went thru some other flywheels I had and at that point it dawned on me that I timed the motor wrong. I assumed (again like an idiot) that the 3 vertical dots represented 0 when in fact it does not represent 0. My flywheel didn't have the decal on it but all the others I have laying around (15 or more) do have the decal and at that point I knew exactly what Id done. After timing it (correctly this time). The issue has been completely resolved. As I said earlier I've parted them out for a decade or more but very rarely resurrect one and on that rare occasion it's usually just carb issues or something similar on small fishing boat motors. Again thanks to all for the suggestions and hope you guys get a good laugh out of that. I didn't think it was so funny that particular day but now everytime I look at it I think boy its a good thing I just part them out so the REAL mechanics can have good parts to work with.