1973 merury 850 will not idle

[Kmyers]

Thanks for taking a look at this, my problem is that my 1973 mercury 850 will not run except for high idle with warm up lever all the way up. If I bring it down a little it will miss every so often until eventually I will tap the choke and it will pick back up and run a little bit and start missing about every 5 seconds and keep losing a little rpm eventually I will have to raised warm up lever back to all the way up position and tap choke and it will keep running smoothly on its own again. This is what I have done. Commpression is 150-150-140-150 with all plugs out and grounded, I have rebuilt fuel pump except for the 2 check valves inside but they seemed to be air tight trying to blow through them. I have rebuilt both carbs including new floats, both idle screws are at 1 1/2 from seated but I also tried 1 3/4 and 1 1/4 out did not do better in the other positions. I have a new primer bulb and all new hoses everywhere. My hose from tank to primer is 3/8 and everywhere else is 5/16. It is about 8 ft from tank pickup to motor and I will have to move my primer bulb because it will not prime so far away. But once fuel was in it seems to be fine. I thought this could have something to do with my problem I will try to shorten this and use a small can and hose. I connected all new wires at the engine harness plug. This boat had set for about 20 years in a barn. I guess I have not run it enough to see anything on spark plugs Im still using the old plugs I know this a long statement I just wanted everything listed. I know I will get some good feed back. Thanks

 

[Maxz695]

Re: 1973 merury 850 will not idle

It is starving for fuel. Leaky line bad fuel pump or carburetor rebuild my be nessecary. Check the fire on all cylinders to be sure all are firing. Cloged fuel filter may be a problem as well. Check compression to be sure all cylinders are worthy. switchbox may not be firing all cylinders. More info is needed narrow it down. start with compression then spark then fuel

 

[kazek]

Re: 1973 merury 850 will not idle

kmyers..start with throttle cables disconected and see if engine works with manually advancing throttle lever.on mine engine carbs are open 2 1/4 turns out.adjust idle screw to as low as possible without engine dying.should be around 800 rpm.check CLAMS CANINO link and sync.these engines are strong runners.

 

[Kmyers]

Re: 1973 merury 850 will not idle

Compression 150 150 140 150 appeared to have strong spark on all plugs so I need to know best next step for checking fuel problems and link and sync. Could not find the clams canino link and sync. Do I have to have a timing light for that? It acted the same with cable unhooked. Could it be that timing needs to be advanced and idle screws need to be backed out a lot more to make it idle down as kasek said with his. I know this motor sit for a long time. I did check idle screw position before I disassembled.

 

[Maxz695]

Re: 1973 merury 850 will not idle

Lowering the idle screw will just advance timing to where it should not be. Set the idle screw as instructed just before touching the throttle cam and adjust the low idle timing screw to get the proper idle. Once the idle screw is set it should not be moved. The low timing adjusts the idle from there and carburetor settings are done as well. This must be repeated when best holeshot is obtained and the lowest idle possible is achieved. Never use the idol screw after it has been set. Best holeshot setting on mine runs 2 1/4 turns out from a light seat

 

[Kmyers]

Re: 1973 merury 850 will not idle

I'm sorry I meant the adjustment screw in carb not the idle stop on plate

 

[Kmyers]

Re: 1973 merury 850 will not idle

So my 1 1/2 turns out is not enough should I go ahead and back it out more?

 

[Maxz695]

Re: 1973 merury 850 will not idle

View attachment 178769The turning of the mixture screw to 1 1/2 only gives you a base to start the engine. Your carburation depends on fuel flow thorugh the jets. You must put the boat in the water and throttle up. If it boggs open it up a bit more and try again. Keep doing this and give it time to burn off excess fuel. When you get a decent holeshot your carb mixture will be set as best as possible for acceleration and starting and running at idol. If you follow my instruction to set the throttle cam that opens the carb lever to just before toching it it wil be at the proper setting. The low idol timing screw is the only adjustment that needs to be made other than readjusting mixture screws for the best holeshot after that. This must be done sevreral times to get best holeshot and best idol. leave the idol screw alone after it is set. Backing out the mixture screws will lower RPMs and you must screw the low timing in to raise the idol to where you can put it in forwards and not stall. PS All carburetors must be opened evenly at the same time and the same amount. You can try to tweek it later if you wish. Another PS If this is a 4 stroke do me and you a favor check all lines to the carbs and make absolutely sure there is no leaking lines to the carbs. If you have a leaking line on a 4 stroke you can burn a piston and ruin your engine.

 

[Maxz695]

Re: 1973 merury 850 will not idle

Yes much more but open them evenly a bit at a time until you get a decent holeshot

 

[Kmyers]

Re: 1973 merury 850 will not idle

Your picture is a different motor than mine but all my screws are labeled I am going out now to see what all of the labels are, I have not moved any of them. I will put a picture of them on here in a minute. And hopefully you can give me the sequence of adjusting with my picture. Thanks

 

[Maxz695]

Re: 1973 merury 850 will not idle

I have a 70 HP I can take your picture and hopefully edit it for you but i,m out of here soon. I will be here at about 8 am in any case. I,ll be up for at least an hour more I hope I can help. View attachment 178778 Basically the principals are the same. View attachment 178780

 

[Kmyers]

Re: 1973 merury 850 will not idle

Top left screw is throttle stop, bottom left is spark advance and bottom right is idle stop. My pictures don't seem to want to work but this is how they are noted

 

[Maxz695]

Re: 1973 merury 850 will not idle

Those crabs are more like my EX 40 HP. The throttle stop, stops the butterflies before the butterfilies close completly and stick and it should be set to stop them before the carb lets them hit the housing causing sticking. Adjust it so they dont.the spark advance would be the one you need to use to set the idol for best idol and the one you will adjust after best holeshot and readjust for best idol. This would take several tries along with mixture adjustment to get the best holeshot and idol under 1100 RPM.Could go as low as 960 RPM depending on the reeds the lower the better. I would like picturs of the electronics switchbox or distributor rectifier regulator linkages carb mixture screws coils etc if possible. Definitely open the mixture screws and try to get the best holeshot as I described in the previous posts. This will bring you to where you want to be. Again timing for idol and air mixture for hole shot should make it start right and run right. after looking i see it is a distributor model. Truely i,m not firmilar but i would think the same prognosis applies Being a distributor it,s possibly a 4 cylcle but again timing and fuel are the same in setting the set up. It must be done for best idol and best holeshot

 

[Kmyers]

Re: 1973 merury 850 will not idle

Right now it will not idle down enought to try and put it in gear I am only running on muffs until I can get it to idle. I will get some more pictures

 

[Kmyers]

Re: 1973 merury 850 will not idle

Here are some more pics ignition box is on the very front in front of carbs

 

[Maxz695]

Re: 1973 merury 850 will not idle

Nice engine. First check where the cam hits the carb lever to be sure it isn,t just but before touching it. all adjustments are going to mabe made after that. You may have to look into the carb throats to see they are fully closed.

 

[Kmyers]

Re: 1973 merury 850 will not idle

Ok I set the idle stop screw just before touching the carb cam

 

[Maxz695]

Re: 1973 merury 850 will not idle

Sorry if your engine was running ok before you did carb adjustments don,t touch anything yet I had a smoke break as I don,t smoke in the house. close your mixture screws to a light seat and open 2 turn this will bring you idoll down. if it seems to be still too high let me know.

 

[Kmyers]

Re: 1973 merury 850 will not idle

I am not set up to start right now it's dark and raining I am just making the adjustments I can and will try again tomorrow. And you take all the smoke breaks you want or need. I am adjusting mixture screws out 2 turns now

 

[Maxz695]

Re: 1973 merury 850 will not idle

it can take from 2 to 2 1/2 turns to get it where it needs to be take your time Ill se you in the am. hopefully we can get this adjusted and running like a champ.