Merc 850 random starting

[winsarah]

Been pouring over these forums for a couple of weeks now and have decideed its time to humble-up and ask.<br />Mercury 850, 1975 sn#442073610066. Ran great last summer, did not winterize at all (I know...bad). Strong cranking over, only have spark when the key starts the crank, and then will give another spark when key lets off- no spark in between. Have charged the battery and am in the process of repairing crumbled wires...every replacement brings up two more bad ones! I always try to start when done with a replacement and now when I engage the electric choke in rapid succesion, it gets the motor to pop like its wants to start. Have disconnected the choke and get the original "key turn, one spark, key off, one spark. Sure wants to fire off the one spark though. I have disconnected the tilt switch, no change. Hope this is not too long winded.<br />Thanks in Advance!

 

[tashasdaddy]

Re: Merc 850 random starting

i have a 71 1350. it sounds like your wiring is likw mine was. insulation falling off. i opened my controller, i have no idea how it ran. everything was bare,corroded, choke switch fell apart. i found a new/old stock controller on ebay, and a new internal wiring harness from oldmercs.com. it's like a brand new engine, except the water pump went out this week. your spark situation points toward bad ignition switch. man it's 31 years old.

 

[winsarah]

Re: Merc 850 random starting

Thanks tashasdaddy, it is old and sitting expose all winter wasn't the best thing. I will take a look at the controller. Anything I should be careful of when doing so? , i.e, springs popping out, cables getting misaligned, etc.<br />Thanks

 

[tashasdaddy]

Re: Merc 850 random starting

disconnect the battery before starting, i'm 99% positive you will find bare wire from cracked insulation. and mine was a freshwater boat.

 

[tashasdaddy]

Re: Merc 850 random starting

just looked at Ebay. if you have the big elect. plug on the side of the motor there is a controller. ebay # 4642085947 $75.00 looks good for used. says harness is in good conditon, but cables are stiff. you could use your cables.

 

[winsarah]

Re: Merc 850 random starting

Thanks again, I will open it up in the morning and probably just bid on the unit, wish it was a buy now option...you know.. "I need it yesterday".<br />Thanks

 

[timmathis]

Re: Merc 850 random starting

Also could be a bad ignition switch, Or it could have a bad trigger. If it is not in the wires.<br />Take your time and do it right you will be happy in the end. Good Luck, Tim<br /><br />P.S. Click on the link below for a good troubleshooting guide.<br /> http://www.outboardparts.com/mercury/troubleshooting/printguide.htm

 

[roger3645]

Re: Merc 850 random starting

Kiter, if you still have the problem after fixing your bad wires. Check the wires of the switch box. If they are ok then try using a jumper wire to connect the red wire to the white wire on the switch box. This will give you constant power to the ignition system. You'll probably have to choke the motor in order to shut it off. If the motor runs like this, then you may have a faulty switch box. But make sure you check the wiring and key switch on your controller first. You could have bad wiring in there.

 

[winsarah]

Re: Merc 850 random starting

Thanks for the input roger. I have yet to get into the key switch. I am still finding corroded wires and replacing them. I did notice the other evening that there is an occasional visible spark coming from the coil wire at the distributor and at the other end. I tried the jumper of red to white, no start, but that was prior to fixing the badly corroded red wire. Will try the jump again when it stops raining.<br />Am thinking of replacing the plug and coil wires, not sure where to get them.<br />Thanks

 

[roger3645]

Re: Merc 850 random starting

Try oldmercs.com

 

[winsarah]

Re: Merc 850 random starting

Have looked there and came up with part #84-63212A 2 for the wires- is that correct? Not sure about which coil wire either. So with the spark/arc that I am seeing from coil wire area, is this a large part of my problem or just another small piece of the larger puzzle? <br />Pretty sure I know the answer, but just need some guidance and justification for the purchase of said wire.<br />I really appreciate the help from everyone!

 

[roger3645]

Re: Merc 850 random starting

Kiter, that coil wire looks a little short to me. Maybe for a 1973 model. I have both, a 73 and 75 850 mercury. On the 73 model the coil is mounted closer to the distributor. I'd go with 84-821945A37 appears to be the same but just a bit longer. I'd say that arc is a big problem especially since these motors dump fuel out the front of carbs. Check Dist cap from cracks.

 

[winsarah]

Re: Merc 850 random starting

Hi Roger, have checked distributor and did not find any cracks. I am purchasing the 28" yellow plug wires and the coil wire you suggested. Also will get the NGK BUHW plugs...and a manual!! Aside from the fire potential( i want it to fire in a different way), will the arcing affect the starting.<br />Thanks again

 

[roger3645]

Re: Merc 850 random starting

Kiter, I'm not ignition savy. But I'd think if it is arcing at the coil wire then the charge might not be getting to the spark plugs. Try using the advanced search and search "Arcing Coil Wire". Sorry I can't be more help on the topic. But maybe someone else can. If you don't find anything in the search start a new thread titled arcing coil wire. I think the arcing is your starting problem. Try removing the coil wire and taping it up with electrical tape to see if you get spark to the plugs.

 

[roger3645]

Re: Merc 850 random starting

Kiter, just found this comment:<br /><br />JT, Spray some 50::1 fuel mix into the carbs and crank it. If it starts and dies, your carbs are either dry or dirty. If it doesn't start, you have no spark at the plugs. <br /><br />Also, make sure none of the plug wires or coils arc to ground, or the motor will never start. <br /><br />So I guess it is the arcing causing it not to start.

 

[winsarah]

Re: Merc 850 random starting

Great! Thanks Roger, I will keep you posted.

 

[Chris1956]

Re: Merc 850 random starting

Kiter, OldMercs is the cheapest place to buy the Spark Plug wires. I bought some there and reused the boots and springs. The wire from the switchbox to the coil should be a good stranded wire of AWG#12 or thicker. Make sure the ground wires on the distributor body are good. Make sure the rotor and cap are clean and dry. Remember the rotor does not come off the shaft. Use some 220-400 grit sandpaper to polish it up.

 

[winsarah]

Re: Merc 850 random starting

Thanks Chris, I have placed the order and will keep on tinkering until the stuff arrives. I appreciate the advice.<br />Thanks!

 

[winsarah]

Re: Merc 850 random starting

OK, tashasdaddy, you found the controller that would work for my engine, but it is not available anymore. Have the manual now and plug wires and am pretty sure you are on as the key switch being the problem. Any ideas for where to buy now?<br />thanks!

 

[tashasdaddy]

Re: Merc 850 random starting

found 2 possible not in as good shape as the other one. will keep looking daily. ebay#4645343011 $51.00 no key, 4644837312 $9.95 did not see key in picture, key can be ordered from old merc.com all you need is the number of the switch.