1973 Mercury 850 spark problems

[StriperLover]

hello everyone i am relatively ner here at iboats But have been working on mercury outboards for a year and a half and am pretty compitant with these motors now but i am stuck here.

First i have some spare ignition parts off of another mercury 850 and they are not the same as what i have on the motor i am trying to repair, and they are both come up to be 1973 model years from the s/n all i can think of is someone didnt want to pay anymore than they had to when repairing this motor in the past and have used anything they could find from a scrap motor.

Ok with that said the switchbox on the motor now has 4 terminals only
A green to the + side of the ign coil
a brown to the tach connector in the controls
a blue lead to the dist.
a red to 12volt +

the one of the parts motor is a 7 terminal box with:
red
green
black
2 brown
2 white

distributor on the motor has 3 wires
white
black
blue

parts motor distributor also 3 wires
white
black
brown

now from research i believe the parts motor ignition parts are the correct parts that belong to this motor and the ones on the good motor to be the odd ones out.

Now for my question with all the background stated i got this motor with no spark i replaced all the plug wires and any main and engine harness broken wires. removed the dist. and cleaned all the contacts in the cap and trigger system inside and then i had spark and the motor ran great on a stand.

I put the motor on the boat and started one more time with new universal controls(converted small boat to center console) and then didnt touch it for 3 weeks while finishing the boat up.

went to the river today and motor would not start. i went all the way home and found NO SPARK again. well i tried cleaning everything again and still no spark. i tried a known working coil i have on it and still nothing i have a bad feeling it is the trigger in the distributor but have no idea how to test it. i have searched for a procedure and have found nothing i have the seloc manual and i love this in the ignition troubleshooting section it says bring the switch box and dist. to a dealer for testing. well if i wanted to pay someone to fix the motor i would not have bought a repair manual.

ok any help is greatly aprecciated

 

[Laddies]

Re: 1973 Mercury 850 spark problems

Trigger test, Ck for 12v on the red terminal and 12v on white terminal with the key on starboard side of the box. Disconnect the 3 wires from the dist. and place a jumper wire between the brown and white terminals and use a wire from the black terminal to arc to ground each arc to ground will produce a spark at the coil

 

[Chris1956]

Re: 1973 Mercury 850 spark problems

StriperLover, The '73 850 motor was a standard battery-distributor ignition with three leads to the distributor (as you probably figured out). Is the 4 terminal switchbox a direct replacement for the original 7 terminal switchbox? If so, how do you wire the distributor to the switchbox?

PS Yesterday I cannibalized my '73 850 distributor to make my '77 1500 run.

 

[StriperLover]

Re: 1973 Mercury 850 spark problems

ok chris on the 4 wire switch box that is on it (which i found to be bad)
the wires were as follows

red engine harness wire to red terminal on the box
brown tach wire to brown terminal on the box
green coil power supply to green terminal on box
blue distributer wire to blue terminal on box

other ignition wires were as follows
white engine harness to white dist. wire
black dist. wire to ground on engine
black coil feed to ground on engine

now i am looking to see why the distributer on there has a blue wire instead of a brown wire. the part numbers is as follows if any one can help on what wires are what on the 2 different dist. assemblies

blue,white,and black distributer-337 4479
brown, white, and black spare distributer i have - 333 3736

also the p/n on the 4 terminal box is 337-4411 vs the 7 terminal spare box i have which is 333-2986.

 

[StriperLover]

Re: 1973 Mercury 850 spark problems

ok today was long but somewhat productive day. first i tried to use the 7 terminal switch box with the distributer with the blue wire and i dont think they are compatable or the distributer trigger is NFG witch i will never know then i had to modify the distributer with the brown wire to fit. the brown wire distributer had threaded holes to bolt it in. the blue wire dist. had nuts and bolts with through holes after that dilema was solved i started the motor at 9:30 PM and had the crazy old ***** next door come outside ramping and raving and all sorts of crazy crap. but the motor that 3 weeks ago ran fine wont stay running under 3500 rpm. all i can think of is that all the timing adjustments are way off now that i had to switch the distributer and switch box. i dont know but i will see unless someone here has some insite as to what maybe i did wrong. well now it is 10:30 and the damn thing still dont run right and i am really tired so off to bed i go. hehe
thanks for all the replies and maybe i will see ya on the water someday.

Billy

 

[StriperLover]

Re: 1973 Mercury 850 spark problems

also i thought you all should know i got the motor 2 monthes ago not running i rebuilt the carbs and fuel pump and replaced all the broken wires it then ran GREAT. i ran it 5-6 times after that just to get some time on the motor before i installed it onto the boat and i ran it 1 more time after the install and it still ran fine then the first time i brought it to the water this whole no spark issue started and now the wont stay running issue.

thanks Billy