merc 850 1977 no fire but passed the switchbox test

[thibauja]

HI all ...first of all 2 things about me my first languange is french so excuse my spelling and second this is my first post in a forum..and may i say i love this forum...you guys really helped me allready ... i did this test that was posted to test my switch box part no 332-2986a22 looks OK i can get a spark out at the HV wire but no fire at the p^lug
i also read thats if it doesnt fire when starting but only spark once when you let go the key switch (to run position) meens low voltage or bad trigger in the distr. THAt is my problem
is there a way to test the trigger ?
also... being that i just change the distr cap... i realized that there is no mark or nutch to position it ...it can be rotate about one inches ...how do i find the proper alignement ??
do i have to go thru the retiming procedure ?

thanks for any reply..
jack newbie..

The TEST..found here
1. Turn off ignion
2. Disconnect all 3 wires on the distributor side of the switchbox.
3. Remove the HV lead from the coil to the center cap (remember it unscrews
from cap)
4. Reconnect that HV center lead to the COIL side only.
5. Position that HV lead about about 3/8" from ground (block, shrouds etc)
and find a way to hold it there.
6. Jumber the brown and white terminals on the dist. side of the switchbox
together.
RECONNECT BATTERRY
7. Check that you have +12 V at red terminal.
8. Turn on ignition and verify +12V at white terminal (on red terminal side)
9. Touch the black terminal to ground - unit should cause spark each time
thats ok so i guess that prov the switchbox..

 

[ricksrster]

Re: merc 850 1977 no fire but passed the switchbox test

What is your serial number? i have a 1977 850 but I don't have a distributor. It is a CDI ignition.

 

[Chris1956]

Re: merc 850 1977 no fire but passed the switchbox test

The distributor cap should not have 1 inch of movement. There is only one way it fits. I recommend you turn it until you feel it fit without play and then install the metal clamp.

If you have spark at the HV lead to the distributor cap, but none at the plugs, you need to check to see if the spark plug wires are arcing to ground. First check is to remove a spark plug wire from the distributor cap and test for spark on the brass connector where the wire screws in. If you have spark there, you wires are likely bad. if not, your rotor may be bad.

 

[thibauja]

Re: merc 850 1977 no fire but passed the switchbox test

Rick i know both system exist in 1977 but i do have a distrib.. serial 7016871

Chris, plug wire sparc...i m pretty sure by now thats it s the rotor or the small coils in the rotor assembly ( called trigger i think) something like pickup coil in some cars
OR the cabon pin and spring in the distr.. either way im looking a for a complete distrib..and i think i found one ...2 almost complete 85hp real cheap.. but what makes me wander is ... i do get a good spark when i let go the key to run position tyelling me fire CAN get to the plug....so....CAN i TRUST this switch box ??
no fire when starting and one spark when i let go to run position ..does this tell you anything ??
thanks you all
JT

 

[ricksrster]

Re: merc 850 1977 no fire but passed the switchbox test

Yes, you are right . According to your serial number you have a distributor. It is a 1973. Make sure your battery is fully charged. also test your ignition switch.
http://www.maxrules.com/graphics/merc_pdf/merc_page31.pdf

 

[thibauja]

Re: merc 850 1977 no fire but passed the switchbox test

are you saying that it could JUST be not anough power from battery ?? hum ... no chance to take i ll use a knoed good fully charge bat..
swith was tested ..
and you re right i recheced my serial and it is a 73 :-(
my mistake ..

 

[ricksrster]

Re: merc 850 1977 no fire but passed the switchbox test

Always check the simple things first before you start buying expensive parts you might not need to buy.

 

[thibauja]

Re: merc 850 1977 no fire but passed the switchbox test

BTW rick thanks for the PDF file this is gonna be very handy
check simple thing before buying expensive part you say.. LOL funny you say this .... i did buy the switch box for this motor for nothing... this thest i did to validate the switch box.... being that the distrib hv cable is screwed i use and other aparc plug wire connected to the coil..welll.. testing the wire it self is a good idea... cost me 450$ to learn this one... i now have a brand new switchbox to sell... now obviouly i didnt write all this to show how stupid i can be ...but to ask .. you guys must know a good site to sell parts didnt find anything here..
and im gonna have parts from 2 other 85 hp

thanks
Jack

 

[ricksrster]

Re: merc 850 1977 no fire but passed the switchbox test

bammarine.com.Click Mercrcruiser parts. then click search with pictures. Click Mercury. click 850 4cyl. Then click on the first set of serial numbers. or click this link:
http://www.mercruiserparts.com/selectDocs.asp?doc_nbr=63271

 

[thibauja]

Re: merc 850 1977 no fire but passed the switchbox test

just a note to say...
thank you all for help an replys...
i gave up for now on this problem... for the price of the rotor and distrib i bought an other 850 identical to mine (same serial range)
IN WORKING CONDITION
so ill play with this next summer prob to resell

one last question .... im stuck with this new switch box i bought for nothing.... anyone know a good site for selling and buying used parts ?
Jack

 

[ricksrster]

Re: merc 850 1977 no fire but passed the switchbox test

Ebay

 

[thibauja]

im back wit this 850

im back wit this 850

im back after all i cant just scrap this motor for a rotor
first of all i wanan say tank you to all you who reply in this forum this is BY FAR the most helpfull furum i ve seen... it s helped me 3 times so far
here is something i found in this forum about someone who brook his rotor changing the CAP
QUOTE=Chris1956;1235570] Also, you can use a distributor shaft and rotor from a 6 cylinder (90-150HP) motor.[/QUOTE]
really ? on boatfix.com i found this ...
Mercury Distributor Rotor & Shaft Assy (4 & 6 Cyl.) repl 393-4371/4312
my rotor part no is 393-4371 and i can get a 393-4312 from a merc 115
it would be the same rotor assembly ?
i have tested the spark all the way to the distributor event manage to test the little spring and carbon pin....its all good up to there ..but no sparl at any plug so ...
i ve put the ohm metter on the rotor and i have NO connectivity between the center and the edge.. looks like a dead rotor ??
can someone confirme that its the same parts?

thanks in advance
Jacques

 

[ricksrster]

Re: merc 850 1977 no fire but passed the switchbox test

Are there two brown wires connected to the switch box? if there is, one is a mercury switch used to kill the ignition in the event your motor becomes tilted too far upward. Disconnect this wire are recheck for spark. If you get spark then the mercury switch is bad or the brown wire is grounding out.

 

[ricksrster]

Re: merc 850 1977 no fire but passed the switchbox test

That would be the wires on the distributor side of the switch box.

 

[thibauja]

Re: merc 850 1977 no fire but passed the switchbox test

Are there two brown wires connected to the switch box? if there is, one is a mercury switch used to kill the ignition in the event your motor becomes tilted too far upward. Disconnect this wire are recheck for spark. If you get spark then the mercury switch is bad or the brown wire is grounding out.

yap there is 2 brown one comes from the elec choke and the oter on the distrib side comes from the distrib (brown black and white)
are you saying disconnect this last one ?? and retest ?

will try this tonight
thanks

 

[ricksrster]

Re: merc 850 1977 no fire but passed the switchbox test

I sent you a PM.

 

[thibauja]

Re: merc 850 1977 no fire but passed the switchbox test

thanks Rick for the picture ... i have put losts of hope in this mercury switch but....
i ran into an other prob befor i coul dtest it ... the key switch brook or shorted any way i got that one soved but waste more time there and then tested the mercury switch its working fine
thats not it :-( so i m getting a used complete distrib tomorow will se from there.. next ting will be trying to timing the thing...
can any one tell me if i should have continuity between the center of the rotor and the edge that distrib to plug wire ?? caus i dont.. to me a rotor is just a "L" in and out piece of metal if im right that L is broken inside :-(

thank
Jack

 

[Chris1956]

Re: merc 850 1977 no fire but passed the switchbox test

Jack, The rotor does not actually touch the distributor cap, so you will not have continuity. You need to unscrew a wire from the cap and test the wire end to end to see if it has continuity. The wires are stainless steel wire, and should have near zero resistance.

Yu can also stick a piece of regular wire into the dist cap and try to arc the spark to ground, to make sure the rotor and cap are good.

 

[thibauja]

Re: merc 850 1977 no fire but passed the switchbox test

finaly gto an other rotor and took mine off and guess what
with the rotor in my hands..in the center where the HV plug in ..there was so much garbage ( lack of words here rememeber im french)in the metal that even the needle of my tester could not scratch it off i ve kinda grind it and i now have continuity on both sides of the rotor unfortunatly i have damage the the disk trying to take the rotor off... beheing that i had a really good one i figure i should change it...
but at least i know when is my prob..

 

[thibauja]

Re: merc 850 1977 no fire but passed the switchbox test

ok now... i got the rotor assemblytogeter and put it back on the motor..i was very carefull to put the mark together when i toook to rotor off so i would not have to play with timing,,but looks like i have move the motor or my helper did anyway the arrow on th erotor pully did not aligne with the flyweel dots anymore...so here is where i need help now.. something doesnt sounf right ... i have the arrow and the 3 dots on flyweel lined up then put the belt on and piston no 1 is tdc ( i didnt take the flyweel off) what doesnt sound right is ..why is my rotor in the CAP pointing at piston no 3 wich is not top at all ????
there is a dot and an arrow on the distrib pully and 3 dots in a colun on the flyweel what have to lign up ...
oups i think i just realized ... the rotor i ve installed in MY distrib assembly comes from a 6 cyl and the pully are prob not the sames...im back to the garage will be back...