merc 850 1977 no fire but passed the switchbox test

[thibauja]

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

nop just check the parts number and they are the same ..
now i m really confused

 

[thibauja]

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

back to square one... ok lets forget about rotor pointing to piston 3 that was a silly mistake... finaly got every thing back together timing looks ok but
SAME ^!$@^#$% problem spark when switch on an when i let go the key switch NO SPARK while turning any cylinder
the DI box past the test gives a spark every time, th ebatery is FULLY charges 12.9 V , the rotor disk is NEW , the rotor i almost new and the mercury switch is disconnected.
any sugestion ?
im seriously considering sell the motor for parts..
thanks

JT

 

[ricksrster]

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

Could be a bad key switch.

 

[thibauja]

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

been there done that LOL
my keyswitch is bypass red and white twisted together and yellow to start it
the bypass is good i get 12V on hte red AND on the with on the switchbox..
here is an other test i just did a minute ago...
the baterry is abov 12V but when its turns on starter the power on the white wire of the switchbox drop down to 9Vsomething wich is probably not anough and would explain why i only get a spark when i let go the switch ..could it be ??
JT

 

[thibauja]

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

this site is a great toolbox... here is what i found from this link http://www.outboardparts.com/mercury/troubleshooting/printguide.htm
im replying ot myself caus it might help someone else :
and thanks to whoever put this link as a ref in a post its a realy good reading

Dead or no fire until you release the key switch:
Disconnect the mercury switch and reset, if the engine fires, replace the mercury switch. Check the voltage on the red and white ignition wires at the CD unit. If the voltage is less than 9 1/2 volts during cranking there is a problem in the battery s or the ignition switch box.

im back to reading my meeter and try and other battry
JT

 

[billybones]

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

No amps in battery. lower the draw by turning off everything while turning off switch, get a spark. A fully charged battery should get 2.2volts per cell times 6. minimum. Easy test is to put meter on volts put across battery terminals turn key should be a tiny amount af voltage loss. Amps push voltage. No amps no voltage. or a short somewhere eating up amps. in a car we would open up the door and turn the key, If the dome light goes out and no start, bad battery. dome light stays lit. bad starter. Just a fyi. In a car if you put your meter on the battery after starting you should get more volts after starting than alone. 13.5 for a good alternator. Any less your alternator is not working properly or voltage regulator. now a days it is an all in one deal. sorry for the long post. just a lot of people do not know these things. Edit: Old wires and bad ground connections will do the same thing. Clean and tight especially on boats.

 

[thibauja]

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

here i am again...
switch box ok.. 12 V and 9.5v on the switch box while crinking, all ground connected tite
switch key by passed (red and white jumped) mercury switch disconnected and still the same prob only one spark when i let go the key ... so i tryed to test the trigger this way. using the test of the switchbox with HV wire from the coil at 1/8 of frame.. but insted of jumping the triger wires to get a spark (by the way this works)i turned the motor tu have the rotor disc to trig the trigger i shoudl get a spark right ? I DONT so i guess i should suspect the trigger so now the question is how can i test this trigger with a digital V meeter ? or is there an other way to test it ?
thank you to all
Jack

 

[tramp666]

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

I have been trying to following you on this and I had a similar problem I had to work through. Believe me it's work. Don't give up! You will get it. I will offer this one piece of info that fixed mine. Take off the distributor cap and clean the carbon spring loaded center post with WD 40 or electrical cleaner so it will spring freely. It fixed mine. Made contact with the rotor and vola! spark to the spark plugs.

good luck!

 

[thibauja]

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

i will do that ..at this point i l try anything ..
but dont put to much hope in it cause if i recall when i manualy aim the rotor to a plug wire , disconnect de distrib wires ..put the cap back on and jumped the 2 connector on the switchbox to smimulate the trigger s job i was getting a spark on the plug..
but i will redo this test i im not sure of anything anumore ...i ve tested every thing so many times.. but aparently this test is not exactly as cranking with the starter cause teh switchbox may not have a minimum of 9.5v while the starter is cranking it ...
thanks for the info i will try it any way... and if it works ...i will bang my head on a wall for an hour.
JT

 

[Clams Canino]

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

You're better off just snagging a used distributor on Ebay.

-W

 

[thibauja]

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

well i did almost that i rebuild my distrib with a used 6 cyl distrib being that the rotor and the distrib assembly was the same number the diff was the rotor disc inside was for a 6 cyl end result i brook the trigger on the new kit trying to remove the disk so i had to used my old assembly and probably kept my problem...
but i agree with the idea.. its the obvious next step :-(
but i was wandering if anyone knew a way to test the trigger before i put MORE $ in there
JAck

 

[thibauja]

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

only spark when i let go the key switch but not while cranking
it was the trigger in the distrib... :-(
i found a way to test the trigger...
BUY an other one and try it...actually with the new second hand distrib in my hands timing belt removed and distrib wires connected to switchbox ...
key switch ON an the HV wire from the coil at 3/8 of the ground ...when you spin the rotor maualy it sparks .... it s THE way i found to test the trigger
thats the end on this ...
Jack