75hp merc no spark on 3-4

[horsefly38425]

it is a 75 hp ser 6613843 don't know the yr but has a good spark on 1-2 nothing on 3-4. I moved the wires from #1 to all 4 coils and they spark good. what should i ck next

 

[ricksrster]

Re: 75hp merc no spark on 3-4

Are you saying you have power from all four coils but plugs 3 & 4 don't fire?

 

[ricksrster]

Re: 75hp merc no spark on 3-4

Your year is 1985

 

[Laddies]

Re: 75hp merc no spark on 3-4

OHM test your stator sounds like one side is gone

 

[horsefly38425]

Re: 75hp merc no spark on 3-4

i guess what i should have said is there is no spark from any coil if i hook it two the primary wires that power #3 or #4 but any of the 4 coils when hooked to primary wires for #1 or #2 spark is good. I ck'd the plug wires frist they are good then coils all4 ck good, I thought it maybe was the power pack ,but i will pull flywheel and ck stator. It looks like some of the wires under flywheel are cracked. how do you ck stator

 

[ricksrster]

Re: 75hp merc no spark on 3-4

Ok, here is the resistances you should have for stator. disconnect the the blue and Blue/white from the switch box. measurethe resistance between these two wires. It shoild be 5800 - 7000 Ohms. Blue to ground should have no contitnuiuty. Now do the same with the red and red/white. you should have 135 - 165 Ohms. No continuiuty between red and ground.<br />Disconnect brown and white/black trigger wires. connect Ohm meter to these two wires and you should have 800 - 1400 Ohms. do the same with white and purple. Yoshould have the same 800 - 1400 Ohms.

 

[Laddies]

Re: 75hp merc no spark on 3-4

horsefly, if you don't have a OHM meter you can change the red and red/white, the blue and blue/white wires on the switch box to see if half the stator is bad, just a alternate way to ck. good luck

 

[horsefly38425]

Re: 75hp merc no spark on 3-4

ohm meter is in tool box at work,so i moved the wires and had fire on all 4 swicthed wires back to the right place no fire. pulled flywheel & stator and found the 2 longer wires that go to the small box in rear of swicth box were in bad shape.I thought they were charging sys / they have been hot insl. is cracked. fixed them . Then found the white wire from trigger was bad. fixed it too. Now it starts but if you try to idle it she dies below 1500r's At higher r's seams to run ok /yes i have ck carbs & pump. found a new stator if you think this one is weak or do they go out all at once? can't find a trigger on here for this motor? At least it does start now thats better than it was

 

[Laddies]

Re: 75hp merc no spark on 3-4

Sounds like the low speed windings in the stator are bad, alot of times you can repair cracked insulation with liquad tape

 

[horsefly38425]

Re: 75hp merc no spark on 3-4

this think is driving me nuts I got it running found wire from trigger was broke inside insulation.Starts/runs great on muffs. ck'd timing 4deg at start set carb air at 2 out all looked good. Went to the river,more trouble now. It will not power up when it hits 4000 it just starts to bog down. comes out of the hole just great.so i move timing both ways and went in/out with air still stator ck'd OK could it be shuting down at this rpm.I don't know of a way to ck it at high rpm. And i hate to buy a new one if it sound like somthing else. I'm going fishing and leave this up to the experts for a while

 

[ricksrster]

Re: 75hp merc no spark on 3-4

Did it ever go over 4000 RPM in water? you could try trimming the motor up a little or go down in pitch.

 

[horsefly38425]

Re: 75hp merc no spark on 3-4

no trim on motor,but i don't see as that would help why would i need to change picth it would turn 5500+ before this problem came up, it just starts too miss at 4000 and will not pick-up no matter how far forward you push thottle as if it was running on 2 or 3 cyl. agin. we/my daughter has had it 4yrs.I put a fuel pump dia. in it last yr / it's ran fine till now

 

[ricksrster]

Re: 75hp merc no spark on 3-4

Time to check stator and tigger resitances. Disconnect red and red/white wires from switch box. Connect Ohm meter lweads to these two wires. Resistance should read 135 - 165 Ohms. Red to ground no continuity. disconnect blue and blue/white. check resistance at these two wires Should be 5800 - 7000 Ohms. Trigger White/black to brown and white to purple 800 - 1400 Ohms. Coils are primary should be 02 - 1.0 Ohms, secondary 800 -1100 Ohms.

 

[horsefly38425]

Re: 75hp merc no spark on 3-4

got my meter and ck'd blue/blue-white 1200-1300. every thing else ck'd OK. I will order it now

 

[horsefly38425]

Re: 75hp merc no spark on 3-4

got new stator on now problems have gotten worse. won't idle/r's not stable. backfires /quits. when it does idle it's rough /misses. O.K. carbs are clean/pump is good,but bottom carb if i move the air,rich-lean seams to have no effect. top carb, if i move it i can tell it is working right. timeing 4deg atdc at start- is that right/ max 27deg btdc. is that right [sticker is gone] i set with a light. what should it be at 1000/r's idle. My kids boat, she don't have $$$$ to replace everything that could be wrong. i need to isolate this problem need to add it does have a good spark on all 4 it will trigger my timing light. have 120-125 psi on all 4