77 merc 500 missing on 2 cylinders

[greasemonkeyjmj]

i have a 77 merc 500 that sat for 16 years. the previous owner said it wouls start but had no power, he blamed it on old gas and had carbs rebuilt. well he didnt change the old gas and ran it, the first time out it was doing good then lost power like before, so he parked it, blaming it on the carbs again. i bought it, replaced impellor, went through the carbs, which were spotledd and took it out it ran good for about 20 minutes, then it cut out for a split second, a few seconds later it did it again, but this time is went down to a idle. after about 15 seconds it pick up and ran right for about 5 minutes and died out again and never would pick back up. when i got to the bank i checked and cylinders 3 and 4 are not getting a spark. any guesses on what it could be. i dunno if it is affecting it or not, but the top crank seal is leaking pretty bad, i dont know if it may have fuel mix on something that it shouldnt have. thanks

 

[Laddies]

Re: 77 merc 500 missing on 2 cylinders

It sounds like a stator failure but could be other problem in the ign system. A simple way to tell if it's the stator is while it's losing spark on the bottom 2 cyls. swap the red and red/white and the blue and the blue/white wires at the switch box if the problem goes to the top cyls is the stator. The trigger can be checked the same way by swapping the top 2 trigger wires with the bottom 2.

 

[greasemonkeyjmj]

Re: 77 merc 500 missing on 2 cylinders

well i went out to swap the wires around and see what i got. but the problem is, i guees since the electronics cooled down, that it is firing on all 4 cylinders again. i would put it back in the water but it is 30 miles back to the river. so i think i will run it on the muffs and see if it will heat up and start to miss again

 

[Laddies]

Re: 77 merc 500 missing on 2 cylinders

If you know anyone with a DVA. we have test data for them or a OHM meter the OHM tests are not very accurate but the DVA will usually pick up the problem.

 

[greasemonkeyjmj]

Re: 77 merc 500 missing on 2 cylinders

It sounds like a stator failure but could be other problem in the ign system. A simple way to tell if it's the stator is while it's losing spark on the bottom 2 cyls. swap the red and red/white and the blue and the blue/white wires at the switch box if the problem goes to the top cyls is the stator. The trigger can be checked the same way by swapping the top 2 trigger wires with the bottom 2.

ok i let it run for about 10 minutes and it dropped the bottom 2 cylinders out, so i swapped the stator wires around and it started getting spark to the 2 dead plugs. looks like i need to order a new stator, huh ? i was also thinking, that on some motor, when the stator goes bad that the tach doesnt work. is this correct ? mine had been working, but i notice when i had it running on the muffs, that the tach was only show around 150 rpm.

 

[Laddies]

Re: 77 merc 500 missing on 2 cylinders

Your stator is bad if the spark problem moved, the tach works off the battery windings in the stator not the ign. windings

 

[greasemonkeyjmj]

Re: 77 merc 500 missing on 2 cylinders

thanks for the help on this problem.ill order me a new stator and see what happens. i called the previous owner earlier this afternoon, and from what he described , this is the same symptoms the engine had 16 years ago when he parked it, thinking it was carb problems. i guess while i have the flywheel off, i might as well see if i can fix my fuel leak around the crank. thanks again