90 hp merc feels like its droping a cylinder HELP PLEAse

[jake69442]

MY 1985 mercury feels like its droping a cylinder after running @ about 1800 rpm for a whyle, when i open to wide open throttle after running at lower rpm it seems to clear up some times and you can definetly feel when the last cylinder picks up and motor has the power it should. but it does not allways clear up. i pulled the plugs for inspection and the bottom cylinder is completly dry and clean as a whistle whyle the other 5 look the same and have some fuel residue on them... please please any help would be appreciated....

 

[sschefer]

Re: 90 hp merc feels like its droping a cylinder HELP PLEAse

A completely clean cylinder? Do you mean that the top of the piston is clean, (no carbon)? Or, is it just the plug that is dry?

 

[jake69442]

Re: 90 hp merc feels like its droping a cylinder HELP PLEAse

the plug is dry cant see in to the cylinder,, just did a compresion test and all cylinders are close to 145 to 150 illegedly theres a new power head on motor. i dont have spark in cylinder 6 and had only very little spark in cylinder 3 and no spark in cylinder 4

 

[jake69442]

Re: 90 hp merc feels like its droping a cylinder HELP PLEAse

i also did an ohm test on the coils and all are within specs according to the service manual. should all the coils fire when cranking the motor over with the plugs removed ??

 

[kMunster]

Re: 90 hp merc feels like its droping a cylinder HELP PLEAse

Start by checking your stator before you blow your CDI boxes, Are you operating under high outside temps. Heat causes problems remove insulation belt from engine cover. Stator problems will very under heat and load. Not output water temp.

 

[sschefer]

Re: 90 hp merc feels like its droping a cylinder HELP PLEAse

I believe that the switch boxes are 1,3,5 and 2, 4, 6, (check your manual). Weak spark on 3, no spark on 4 and 6 would lead me away from a switchbox or coil problem and to a failing stator as was previously stated. According to gospel, if the stator tests bad with a DVA then change it and the trigger too. If it doesn't check bad but you still suspect it then pull the flywheel and look for burn marks on the stator. The last step is a recommended step in the full test process.

 

[jake69442]

Re: 90 hp merc feels like its droping a cylinder HELP PLEAse

I will check it when i get home from work,, should all cylinders have spark when cranking or should it be checked whyle running also what might be the problem with the bottom plug being dry and clean they are a brand new set of plugd w/ maybe 5 hours on them there is some evidence of the plug firing but no carbon or fuel residue on plug

 

[jake69442]

Re: 90 hp stator test bad any thing else i should order

Re: 90 hp stator test bad any thing else i should order

ok the stator tests out of range per service manual is there any thing else i should order with it perhaps the ignitor and maybe a switch box or 2,, im not looking to spend extra money foolishly but i have my daughters for the week and realy dont want to dissapoint them..i tried to get a stator locally and cant for a week not cool any ideas i realy want to get this going again in a day or 2 the serial # is 6623264 any help would be greatly appreciated

Thank you much

 

[jmburock]

Re: 90 hp merc feels like its droping a cylinder HELP PLEAse

Best thing I ever did was replace all my ignition components with CDI Rapair parts 2 summers ago. Replaced stator, switch box, regulator and trigger. No more starting or running problems and reliability has increased dramatically. Pre-emptive maintenance will save you so many headaches during the boating season, which is all too short here in New England. Highly rec. CDI instead of OEM merc. ignition components, although Merc. is certainly better than Sierra.

 

[jake69442]

Re: 90 hp merc feels like its droping a cylinder HELP PLEAse

where can i find cdi parts

 

[sschefer]

Re: 90 hp merc feels like its droping a cylinder HELP PLEAse

where can i find cdi parts

http://www.iboats.com/Mercury_Stators/dm/*******.663435571--**********.059205460--view_id.271562.

 

[jake69442]

Re: 90 hp merc feels like its droping a cylinder HELP PLEAse

changed the stator and trigger and got great spark on all cylinders and starts right up but still ran a little rough at mid rpm,, changed switch boxes and it runs great now even smooth at lower rpms and doesnt load up with fuel either

thanks for all the help