Re: Need info on '85 Merc 115 & 7.5

Posted by Ed Mc. (67.250.176.24) on January 23, 2004 at 19:06:25:

In Reply to: Need info on '85 Merc 115 & 7.5 posted by beached on January 23, 2004 at 11:02:20:

The exact value isn't as important as the variance between cyl's. Those readings are excellent for motors that are 18 years old. I would change the gear oil, renew the impellers, decarbonize both motors with Seafoam or equiv. carbon cleaner (OMC Engine Tuner, etc), also the timing adjustment suggested is a good idea. Max timing on the big motor should be no more than 21 deg BTDC and this can be checked with a timing light on #1, at full throttle underway. There is a way to check/adjust the timing off the water but you'd be best served by having a good manual in front of you while you're doing it.

The Seloc Merc manual is very comprehensive and well layed-out for both layman and outboard mechanic, and will have lots of good info on repair and maintenance of your big Merc. Try Amazon or eBay as a couple of likely sources for these manuals.

If the little one is running good, other than the P.M.'s mentioned above you shouldn't have to do much else to it. Make sure both motors are lubed at their grease fittings, with a good waterproof marine grease.

Use only Premium in the big Merc; the little one should be fine on regular unleaded. Never use gasohol in either. Use a quality TCW-3 (or better) oil, either mfr's oil or try Penzoil synthetic (seen lots of good comments on it).

It's good to do a decarbonization on the motors once a year, also the mfr's offer fuel additives (such as OMC Carbon-Guard or Yamaha Ring-Free) that promote cleanliness on the innards. Cheap insurance against carbon buildup and they'll help your fuel systems stay clean too.

HTH and enjoy your new jewels!.............ed