79 Evinrude 15 Manual
Re: 1979 15hp evinrude motor Bob; I'll throw this out there for your consideration. I have the same make and HP motor as you do, about the same age too. Bought it used, looked like it was in fair condition but. Using OMC's 50:1 oil w/ 87 octane fuel (has ethanol) I noticed an oily residue draining from the exhaust hub after the motor sat for 2 days or so.
I had been using the recommended heat range sparkplug also which is a 9 heat range like a QL77??? At the beginning of last year (12 months after buying the motor) I was going to put in new plugs (as I do a lot of trolling) and mentioned the excess oil from the exhaust hub to the mechanic. He said: 'we see that quite often on those older motors. If you switch to the 100:1 OMC use a #8 heat range plug and only burn 91 octane fuel (ethanol free)it's a much cleaner burn and the excess oil will almost stop. One word of caution is that you MUST fog the engine prior to winter storage!! There's no rust preventative in the OMC 100:1.'
My motor run much better and he was right about putting a stop to the excess oil. Keep in mind, my motor probably has never had new rings put in which I'm sure aggrevates the problem. Re: 1979 15hp evinrude motor Joe is again correct. You could use a synthetic blend oil to help reduce the oil residue, but IMHO it's a waste of money. I troll (VERY slow) w/my 15hp exclusively, and have the same oil/gunk build-up in the prop that you mention. No other bad symptoms at all.
1990 Evinrude Manual
I do a decarb yearly, and I highly recommend it for those 9.9/15hp motors, trolling or not. I read somewhere that the piston skirts in these motors seem to build up carbon over time until failure. I don't want to find out if that's true! Just search 'decarb' in this forum. The 100/1 fuel/oil mixture was a OMC disaster resulting in more blown powerheads then I care to mention. I strongly suggest that you DO NOT use that mixture but rather stick to the 50/1 mixture I recommended in my previous reply. I surmise that other members might be juumping in here shortly with their views of what mixture to use.Joe; I would never reply to a thread with information if I knew for certain that the info I was posting was potentially harmful; so if am wrong I sincerely apologize!!
50 Hp Evinrude Manual
On the other hand, I wonder why OMC continues to market 100:1 oil? My immediate thoughts are that OMC MAY HAVE HAD many engines blow because the 100:1 mix does NOT have rust inhibators. Subsequently engines spit rods because the owners didn't fog the engine prior to winter storage; or engines with oil injection were designed to use a 50:1 mix oil and a 100:1 mix creates the failures. OMC's failure rate didn't coincide with their FICHT injection did it? The mechanic that I spoke with did say that engines were failing; but it was because owners were fogging the engines and as a result, OMC recommends a 50:1 mix. I'm not trying to start a heated debate but rather asking a question. Why would OMC continue to market the 100:1 mix?
The residue in my exhaust housing was substantial!! Clearly not a clean burn. I have worked for 2 major rec. Vehicle manufacturers in a service tech capacity (dealer service training and the other was a snowmobile race team) and have a fair amount of experience with 2 cycle engines.
1979 Evinrude 15 Hp Manual
For the life of me; when I saw all of the unburned residue in the exhaust hsg, I knew that wasn't anywhere near right. As I said; if you chose to mix 100:1; the engine does require fogging before storage. So my second question would be; have you gotten info from OMC that is contrary to the info that I got from the service tech guy I spoke with at the dealership? If I'm wrong, I'll immediately dive on my sword and beg for forgiveness!