Highest octane, is it critical??

[Incaboater]

I am going to flush the old gas out of my tank and my carbs. I have that clymer manual (is that what its called?) and it said that the highest octane is recommended. I couldn't pull up to the gas station and just put the cheapest stuff in? Does it have to be the highest octane they sell? The engine is an 1981 70hp johnson in line 3 cylinder. Also is there a better manual, I don't like the way this manual covers a wide array of motors.

 

[fireman57]

Re: Highest octane, is it critical??

The consensus from the pros here is that these engines were made to run on 87 and you are wasting your money if you go any higher. It could even lead to predetonation which is not good. I would stay with 87 and make sure it is tuned properly. An OEM manual is your best bet as it has much better procedures in it plus tips on how to do things.

 

[tashasdaddy]

Re: Highest octane, is it critical??

here's manual info, you can by this or watch ebay for one.

 

[F_R]

Re: Highest octane, is it critical??

A word of caution to those that may be reading this and have older motors. There were some OMC motors back in the early '70s that did require premium high octane gas. Yes, even leaded! Putting low octane gas in those motors caused pre-ignition and detonation and piston failure. Boy, was that technology at the wrong time or what?

Even on today's engines, the higher octane gasolines are to prevent pre-ignition and detonation in those that require it. There is no advantage in those that do not need it. But it won't harm those that don't need it either, just a waste of money and natural resources.

 

[Incaboater]

Re: Highest octane, is it critical??

here's manual info, you can by this or watch ebay for one.

Thanks for all the info guys, I just need the link to that oem manual that is missing from the above post and I will be set.

Thanks again

 

[Incaboater]

Re: Highest octane, is it critical??

Ok, I found your link to the manual in another post. My question is should I get the owners manual or the service manual?? Which would be the best for wrenching on the motor?

 

[ezeke]

Re: Highest octane, is it critical??

Buy the service manual, because it contains everthing in the owner's manual. Try Ebay before you buy from the vendor They sometimes sell for 1/4 the price of new.

http://cgi.ebay.com/ebaymotors/1981...453QQitemZ260039401695QQrdZ1QQsspagenameZWD1V

 

[F_R]

Re: Highest octane, is it critical??

The owner's manual tells you how to start and run it, and where to grease it. Stuff like that. It won't tell you a thing about how to fix it. On the other hand, the service manual is very complete on how to fix it, but actually does not mention some of the basic stuff that is found in the owner's manual. I guess they figure if you are digging into the innards you already know how to run it.

 

[ezeke]

Re: Highest octane, is it critical??

Back to the question on fuel grade:

http://www.evinrude.com/en-US/About.Us/FAQ/Oil.Fuel.htm#Q4

 

[Dhadley]

Re: Highest octane, is it critical??

If that motor has not been modified it requires no more than 87 octane. In fact higher octane could be detramental under certain circumstances. If the head has been cut or the powerhead modified in some way then it may require more octane.

 

[F_R]

Re: Highest octane, is it critical??

Aha! The Evinrude thread explains why we had so much carbon and ring-sticking trouble back in the TC-W2 days.

On the other hand, it is obvious that the BRP engineers don't remember the OMC old hi-compression, high horsepower-for-size-motors of the '70s and all the service bulletins that came out telling us how to de-tune them to keep them from detonating under the lead-free mandates. Man, I wish I still had those old bulletins!