87 Octane????

[Evinrookie]

1967 80hp Evinrude
My last few times out on the water my motor runs fine at low speeds (no wake) but when I throttle up to about half way she seems to bog down and starts to surge. My initial suspicion was a dirty carb or air leaking into a fuel line or gas tank. However when I went to my friendly neighborhood boat mechanic for some parts for a different problem, he said it sounded like I'm using 87 Octane (which I am). Is this a problem? I am a first time boat owner and have only been out on my new/old boat a handful of times. The first time I took her out she ran like a champ. Now that I think about it, I did refuel after that first outing.
I trust my mechanic and he's an old school guy specializing in older motors. I had never heard to put high octane in the tanks and want to know if I've found my problem.
Finally, 87 is where I've gone horribly wrong, is there any thing I can do to salvage my 12 gallons of 50:1?
Thanks for any help you can offer.

 

[Evinrude Boater]

Re: 87 Octane????

There's nothing wrong with 87 octane. I usually run 87 or 89 and I've even run 91 and it makes no appreciable difference. I would say you still have some obstruction in the high speed jet. I say jet (singular) because it's surging. The other bank is trying to get going but doesn't have the recipricating power from the starved side. I'll bet the plugs are wet on one side of your engine. The obstruction is in the opposite side.

 

[Evinrookie]

Re: 87 Octane????

Would I be able to verify the "wet plugs" theory in the driveway? The problem occurs at higher throttle levels but I know I can't throttle up that high on the flusher.

 

[Evinrude Boater]

Re: 87 Octane????

Would I be able to verify the "wet plugs" theory in the driveway? The problem occurs at higher throttle levels but I know I can't throttle up that high on the flusher.

Just pull all the plugs and see if there's a difference between banks (port vs. starboard). One jet feeds each bank. If you push the throttle to a point that it's stumbling or surging then one bank is likely getting more gas than the other...or sucking air along the gas line. It sounds exactly like what I experienced a few weeks ago. I posted the thread and figured it out before I received any suggestions. Below is a phot of the obstruction, 3/32". It was stuck in the jet right at the orifice so I took a wire and flicked it out and solved the problem. It'll only take a minute to take out those jets to inspect them.

 

[tashasdaddy]

Re: 87 Octane????

87 octane is just fine. it sounds to me that you have some dirty high speed jets. you have adjustable low speed, but fixed high speed, behind the bowl drain plug.
http://forums.iboats.com/showthread.php?t=244013

 

[Evinrookie]

Re: 87 Octane????

Thanks for all the help guys. If you say 87 is okay then I believe it. Looks like I'm in for a carb rebuild. Thanks for the link TD. What a nasty little bit of crud Boater. Maybe I'll try taking a look behind my high speed jet before I rebuild too!

 

[kenmyfam]

Re: 87 Octane????

87 octane is just fine. Used 89 octane last year as the marina had nothing else and felt no difference whatsoever.

 

[HighTrim]

Re: 87 Octane????

Related reading material

http://www.evinrude.com/en-CA/About.Us/FAQ/Oil.Fuel.htm

 

[Evinrookie]

Re: 87 Octane????

Thanks for all of your help. Very nice link HighTrim. Evinrude Boater, I have yet to mess with the carb. Will I need to remove it to inspect the high speed jets? Now that I have the shifting problem you guys helped me with in another post solved, I will try pulling the plugs to see if one bank is wet. Thanks again for everyone's help with the octane questions.

 

[Evinrude Boater]

Re: 87 Octane????

You can remove the high speed jets through the little access door but take the hood off, it's easier to clean up the drained fuel. It's the two bolts on the front of the carb at the bottom about an inch apart. Have a clean container to catch the fuel when you take the bolts out. Then use a jet removal tool (a.k.a. screwdriver) to remove the jets and have a look through the holes for any foreign material. Hopefully you find the culprit.
Check out my engine videos on Youtube by searching "speedifour".

 

[Evinrookie]

Re: 87 Octane????

OK I still haven't had a chance to pull and rebuild/clean the carbs yet to see if that is my problem. However, I have been reading some recent posts that have put some new ideas in my head. I can't seem to find the exact thread but someone had mentioned a problem with their electric choke and I believe it was TD that explained that they didn't have an electric choke and explained exactly what a choke was. This got me to thinking that I may have been forgetting to open the carbs up completely after starting at half-choke (I have a manual choke). Silly mistake I know, but would this cause the motor to fall on its face when throttling up? If it's not getting enough air to mix with the added fuel at high throttle, I would think the motor might bog down. This will be my next test before pulling the carbs.

Any suggestions??