posted 09-09-2005 09:02 PM ET (US)        

89-Octane Fuel: a mechanic recommended that the engine would run better on 89-Octane fuel instead of the 87-Octane unleaded it normally is fed. The owner's manual says...(87-Octane minimum, I think--I left the book in the boat).

What difference will I get from running higher octane fuel?

posted 09-09-2005 11:57 PM ET (US)            

During periods of idle or trolling, trim the engine up at least half-way so the "heavy ends" of fuel and oil will reaach the recirculation system. If the motor is at a negative trim angle, then nothing reaches the valves and the motor is more prone to "load up".

posted 09-10-2005 01:13 AM ET (US)            

The higher the octane rating, the more resistant a fuel is to pre-detonation.

However, if an engine wasn't designed to need premium, I'm not sure what the advantage of using a higher octane fuel would be. Many people think you get better gas mileage, more horsepower, etc, none of which is true. Mostly it's just marketing.

posted 09-10-2005 02:52 PM ET (US)            

having twins gives me a good comparison to see this slight roughness. I'm pretty good about remembering to alternate which engine I shut down when I am out trolling, and when I turn on the second engine for the run home, it is usually pretty easy to tell which engine has been running at idle for a couple hours.

I always describe it as running "snotty". If it is too rough to really open it up for a few minutes on the run back to the harbor, I make sure to once I an back inside the breakwater. This soon cures any slight roughness or hesitation. At a minimum it is a good excuse to spend a few minutes really letting her rip.

posted 09-12-2005 01:26 PM ET (US)            

Who recommeded that you trim the motor DOWN (negative trim) when you idle?

posted 09-13-2005 09:21 AM ET (US)            

Apparently this feature was re-engineered and dropped from later models. My mechanic has mentioned it as a possible upgrade on my engine.

posted 09-13-2005 04:41 PM ET (US)            

It turned out after having my local OMC (Bombardier) dealer research my condition, that while it never turned up in a written service bulletin, the factory had instructed shops that called in with owners of these motor complaing about rough idling, to disconnect this system, plug the hose coming from the valve, and replace the thermostats, diaphragms and ported thermostat covers with simple vernatherms, no diaphragm, and simple unported thermostat covers from V-4 models. The notion that was explained to me was that the system (that I think Jim is calling "Power Cooling") cooled the power head too much at idle, and the motor needed to run hotter at idle in order to run smoothly.

Jim, if the information I got from my dealer is correct, the motor runs hotter at idle *without* the Power Cooling system connected, so either it sometimes didn't work like it was supposed to, or there was *more* cooling provided at idle rather than less. I can tell you that now I have a temperature gauge and can read what is going on back there, my heads are running at 160° to 170° at idle when warmed up, and they drop back down to about 140° when I speed up.

posted 09-13-2005 08:23 PM ET (US)            

I am ambivalent about the higher octane. Sometimes at marina docks you have to buy 89-Octane or mid-grade, so I do run it on occasion. Generally I fill the boat's tank with 87-Octane.

On the effect of trim angle on low speed running and subsequent stumbling when accelerating, I ran the boat this weekend for a hour or more with an eye to keeping the motor trimmed close to level. It seemed to run well, and I did not have any noticeable hesitation or stumble when accelerating back to planing speeds.

On the elimination of the Power Cooling feature, I am still a bit confused about the effect of removing it on engine temperature at idle. I will double check with my OMC expert David Zammitt at Lockeman's and see what he has to say. In either case, it looks like a not too expensive way to improve the engine. As mentioned above, if the factory decided to take this Power Cooling feature out of the engine, they probably had a good reason for doing so.

Now, to add a new idea the quest for more performance, I just came across this interesting discussion:

http://bbcboards.zeroforum.com/zerothread?id=63164

wherein a recommendation is given (by SEAHORSE) to replace a particular fitting in the cooling system in order to increase the effectiveness of the cooling for the electronic voltage regulator. Having just spent $235 (and more for labor) to replace the electronic voltage regulator in my motor, and having performed a dissection of the old unit which clearly showed signs of overheating as the cause of failure, it sounds like this minor part change might be a good idea to avoid future failures of this expensive part. Again, it seems like a few years into production of this model engine the OMC engineers came up with some small improvements which might help performance.

The new nipple fitting is about $4 and the replacement seal is $2.97.

Part numbers are 344202 for the nipple and 335981 for the seal.

posted 09-13-2005 08:46 PM ET (US)            

Over the course of the ten seasons I owned that motor I did, at times, run it on 89 octane fuel and "Premium" fuel thinking it might be good for it.

It made absolutely no difference in how that motor ran. That motor was so reliable and consistent I was left with the impression that motor would run on cooking oil!

posted 09-13-2005 09:16 PM ET (US)            

I don't know how much better your particular engine will run with mid-grade (89 octane). It may run much better and may not. I think that depends on your compression ratio and the timing specs for your engine. It was fairly common in the post-1960's era for auto manufacturers to lower compression ratios and timing specs so cars could run on lower octane, unleaded gas. This is of course due to the fact that older engine designs (pre-1970's) had higher compression ratios, more timing advance (generally) and could not run well on low octane unleaded fuel.

My guess is that if you have a compression ratio of more than 10.1:1 your engine could indeed run "better" with 89 (or higher) octane. That could lead this thread all over the place however as "better" is a relative word in this situation. If your engine knocks at all now, it will be reduced (or eliminated) with the higher octane gas. If it does not knock currently and runs fine, you likely will feel no performance difference at all - but your combustion chambers and other engine internals may remain a bit "cleaner". Its hard to generalize in your specific situation so why not simply test the higher octane out to see?

posted 10-06-2005 08:41 AM ET (US)            

In one stretch we were in some shallow water and had been running at idle with the engine trimmed up (to reduce draft). Acceleration back to planing speed was accompanied by some stumbling in the engine.

On the next slow speed stretch, I made a point to set the engine trim as level as possible. After a couple of miles at idle, the engine accelerated to planing speed without as much complaining.

posted 10-06-2005 09:21 AM ET (US)            

I'm not wild about paying for premium grade gas but the warranty, still in force, says "PREMIUM GRADE FUEL MUST BE USED OR THE WARRANTY WILL BE VOIDED."

I have also noticed the stumbling and hard starting with the engine tilted up for shallow water running and just figured the carburetor bowl was not being level and filled.

posted 10-08-2005 08:25 PM ET (US)            

I recently heard this anecdote regarding de-carb: a fellow bought a can of decarb instead of fogging oil by mistake. He fogged his motor for winter storage with decarb solvent. In the spring his engine was destroyed--the solvent had ruined the pistons and cylinders.

posted 10-18-2005 03:15 PM ET (US)            

There are a number of de-carboning agents that have been on the market for some time. Personally I prefer to use OMC/Bombardier products on my 225 looper, as it is an OMC motor. I used to give it a dose of de-carbonizer (my term) once or twice a year, but now at the insistence of my local OMC/Bombardier mechanic, and in agreement with a number of fellow boaters whose opinions I value, I religiously use the OMC/Bombardier de-carboning fuel additive, the result of which, according to my mechanic, keeps my motor just as carbon-free as the occasional shock treatment. I understand a similar but more expensive method is to use the OMC/Bombardier 2-stroke oil that has the decarboning (and other) additives in it.

posted 10-18-2005 08:47 PM ET (US)            

For those of you who are dying to know about it, just google for the phrase

"Modified by Dunk at 6:19 PM 8/1/2003"

posted 10-19-2005 08:39 AM ET (US)            

I hope this question comes out sounding as it is intended; a respectful but legitimate curiosity about what I thought I understood about two cycle engines, that doesn't square with your last comment.

If all the fuel is burned before it gets to the rings (so the fuel presumably can't carry any anti-carbon agent to them), how do the rings get lubricated?

posted 10-20-2005 09:22 AM ET (US)            

So it sounds to me like the recommended procedure is to continue with the Carbon Guard fuel supplement, but to add an occasional shock treatment?