115 Yamaha running rough
 

My 1998 115 Yamaha has been bullet proof and hasn't failed me once yet although I'm the second owner and have only owned it for the last five years. It has just recently started running rough/shaking but ONLY does this between 1000 and 1200 RPM. and anything above or below that it runs perfectly fine and smooth. Had Bass Pro mechanic look at it and do a 34 point inspection but couldn't figure out what is causing it to shake. They removed, disassembled and cleaned the carbs, removed and inspected the reed plates, did a compression test 120 across all four cylinders and suggested I change the fuel pump due to a suspected weak diaphragm , which I have done. They switched carbs around as well as the coils to see if symptom persisted and it did. Told me they had 13 hours into diagnoses but only charged me $450 for four hours.
I don't know about the previous owner but I only run non ethanol fuel and religiously add ring free.
Has anyone experienced similar issues or can offer some advice/suggestions, I just don't want to bounce around from one mechanic to another throwing money away and not find out what the problem is.

Rough Running Yammie
 

Hi. Check around, maybe there is a site for Yamahas similar to the ETEC owners site where one can ask questions and get some good advice. The ETEC site includes regular moderators who either work for BRP or are affiliated in some way and can provide good advice because they get exposed to more information than an individual does- maybe you'll get the same from CSC. The ETEC site requests engine model and serial number in addition to the problem summary. They can advise on service bulletins and sometimes if your engine has received a repair for a bulletin, latest software, etc. .

Does the shaking happen in idle too, or just in gear?

Have you checked the prop? Looseness or slop in the hub, or even imbalance might cause such a thing.

I think you still have a carb problem - rpms where you are having problems are transition from low speed to high speed circuits. Figure out which cylinder is dropping out and go from there.

The mechanic at Bass Pro did say that when he removes the spark plug lead from #4 cylinder, it does not cut out as much as on other cylinders.

I don't believe it does it in idle or at least if it does, its not as noticeable. I'll
check the next time I splash the boat.

I agree. I think you have a lean misfire problem. Outboard carbs are very simple devices, especially the idle and main jet circuits, but the transition between the two systems is pretty sensitive and a little bit of dirt in the idle circuit is all it takes to create your problem. I've been able to create exactly your problem on my old 'Cuda 340 4 barrel Carter AVS carb by adjusting the idle mixture screws too lean, which causes the carb to get VERY lean during the transition stage. Or a slight air leak at a gasket might cause the same problem, where both the idle and main circuits are rich enough to mask a slight air leak, but not during the transition stage.

If your motor is like my old V-4 Evinrude, it will have two 2-barrel carbs, one barrel to feed each cylinder. If you can do a cylinder drop test at 1000-1200 rpm(short out the ignition on individual cylinders; if no rpm drop on one cylinder, that's the one with the problem!) you can narrow it down to which carb needs attention. A quick fix, IF your motor has idle mixture adjustment screws (many just have fixed jets) would be to just richen up the idle mixture on the problem cylinder. But the problem carb really needs a good cleaning.

Personally, I think the old carb motors are so simple and easy to work on that it's hard to justify paying someone $100/hr to do anything on them that doesn't require special tools or the acetylene wrench, so you can save yourself big $ by getting a factory service manual and learning to do your own work! And the ability to diagnose and fix your own motor when you get out in the boonies with no experts around is priceless!

Thanks for the input Bushwacker. The mechanic did say he switched the carbs around and the issue still persisted so if it is the barrel that feeds the #4 cylinder, wouldn't there be a noticeable difference when he switched the carbs ? BTW, I did purchase a shop manual for the motor however educating myself in the subject is going to take a very long time.

The miss would just follow the carb around if you switched it - so no noticeable difference.

That makes sense. When you guys talk about low and high speed circuits, am I right to assume you mean fuel flow circuits as opposed to electrical circuits ?

Yes - fuel - carbs have idle circuits and high speed jets.

Thanks for clarifying, when I see the word circuits my brain automatically thinks electricity.

Put the boat in this afternoon and did Dunk's decarb procedure with a 16 oz. can of seafoam mixed with 3/4 gallon of fuel and 3 oz. of Yamalube. Issue still persists, checked prop and hub, all seems OK. I did notice that the rough idle only seems to occur when it's in gear and under load, not saying that it's not missing at all in neutral but if it is, its not obvious enough for me to notice. Seems like the vibration is gradually getting worse or more pronounced.

Warm the motor up and run it for 15 seconds at the rpm that it misses at (5 seconds for a high rpm mis)then shut it off without moving the throttle. Pull all the spark plugs as quickly as possible noting what cylinder they belong to. Look at the electrode on each plug, noting coloration and wetness. 1 should be slightly different. If 1 plug is drier than the others, its a fuel issue on that cylinder. If 1 is wetter than the others, it's an ignition issue on that cylinder. A lighter color is a fuel issue, a darker color is ignition.

Plugs should be "read" as the first step in troubleshooting a misfire. The method above works most of the time. The motor should be under load, so it needs to be ran in the water or in a tank. Hopes this helps.

That's because it takes more fuel/power to spin the prop in gear than it does to just overcome friction in the system in neutral, so if one cylinder is lean, it will be more obvious when it's under load. Red's idea of reading the plugs MIGHT reveal the suspect cylinder if you do it under load. But to fix it you're gonna have to disassemble the offending carb, soak it overnight in some strong carb cleaner, and then blow out all the passages with some compressed air. Snake oil ain't gonna fix it!

Oops, double post!

I mentioned in my original post that the technition at Bass Pro pulled the carbs disassembled and cleaned them last fall. Having said that while visiting Harkers IslandI last fall I brought up the issue with a Yamaha dealer while buying Yamalube and he stated that the holes in the small jets are so tiny, sometimes cleaning them just won't cut it and they may need replacing.

You may be able to unplug them with small wires. I once had a car with a 2 barrel Holley, and the idle air bleeds on top of the carb were so small that about every 6 weeks I had to spray the top of the carb with Gumout to get it to idle smoothly! Finally changed manifold and installed a 4 barrel Carter Thermoquad and eliminated the problem while also improving gas mileage and power! The racers love Holleys but I've found them to be pretty temperamental for daily street use.

I've been watching thread with interest to see what could be found wrong. I guess I missed the part that you said it was worked on last fall, we are coming up on this fall now(might need to go over everything that was done last year again). I got so disgusted with my 2001 Yamaha 225 with several different mechanics unable to find problem, I traded it in.

Here's my 2 cents:
For $27 each (4 total required)

Change the idle speed jets.
Change the idle speed jets.

It's really frustrating when you pay someone $100/ hr. and they neglect to make such simple suggestion to change out the jets. When you're not familiar with outboards or mechanically inclined, unfortunately you're at their mercy ! Took the boat to a highly recommended mechanic two hours away and had the motor worked on. Was told #4 cylinder was not supplying power and removed carbs and cleaned in ultrasonic cleaner for two hours ( never suggested or recommend to replace jets ) Also balanced carb plates. Brought the boat home but didn't get a chance to test it due to thunderstorms.
Found out the alarm buzzer is missing and was told it's part of the ignition switch so the switch would need be replaced and that a replacement buzzer is not sold separately.
Any recommendations as to what I can use to replace just the buzzer without having to dish out another $150 for a switch assembly that doesn't necessarily need to be replaced except for the missing buzzer ?

When you said you had it worked on by a Bass Pro mechanic and he claimed 13 hours into it, first assumption would be this baby should run like a champ. I guess when he cleaned the carb, he wiped a little varnish off... At the risk of offending some of our forum's mechanics, I think I'd run down and negotiate some type of refund, if un-cooperative, report to BBB and YELP of his incompetence.

Driving 2 hours to see a competent mechanic is nuts...
Hope your problem is fixed.