Yamaha 115 2-stroke ?'s

[johnnycomelately]

First off, hello to all this site is a wonderful resource! Here is my issue:

We have a 2002 Yamaha 2 stroke with dual carbs and 330 hrs on a Parker 1801 that has me perplexed. The engine starts fine, idles fine, and runs perfectly smooth except when we first put it in gear. At about 1100 RPM it runs rough. Its almost as if its missing a beat and causes it to vibrate the entire motor. It responds to throttle adjustments as it should and every other RPM range is as smooth as glass. We have changed the plugs, fuel filter/seperator, put new fuel in it, and checked the fuel vent. I had Morehead Marine water test it and they reported it ran fine, but I didn't tell them the problem was specifically at 1100. Is this normal for this motor and should I take it back for another water test with the specific range it vibrates? Thanks in advance for all the help.

Johnny

 

[Outta Here]

Welcome!

I had a Yamaha 115 on an 18' Parker. Great boat and motor.

Although I cannot address your problem directly, maybe this will help.

Only a couple of months after a carb re-build, I tried some 99 cent Walmart carb cleaner (same as FI cleaner) and ended all rough running, stalling, etc. problems.

 

[Porkchunker]

I have two of them on my 2510. The symptoms you describe are not normal. Sounds like something with fuel injection, or a bad sensor is fooling the computer software into making bad decisions.

 

[johnnycomelately]

Thanks guys, I am going to try the carb cleaner and if that doesn't work she'll probably go to the shop. Someone on another board also mentioned carb cleaner so I have my fingers crossed.

johnny

 

[DaleH]

Someone on another board also mentioned carb cleaner so I have my fingers crossed.

I'd try that for sure, and would use Deep Creep or Seafom from NAPA, but if you just spray it into the carb throats you're still missing part of the inlet manifold and carb bodies. It sounds to me like the intermediate jet could be clogged or set wrong, as sometimes doing the low speed idle and/or sync&link carb adjustments, eases the motor's runup from idle speed to throttle. But only do so using the Yamaha OEM factory service manual ... as I have zero confidence in a Clymer or Seloc manual in describing it correctly.

If I were you, I'd use Dunk's 'pony tank' method described here, as it would pull decarb/cleaner solvent throughout your entire fuel delivery system:

http://outdoorsbest.zeroforum.com/zerot ... 589&page=1

Also check the gap of your plugs yourself, an improperly gapped plug can cause lots of starting and weird RPM issues. This is a faster check, while the decarb method described above won't hurt your motor (actually helps) it, regardless of what else is going on with it.

 

[johnnycomelately]

Thanks for the advice and for the link. I'm going to try the pressurized version first and see how it goes. I'll repost in a couple of weeks once I get the carbs cleaned out and get her on the water with results.


johnny

 

[Porkchunker]

I have two of them on my 2510. The symptoms you describe are not normal. Sounds like something with fuel injection, or a bad sensor is fooling the computer software into making bad decisions.

Oops...I didn't read well enough to realize you were talking about 2-strokes. As stated above, junk in the fuel system is the likely culprit.