Yamaha 150 2 stroke - starting/idling rough

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phazzard

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Hi All-
Been out a few times this spring and have noticed an issue starting up. Engine cranks (choked) for 4-5 seconds three or 4 times before "catching"/sparking and starting up. At idle and slow harbor speed, it seems I'm not firing on all cylinders. As soon as I get to 2700-3000 rpms, life is good and I run very smooth. At first, I just put it down to being a little early in the season, but am getting a little concerned. New plugs this spring with normal "commisioning". I had some E-10 related fuel issues last year, but they were resolved by mid-summer with new install of a Racor filter and dumping a bad tank of fuel. Racor looks clean now... I've run her a couple of times at WOT in hopes of clearing carbs and she sounds good at anything over 3000 rpms.

Any input on what or how serious my problems are? Dirty carbs? Other? Thanks for any input.

Pete H
 
phazzard said:
Hi All-
Been out a few times this spring and have noticed an issue starting up. Engine cranks (choked) for 4-5 seconds three or 4 times before "catching"/sparking and starting up. At idle and slow harbor speed, it seems I'm not firing on all cylinders. As soon as I get to 2700-3000 rpms, life is good and I run very smooth. At first, I just put it down to being a little early in the season, but am getting a little concerned. New plugs this spring with normal "commisioning". I had some E-10 related fuel issues last year, but they were resolved by mid-summer with new install of a Racor filter and dumping a bad tank of fuel. Racor looks clean now... I've run her a couple of times at WOT in hopes of clearing carbs and she sounds good at anything over 3000 rpms.

Any input on what or how serious my problems are? Dirty carbs? Other? Thanks for any input.

Pete H
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Running at WOT won't clean the carbs.
On epoosibility is dirty carbs, the idle jets may be gummed up. You will need to dissasemble them and clean/inspect the jets, needle valve and seat , float and float adjustment.
 
Yamaha 150 Probs

SeaFoam is good, but you could also use additives everytime you fill up like Pri-G or Marine Stabill. Both products clean the fuel system, and then running Yamaha Ring Free all the time should keep the engine happy. I've been using Pri-g along with Ring Free for 3 years now, and as long as the fuel system is primed by squeezing the ball, she starts up in just a second or two. Some guys may say it's overkill, but no problems so far and it runs great.
 
Had an issue with my two stroke hiccuping at idle. It was the O2 sensor which was replaced and all now runs fine. The mechanic also adjusted the timing. Have a certified Yamaha mechanic check the O2 Sensor.
 
Striped Bass. I also have Yamaha 150hp 2 stroke. Where is the O2 sensor located on the motor?
 
My '97 model carb motors have a drain plug in the side of each float bowl.
If yours are similar, you could try removing the drain screw and flushing out with carb/choke cleaner like Gumout. If you have to remove the carbbuy a rebuild kit before you start. Be sure to replace the gasket that the carb sets on when remounting to the block. Also -- Be careful to not over-tighten the nuts that hold the carb to the engine. It's easy to snap off a stud.
Chances are the carbs need to be removed clean and checked for proper float level. I discovered that my floats were off by as much as 3 mm and I was the first person to touch them from the factory installation.
BTW -- I went thru the same problems with E10 last year and ended up cleaning out the carbs on both engines 3 times.
 
If you have carbs there isn't an O2 sensor. It does sound like it's time for a carb rebuild.
 
The O2 sensor on a Fuel Injected OX66 225 is on the starboard side of the engine near the rear. There are electrical wires leading from it to the rear of the engine and up along side the starboard side. You can see what the O2 looks like by Googling Yamaha Outboards and selecting the parts and service tab.

Grog is correct in that carbed Yamaha outboards do not have an O2 sensor.
 
Maybe the carbon inside your engine is already thick. You might need to de-carbonate it.
 
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