View Full Version : Problem with 1998 Yamaha 115 2 stroke

08-12-2009, 12:26 PM
"I am completely baffled as to the problem with my motor (1998 115 2 stroke).
I am the 2nd owner of the boat/motor, in my 3rd year of ownership. When I had the boat surveyed prior to purchase, the motor was compression tested, all cylinders came back as follows : 145,145,150,145. The surveyor also mentioned that the motor was in excellent shape. The previous owner definitely took care of her. I have been taking good care of her as well, and I have been having her professionally winterized every fall.
I first used the boat this season in early April, started right up on a mix of the winterized fuel and fresh. I topped the tank (60 gal) with fresh fuel 2xís up until June when I started to have problems.
My problem is as follows:
Motor would fire right up (normal cold start procedure), idle rough(500 rpm), cough, sputter, stall. I know that the motor should idle higher (~800 rpm). I inspected, and changed the in-line 10 micron fuel/water filter as there was a small amount of water/crud in the filter. I also checked my plugs for gap (1.0), they were gapped correctly and looked normal. I also hooked the motor up to pony tank (1 gallon fresh fuel). I had the same problem, rough idle stall. With the engine cowl off, and when I pumped the primer bulb (engine off), I saw some raw fuel drip around the fuel pump.
My boat is on a trailer, so off to the mechanicís shop I go. I described all the symptoms, and I mentioned the fuel near the fuel pump. Mechanic (Yamaha 5-star cert) tells me that it sounds like the carbs. I never had the carbs cleaned, so I said go for it. The shop had my boat for almost a month (July). When the boat was ready, I was told that my carbs were very dirty, and that they did the ultrasound cleaning, new carb kits, new filters engine mount and in-line, they did compression check on cylinders, checked CDIís, stators, overall check, everything was ok.
I took the boat back to the marina, started the motor on ear-muffs, as I was going to take the boat out, ran ok, launched, ran for a while, returned to the ramp, and boat started to idle rough again and continued to cough, sputter, stall multiple times as I hooked back onto the trailer.
Ran the motor on ear-muffs again, terrible. Ran it on a pony tank(fresh fuel), terrible. I then took the boat back to the mechanic.
He advised me that the carbs got dirty again, and he had to reclean. No charge, he assured me that it will work fine. Took the boat back to the marina, ran on ear-muffs, ran ok, set-up to launch, shifted from neutral to reverse, rpms dropped stall. Dead in the water, restarted, idled rough, cough, sputter, stall. Was able to drift onto the bulkhead, tied off, and was able to drag the boat back onto the trailer. Took the boat back again to the mechanic (3rd time).
It is now beginning of August. I picked the boat up last Friday Aug 7th, mechanic showed me a fuel sample he took from my fuel/water filter. Looked like a Guiness stout. He also mentioned that they kept my boat in the water for a few days, ran it everyday, and actually used it for a shop boat to make deliveries in. He told me that it never stalled once, and ran fine.
The mechanic advised me to drain the fuel tank, and start over with fresh fuel, and to put a treatment of E-zorb in the tank.
I did all that he advised to do. I drained the roughly 20 gallons that remained in my tank, and I took fuel samples every few minutes. My fuel looked fine. It looked nothing like the fuel samples he showed me. Keep in mind that I was siphoning the tank through the fuel line that goes into the motor, so it was passing through the in-line 10 micron canister fuel filter. After I drained the tank, I inspected the canister fuel filter, there was very little water in the filter. I drained the canister re-installed, added 10 gallons of fresh fuel, and e-zorb.
I hooked the motor back onto ear-muffs, fired up, and guess what?. It idled strong, then proceeded to fall off, and stall.
I tried running it at fast idle, it ran ok, but when I shifted into neutral, it stumbled and stalled. No alarms are sounding, the water pump if pushing plenty of water through. The motor fires right up, I did notice that right before it stumbles, if I pull the manual choke out, and push right back in, it catches up, and idles around 800 rpms for about 10 seconds then stalls. My primer bulb remains stiff, and when I go to restart, it fires right up. I also installed a new low pressure fuel pump. When I removed the old one, the gasket behind the pump was pretty chewed up. I installed the new gasket and pump, checked for leaks(ok), and tried running the motor on ear-muffs using the main tank, and a pony tank. No difference, same results.
I am absolutely stumped. I have since brought it to another Yamaha mechanic, just awaiting his diagnoses.
I am so confused as to why my carbs keeps getting clogged, as my fuel looks clean, the filters are catching moisture. I am also a little annoyed about the fuel samples I was shown by the first mechanic shop. It looked nothing like my fuel. I have been using the fuel that I drained from my tank, 30 gallons in total in my truck and my wifesís car with no problems.
I know this was long-winded, but does anyone have any idea what the problem can be?, or has anyone had any similar issues?

Thanks for listening,