Yamaha 115 power loss at high speeds

[GZimmerman]

I have no trouble starting and idling my '95 115 yamaha. As soon as I put a load on it the engine tries to die out and I have to pull back on the throttle to keep it from dying out completely. I have had this problem for about a year now. I had the carbs cleaned first and have been trouble shooting since then. I change the diaphram and fuel filters. I have run from a new tank with fresh fuel. It runs fine in neutral or if in gear with the muffs on it, however as soon as I run it in the water I can't get the RPMs over 2400. Is there any other direction I should be going in. I have brought it to the dealer three time and each time I get it back it runs normal the first trip. But the next trip out it is right back to running bad again. I don't get it. I am tired of giving money to a boat dealer the can't figure out my problem. Someone suggested the CDI unit but that is an expensive guess. Someone also suggested that the carb may need cleaning again but I have been attempting to run the engine regularly since it was cleaned the first time. I guess I an looking for suggestions which direction to go in. Any help would be greatly apprecitated.<br /><br />Jerry

 

[shooter243]

Re: Yamaha 115 power loss at high speeds

You might want to try running with a seperate hose and tank. Still sounds like a fuel restriction problem.

 

[douglloyd]

Re: Yamaha 115 power loss at high speeds

Next time you get the carbs rebuilt make sure that you have the dealer empty and clean out the fuel tank, Install a fuel water seperator and cross your fingers.

 

[GZimmerman]

Re: Yamaha 115 power loss at high speeds

Thanks for the reply. I will do these suggestions. Do you think the CDI Unit could cause this problem? Is it common for the CDI unit to go out on a Yamaha?

 

[ianyoung77]

Re: Yamaha 115 power loss at high speeds

Gzimmerman,<br /><br />I have been down this road myself. Whilst I am not quite at the end at least my motor is running heaps better.<br /><br />One suggestion I would make it to do the electricals first. They cause intermittent problems and make carby tuning a nightmare. When you are 100% sure you can move onto other areas.<br /><br />I would check coil resistances first (charge and pulser) then coil outputs for both. Then check the ignition coils. Check the scondary by removing the spark plug cover and putting one end of the meter on then end of the plug and the other on a ground. Move the lead around to check there are no poor connections. While you are connecting your meter to ground it is a good idea to check the ground connections are all together and solid.<br /><br />Next check your spark. I usually just use a bit of wire for this. Check resistances after reinstalling spark plugs<br /><br />Then move on to your timing. When checking your timing you are effectively checking your CDI. Your flywheel should have a mark for all 3 cylinders at TDC. Check the relative firing of all cylinders then connect to 1 and disconnect the linkage to the CDI. By moving the advance lever you can check the CDI is working ok. Take care to quickly check fully advanced timing since you do not want to overrev in neutral. You can repeat for all cylinders but my guess it you'll find they are ok.<br /><br />The tricky bit is testing this when the motor is both good and bad. Like yours, mine is always good with the timing light in hand!<br /><br />Good Luck, Ian

 

[GZimmerman]

Re: Yamaha 115 power loss at high speeds

Thanks for your help. I think my problem was in the Carbs after all. I didn't trust that the mechanic that rebuilt the carbs did a good job so I gave it a shot myself. Reading this forum gave me the confidence I needed to tackle the job myself and I am glad I did. After rebuilding the carbs over the weekend, I took the boat out today and she ran like the day I bought her. I was running at about 4900 RPMs and no hesitation at all. Plenty of power.<br /><br />Thanks

 

[GZimmerman]

Re: Yamaha 115 power loss at high speeds

Well back to the drawing board. I Took the boat out today and it ran great for about 20 minutes until I hit a huge wake from a tugboat. The buzzer sounded for a second as I pulled back on the throttle. Everything seemed ok at first. My light on the dash was green, the engine was running fine and no buzzers were sounding. I assumed that maybe the motor had come out the water and sucked a little air. So I got back on the the throttle but I could not get over 3700 RPMs. It ran smooth but I couldn't get over 3700 RPMs. I know there is some sort of safe mode but I would think that if everything else went back to normal that I should not have had the problem. Any clue on what I should do at this poine?