Yamaha 115 v4 - tuning/diagnostic question

[Craig W]

Hi all! I'm not overly active with posts here, tend to read & reference more than anything else and REALLY appreciate everyone that contributes to this amazing resource.

I've run into some "challenges" recently with my 1985 Yammy 115 v4... it's been good for the last number of years, this year everything came to a halt. Had fuel challenges to start the year, 1. lots of smoke - choke solenoid stuck - (iboats search to the rescue) 2. great idling/no power - rebuilt fuel pump & carbs (that seemed to fix things) 3. then came tuning issues thought things were going well, however 4 carbs 4 times the headache... don't know if it was tuning or just the problems over the last year with fuel starving etc, but I burned out the #4 piston!

SO.. I'm in the process of rebuilding all 4 cylinders (guess they are due after 22 years) and I was wondering if anyone has used Exhaust Gas Temperatures (EGTs) to tune and maintain proper operations with multi carb/cylinder engines. I've used this with performance car tuning and just curious if anyone may have data on what Temps should be safe for a 2 stroke 115 HP outboard.

Any help or thoughts are greatly appreciated. TIA

 

[grid]

Re: Yamaha 115 v4 - tuning/diagnostic question

Pistons tend to run a hundred or so degrees short of aluminum melting, so making certain main jets are clear is paramount, since gasoline is the coolant. As far as I know, 2-strokes don't use EGT testing. The piston gets to be the guinea pig! Probably as 4-strokes approach the EPA barrier where converters will be required we'll start to see that sort of "report" going to the computer.

 

[Ray Neudecker]

Re: Yamaha 115 v4 - tuning/diagnostic question

Actually EGT's are available and used by many high performance and race people. 1200 degrees is very close to the meltdown.
Reading the plugs and using an inspection light to read the pistons is also a method used by most racers at almost every race.
Piston melting is not the way I would reccomend as a diagnostic tool.