1994 yamaha 250 wot problem

[1stpriority]

I have twin 1994 yamaha 250 txrs outboards on my boat. The right motor runs strong up to 5700 rpm and the left is having problems at wot it will go to 5400 rpm. They used to both hit 5700. When I gun just one motor at a time the right runs strong to 4300 by itself and the left feels sluggish and hits 3700. I ran all new fuel lines , new fuel fiters and rebuilt the carbs. It has good response off idle but just doesnt have the power. like the right one. good compression 115 to 120 all cylinders. The next step I am guessing is the timing not advancing for some reason. I hooked the diagnostic light up to it and no codes showed, I am shaking my head what to do. Any help would be appreciated

[boats.net]

Check timing and throttle linkage adjustment and synchronization.

[richd]

I had a similar problem, check the squeeze ball, mine was faulty but the real problem was junk in the fuel tanks anti syphon valve restricting fuel at WOT.

[1stpriority]

I think I am going to run a separate small gas can to motor just to rule out anything from the tank to engine because I replaced fuel pumps, tstats, fuel line, filters, rebuilt carbs, I cant think of any other thing I can do with fuel. thats why I was thinking timing, oh I re-synched the carbs twice and replaced the tps. Question for timing I belive it should be 6 btc at idle and up to 18 btc at wot. I guess I am going to have to hang off the back with a timing light while the boat is wot

[1stpriority]

I ran the boat yesterday wide open the timing advanced to what it should be 18btc and I also squirted a mix of gas and oil right into the carbs with engine wide open to rule out a lean problem and no result, did nothing. Any help would be appreciated.

[99yam40]

In my opinion ,if there is good compression, timing is doing its thing correctly, and no cylinder is running lean. The only thing I can think of is, something has to be causing a cylinder not to fire,either you are running rich on some cylinder or you are loosing spark. Jets in wrong carb, weak spark, bad plug, bad plug wire or coil. There are ways and equipment for testing the ignition systems on these motors

I found out someone (previous owner)drilled out the main jets in my C40 after a year of searching for a WOT cylinder dropping. Good luck and keep us informed of what you find

[1stpriority]

I was think loosing spark also. I put new plugs in. My question is how do I test the spark at problem range. It runs fine at idle and up to about 3000rpm, then I feel power drop. The manual doesn't show how to test at rpm range or I am reading it wrong.

[99yam40]

Not completely sure on your motor, but normally a peak reading volt meter or a meter along with a DVA adapter and a test harness is used to measure the inputs and out put of the CDI. This should show a out of spec voltage. The diagnostic light should show something failed, but may not something out of spec.
A timing light will also show a non-sparking wire by moving the light to different plug wires, and if it is one that reads RPM also it will show the lose by changing the rpm dropping farther that the other cylinders.
A high voltage tester can also help see the output of the coils at the plug