2001 Yamaha 50TLR Stalling

[Tbone18]

My 2001 Yamaha 50tlr is stalling around 2500 rpm. Carbs rebuilt, new CDI, link and sync completed. If I quickly throttle past the "stall" position it never misses a beat. If I ease throttle up it stalls. Also, if I trim motor up a little it doesn't stall. Floats are set correctly. New fuel pump. Starter primer working. Have tried disconnecting all of the safety features such as low oil, overheat sensor. Tried everything. Sprayed carb cleaner looking for air leaks. Nothing. All seems good. Anyone have any idea what else to check? Fuel good. Water separator clean. Compression good. Went through every possible issue I can think of. Any ideas from here? I'm at a loss. Don't know what else to check. The trimming it up a little and it runs fine really throws me off. Seems like fuel issue but I've completely checked every single thing related to fuel. Help! Help!

 

[99yam40]

not sure what you mean by this
The trimming it up a little and it runs fine really throws me off.

Anyway if the timing is off it could cause problems,
but it sounds like your pilot jet/passage could have a problem still.
as you transition between idle and high RPMs there are off idle passages that need to add the extra fuel.
Maybe your pilot screw settings just need a little opening to help with the transition if the other things I mentioned do not help

 

[Tbone18]

I mean when I trim the motor up a little it doesn't stall or miss a beat. Runs like a top. Trim it all the way down or almost all the way down and it starts stalling/bogging down. I have visually watched the high speed jets and they don't have any fuel come from them when it does this. Floats are set and timing is set correctly. Seems to be the transition from low speed to high speed is where the issue is. I've cleaned carbs in ultrasonic and blew them out with air. Checked every orifice. All seems good. Do you think a larger jet size would help solve this problem? Maybe the high speed jets are orificed too small? I dunno. Grasping at straws here.

 

[99yam40]

If you have good compression and good spark along with the proper timing then you are left with not the proper fuel to air ratio for the spark to ignite the mix in the cylinders . too much or too little will cause problems

I do not see how tilting the motor up some would affect anything except moving some of the wiring around maybe and causing some wiring to short or loose connection maybe


Is this happening cold and hot?
is the red lever in the normal(automatic) position

Make sure the timing is at proper idle spec and that it advances as it should when opening the throttle while this problem shows up

Also make sure the prime start enrichment system is working properly

Did you follow the link and sync procedure in service manual after

 

[Tbone18]

Doesn't matter hot or cold. Lever is in the run position. Prime start working properly. Link and sync followed. Timing is set correctly and advances properly. I've literally checked everything I can possibly think of at least 3-4 times or more. Doesn't make any sense at all to me why trimming motor up would change anything either. Like I said. Just looking for some sort of possibility I've missed. Jet size make any difference?? I'm at a loss here.

 

[99yam40]

A previous owner of the C40 I am currently running drilled out the main jets on all 3 carbs.
It took me close to a year to finally figuring out what was causing my high speed miss.
put the factory engineered ones back in and she runs fine now.

These motors are designed to run properly with the parts that come with them new so I would not be changing things up.
You did see that not all the main jets are the same size , and made sure they went back into the correct carb when putting back together

what is your idle timing set at and what does the timing go to when advancing the throttle?
does the timing lag behind when the problem shows up?

 

[Tbone18]

Timing is set at 7* ATDC at idle and advances to I think 27* BTDC at full throttle. I can't remember but it is set to where the spec calls for. You hit on something I totally forgot to check! The different size jets in the different carbs!! I bet anything that is going to fix my issue. Runs way to good to be much of anything. I'm pulling the carbs and checking the jet sizes on them. I'll let you know how it works out. Thanks a ton!

 

[Tbone18]

Ok. So what jets go where? Can't find it in the manual. I know for a fact I put them in the same carbs they were removed from but I also know someone worked on these carbs twice before I got the motor. They may have mixed them up. I don't know. I am going to check the jet sizes and see if they are different sizes. Doesn't show to be in the manual. Went through the link and sync again. Just to make sure. All was good so it's down to the carbs and jets and when the transition to high speed pick up. Definitely not making the transition when a smooth throttle advance is made. Do it quick and it works fine. Just when you slowly ease throttle up is when the stall occurs. And it's definitely the high speed transition. I can watch them and see the fuel NOT come out of the high speed when slowly accelerating. Do it quick or trim the engine up and it does fine.