150 yamaha 2 stroke bogging

[tommmmmg]

I have a problem with bogging above~3200rpm. Cold or hot and only under load Starts and runs well below that. Let me post a quick time line as I have spent a lot of time and $ on this including 3 trips to certified Yamaha mechanics
1 boat purchased at auction runs ok but bogs at ~3krpm
2 mechanic tune up same thing
3 carbs rebuilt same thing
I now put an external tank with new fuel and lines and primer bulb to the engine to eliminate bad gas and/or lines

4 mechanic says 2 carbs ng and not repairable wants $1500 to repair
5 bought "rebuilt" carbs I installed with the exact same results
6 brought to another yamaha mechanic checked timing, carb sync,linkage,oil pumps, and installed installed new fuel pumps
EXACT same results
One hint if while under load I by hand open the butterflys (fuel) while closing the choke se'll take off and go 5000rpm??
called another mechanic same line "let me take a look" Any ideas?? Thanks in advance Tom

 

[lmuss53]

Tried raising the floats a little? If the float valve closes too soon it will bog the engine until it opens and lets some fuel flow.

Will it run and keep running with the choke trick?

 

[tommmmmg]

Yes it will keep running with the choke ~ 1/2 closed. Well at least a minute. I didn't feel comfortable holding any longer that that. It could very well be the carbs but I'm doubtful because 3 times the carbs have been checked and the symptoms of bogging have not changed one bit. Correct me if I'm wrong but by choking I am increasing fuel to the engine. So i the engine is starving for fuel? Maybe fuel lines between the fuel pumps and the carbs??? All other lines have been eliminated

 

[lmuss53]

It is fuel restriction of some sort. If it were mine I would replace any line that hadn't been changed yet and if that didn't help I'd raise the floats a bit. If you have to pull carbs to change those lines I would raise the floats up little while I had the carbs off.

I know its a much smaller engine but we went round and round with my brother's 30 Johnny and this problem. The float looked like it was set right according to the kit instructions, but the motor would bog down. I flipped it over and bent the float down a couple degrees so it will open a little sooner and it runs like a scalded dog.

 

[tommmmmg]

Thanks I'll replace the remaining lines and check out the floats. Appreciated the suggestions

 

[lmuss53]

Let us know how you make out, good luck.