50TLR performance and timing issue

[jfleblond]

I have purchased a 50TLR 2006.
The engine has very poor performance at wot (about 10hp speed)). It also has a rough idling with sounds like backfires (I'm not a mechanic by the way)
I've been through 2 different repair shops. The first shop checked everything it could but didn't find the problem. The second one is a yamaha certified dealership with certified technicians. There diagnosis: a crooked crankshaft of 30mil where the flywheel sets in. It's almost not perceivable with the naked eye. They say that's enough to cause bad timing on the engine.
Both shops checked compression, spark plugs, coil, carburator, etc. Everything checks ok.
I have filmed a test that I made of the engine at wot :
https://youtu.be/73fDWV-tBfk
It runs rough and won't rev up at wot.
Can it be a malfunction that enables the rev limiter to kick in?
Do you agree with the diagnosis of a crooked crankshalf?
Thanks in advance
Regards.
JF Leblond

[pstephens46]

I would think a crooked crank would destroy the engine pretty quickly. But crooked may mean different things to different people.

Crapped up carb would be the first place many would look

[boscoe99]

Find a new mokanic.

Backfires are typical of a fuel/air mixture that is too lean. Not enough gasoline for the amount of air.

"They say that's enough to cause bad timing on the engine."

They make a device called a timing light. It is super easy to see if the timing is correct. 7* after top dead center, plus or minus one degree, is the correct fully retarded timing. Fully advanced 25* before top dead center. Plus 3 degrees or minus 1 degree. I am not seeing a flywheel causing the timing to be so far off that the motor runs poorly. Not without some other bad stuff going on at the same time anyway.

Mist some gasoline into the air intake system when trying to come up on power and see what happens. Fuel system issues are the number one problems on Yamaha's and maybe any other brand motor.

Oh, is the PrimeStart lever in the correct position?

[99yam40]

and check the fuel pump.

[rodbolt17]

can flywheel keys shear?
can a built up crank twist??
yeuuuup.
can it be quickly and easily checked with a simple screwdriver and a human eyeball and a tool betwxit the ears ????
yeuuuup.
once the mechanilal parts are verified.
the spark producing and spark con*****ing components have been tested, PROPERLY.
then fix the fuel system.
remember it is
SUCK
SQUEEZE.
BANG.
BLOW.
yep it is that simple.