2006 Yamaha 90 2 stroke

[Jkingman28]

So.... my buddy and I recently rebuilt our 90 Yamaha. Put it all back together and it started up on the 3rd try. Ran for a few minutes. Then we shut it off.
next day I go back to it and try and start it up. Won’t start. So I take the carbs off put new needles and gaskets in them.
it now will start for about 5 seconds then shut off. Try and start it and it backfires bad. I’ve adjusted the pilot jet and everything.
I am stumped. Could it possibly be bad reed valves?

 

[99yam40]

make sure the compression, spark and timing are good,
if so then that leaves proper fuel to air ratio to chase down
needles and gaskets are not the only thing in carbs that can have problems.
jets and passages all thru them need to be clean

 

[Jkingman28]

make sure the compression, spark and timing are good,
if so then that leaves proper fuel to air ratio to chase down
needles and gaskets are not the only thing in carbs that can have problems.
jets and passages all thru them need to be clean

Compression is good and has spark. How do I adjust the timing though? I replaced the cdi box about 4 months before the rebuild

 

[Jkingman28]

Compression is good and has spark. How do I adjust the timing though? I replaced the cdi box about 4 months before the rebuild

I cleaned and re cleaned all passages on the carbs. I am just stumped why it fired up once and not since. I’ve spend hours trying to get everything dialed in

 

[99yam40]

CDI should control the timing as long as you follow the procedure for link and sync in service manual.
all 3 carbs need to be exactly the same closed on the carbs and setting the timing with the linkage is part of the link and sync

could be a lean sneeze instead of a back fire you were talking about, or is the loud pop coming from the exhaust prop area

 

[Jkingman28]

CDI should control the timing as long as you follow the procedure for link and sync in service manual.
all 3 carbs need to be exactly the same closed on the carbs and setting the timing with the linkage is part of the link and sync

could be a lean sneeze instead of a back fire you were talking about, or is the loud pop coming from the exhaust prop area

Loud pop is coming from the exhaust.

 

[99yam40]

that means unburned fuel is getting in the exhaust and then igniting.
need to make sure all plugs are sparking

 

[Jkingman28]

that means unburned fuel is getting in the exhaust and then igniting.
need to make sure all plugs are sparking

Would improper grounding cause this. I remember when we were putting it back together we couldn’t find a place where a ground wire setup went. It was a w shape with three eye clamps on it.

 

[Jkingman28]

Would improper grounding cause this. I remember when we were putting it back together we couldn’t find a place where a ground wire setup went. It was a w shape with three eye clamps on it.

 

[Jkingman28]

Anybody?

 

[Jkingman28]

Well I ended up taking it to a boat mechanic. And he found that the flywheel was loose and it ended up shearing the key. Runs fine now

 

[99yam40]

good to hear you found the problem and thanks for coming back to report what the problem was.

I would think hooking up a timing light would have shown it was not firing when it was suppose to

 

[robert graham]

flywheel was removed for rebuild....was the flywheel nut torqued to specification upon reassembly?......

 

[Jkingman28]

I thought I tightened it to spec but I may have overload it.
also the mechanic told me there is a bearing going bad on the crank. I assume that it is important to replace them?

 

[robert graham]

If there is in fact a crank bearing going bad then it will need to be replaced....but how does the mechanic know it’s going bad? ......just by a sound? ....these motors are known to make lots of sounds and noises...