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No Fuel In 3rd Cylinder

"I need your help again. My tr

"I need your help again. My trustie lil 50 HP 1989 Yamaha has give me troubles again.
I took it to the shop to do the sync and link. The mechanic called me and said the bottom cylinder was not receiving and burning fuel. Got 125 psi in all cylinders, good spark, clean carbs, and the reeds were checked and found to be ok. I have had this motor rebuilt with new gaskets pistons and rings. I have 3 mechanics stumped on this one. This last mechanic mentioned a seal on the crankshaft in between the pistons could be bad. He's talking as if it is a ring on the shaft that seals the cylinder. Problem is when I had the block open I don't remember seeing anything like that. I saw the half moon I think they call it the labyrinth seal. Which leads me to another question. That labyrinth seal, my manual shows it in the block, the half moon I remember seeing was on the shaft, is that the same and is it supposed to be there on the shaft.
Any input would be great.
Thanks in advance."
 
"Peter, you mention this was r

"Peter, you mention this was rebuilt - any chance that the bottom piston was installed the wrong way around?? with the exhaust/intake sides reversed????"
 
"Not unless the piston was mis

"Not unless the piston was mismarked. I made sure when I put them in, they all had the arrow pointing up."
 
"Ok, was kinda reaching there.

"Ok, was kinda reaching there. With the compression good in all cylinders it doesn't really sound like you have a "leak"..."
 
"It can only be a plugged carb

"It can only be a plugged carburetor jet or a lack of crancase compression ( blown seal,poor assembly with respect to the joint of the block, labarynth problems or worse a hole in the crankcase ).Cylinder and crankcase compression are a totally unrelated thing.YES you can have top notch cylinder compression and zero crankcase compression."
 
"When I checked the compressio

"When I checked the compression I had 125 psi in each cylinder. The mechanic that has it now says the bottom has about 10 psi less now. But that could be contributed to the last mechanic pulled the intake to check the reeds.
Looks like I am going to pull it apart again. Let me ask this, where is the labyrinth seal supposed to be? Resting in the block when I place the crank back, or attached to the crank already? Also, how should the seal be? With the head side down, the crank rests in the block. Does the seal slide completly into the slots on the block, or should they be facing points down and just the edges in the bottom part of the block.
Is that labyrinth seal the only seal between the 2nd and 3rd pistion?"
 
"I am going nuts here. I got t

"I am going nuts here. I got the boat back from the shop. Before I crack this thing open again, is there an easier way to see what the problem is. I pulled the plugs and they are a little wet, even the 3rd cylinder looked wet a couple times. I tried swaping carbs around and there was no difference in the wetness of the plugs or the way the motor sounded.
When I pulled the carbs, you can in down into the reeds, and they were all wet. When you accelerate the motor you can see fuel droplets coming into the carbs.
Any Ideas?
Any good mechanics out there near Georgia? I am at my wits end."
 
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