jeffersondodson561
Ensign
- Joined
- Oct 28, 2010
- Messages
- 923
Re: 1990 yamaha pro 50 stalls
When you rebuilt carbs did you use new kits or reuse all of the needles and gaskets. Did you examine the needles and seats, look for a depression on the needle? Because it sounds like you are unable to transfer fuel to the top of the cylinder. This could be from a damaged piston skirt. Their really is no way to check primary compression but I have noticed that if you get some powertune ( OMC engine tuner) and squirt liberally into the #3 carb and see if you can get the cylinder to fire (this is some cases will create a seal if the piston skirt is damaged but it depends how badly it is damaged) another "test" is if you get a piece of paper and hold it in front of the carb. Watch how the piece of paper moves back and forth and note the amount of fuel on the piece of paper. If their is more fuel on the piece of paper on the number 3 than the others it may indicate that the piston is not able to transfer to the intake port as the piston moves toward BDC. This is really rare though, I have only seen this about 5 times in my entire career. Like I said these are tests that I have sort of had to invent because the only way to determine that the piston is scored is to tear it down. One more test is to remove all the coils except for #3 and squirt some fuel into the spark plug hole and quickly put the plug back in and start the engine and see if it pops off, but you know you have good compression. Without being there and doing these things myself, I am at a loss. Leaking labrynth seal? Flexed reeds? I dunno?
When you rebuilt carbs did you use new kits or reuse all of the needles and gaskets. Did you examine the needles and seats, look for a depression on the needle? Because it sounds like you are unable to transfer fuel to the top of the cylinder. This could be from a damaged piston skirt. Their really is no way to check primary compression but I have noticed that if you get some powertune ( OMC engine tuner) and squirt liberally into the #3 carb and see if you can get the cylinder to fire (this is some cases will create a seal if the piston skirt is damaged but it depends how badly it is damaged) another "test" is if you get a piece of paper and hold it in front of the carb. Watch how the piece of paper moves back and forth and note the amount of fuel on the piece of paper. If their is more fuel on the piece of paper on the number 3 than the others it may indicate that the piston is not able to transfer to the intake port as the piston moves toward BDC. This is really rare though, I have only seen this about 5 times in my entire career. Like I said these are tests that I have sort of had to invent because the only way to determine that the piston is scored is to tear it down. One more test is to remove all the coils except for #3 and squirt some fuel into the spark plug hole and quickly put the plug back in and start the engine and see if it pops off, but you know you have good compression. Without being there and doing these things myself, I am at a loss. Leaking labrynth seal? Flexed reeds? I dunno?
