1993 yammy 2 stroke 6 HP Need Opinions

[w2much]

This engine will not run on two cylinders. Has great spark. Both cylinders fire blue spark which jumps 7/16 easily. Compression on dead cylinder is 85lbs . This seems to be plenty although I would appreciate your opinions on this. Cylinder is getting plenty of fuel. I can run the engine with the top cylinder plug in place and the bottom cylinder plug removed. Plenty of fuel comes out the Bottom cylinder when running this way. Had carb problems . I rebuilt the carb but I am also curious if this running issue can be attributed to a bad carb.Bottom plug is wet with fuel when removed.

 

[99yam40]

what does the other cylinder have for compression?


good compression, good spark at the proper time, and the proper fuel to air ratio is what a motor needs to burn the fuel in the cylinders

 

[w2much]

Thank You, My real concern here is should the cylinder fire at 85 pounds compression. I know its a bit low but seems as though it should still fire.

 

[robert graham]

Maybe bad fuel pump diaphragm causing raw fuel being sucked into that cylinder?....

 

[w2much]

Pump is integrated to the carb not the manifold. Can this still cause this issue? Will a bad diaphram do that on this motor. I have worked on Evinrudes and run into that being the issue where raw fuel is sucked in before it gets to the carb . It seems to be getting lots of fuel to the lower cylinder as the plug is always wet. BTW compression is even on both cylinders and is probably a bit higher than stated above as I used a harbor freight compression tester. I will take the fuel pump apart and replace the diaphrams if the answer is yes.