Flywheel removal

[tweekster]

The enrichment valve was to blame on that #1 cylinder, I chased a miss forever, low to middle throttle response was bad, I rebuilt the carbs 3 times thinking it was something in there, but all along it was that valve. Finally found that that was the problem, fixed it, ran great finally, then seized up. The slop on the wrist pin did not seem outa line, and the same for the crank, for a 92 #3 cylinder actually seems the worst for slop, and #2-3 cylinders are fine. The top bearing is toast, but may have been part of the problem also. As for price, well hoping for the best but I have about a 1300.00 figure in my head to get this done. I don't really know, never did a 2 stroke before, but I do know I would rather fix it and know what I have, then buy a used motor! And a new one is way more than that! Still open for any opinions, advice, so I can get this done!
Thanks Ron

[99yam40]

enrichment system would have affected all 3 cylinders not just #1.
That valve should not affect anything once motor has warmed up as it closes off the extra fuel. What did you find wrong with it?

The top bearing going out probably took out the seal at the top and let in air leaning it out.
Question is what took out the top bearing.
Rodbolt has said that bad main bearings are usually do to corrosion/rust which comes from moisture

[tweekster]

On my motor, the enrichment system feeds just the top cylinder, and the diaphram was leaking dumping fuel in all the time, also one of the carb rebuilds I did, the new floats that came in the kit, filled with fuel and leaned that cylinder out also, I don't think this happened at once, but rather did it over time, then when I finally fixed/found the enrichment valve and made it run correct it finally had enough. I hope I'm right on the enrichment system, please tell me if I'm wrong, because I would have to fix the problem before the rebuild. I don't believe it was closing after warm up. I found the bad float while the silencer was off watching the carbs work on the water, and you could visible see that carb putting more fuel into the cylinder.

[99yam40]

The enrichment system runs to the top of the intake, but has passages that lead to the other intakes from there. With it apart you should be able to trace that out with no problem

If a float allows too much fuel into the carb it will not run lean it will be too rich

[tweekster]

I will look at those passages close today for the fuel enrichment, just looked like it would flood the 1 #cylinder, and on the float sticking, with oil injection, how would it run rich with more fuel? The injection system puts a metered amount in the cylinder from the position of the throttle, thats what I thought, from the rod connected to the bottom of # 3 carb, am I wrong on that? If I am I'm clueless on why this destroyed that piston.

[rodbolt17]

when we say rich or lean we are referring to the A/F mix not the oil ratio.
usually lean oil ratios take out bearings and turns crank journals blue.

[Solarman]

I'd agree with both. The injection system lubes crank/bearings area first as it enters each cylinders chamber, if carb dumping extra fuel mixes with oil, leaner than the 100 to 1 ratio, might be 200 to 1 at piston... gets the short end, while crank/bearing did get some damage, it doesn't look blue.

Ok, my thoughts. Just trying to imagine the blending of oil as it proceeds through the chamber.

Good luck tweekster.

[tweekster]

My top bearing and top piston are trash, scored up the piston but the cylinder really isn't that bad, most of it is debris from the aluminum piston stuck on the walls. Had a slight leak at the seal under flywheel, but didn't look real bad. Rod and crank bearings where still decent, for a 1992, showed wear but nothing outa line, so if it was getting to much air, what could be the cause? I have pics if any would help.

[99yam40]

If top crankcase is sucking air from anywhere but through the carb then the fuel to air ratio is off and you end up with smoked piston.

A plugged or partially plugged main jet will do the same thing. Lean fuel to air ratio

[tweekster]

Did a lot of looking, I can almost rule of an air leak, unless it was the top seal under the flywheel. That top bearing is seized up and just can't tell if it was part of the end result, or cause of the problem. Really the only thing that makes sense is age and small issues of to much fuel over a long period of time and when finally made right and running well the engine failed. If anyone has things I can look for it would be appreciated! While my crank and block are getting done I'm going to go thru the oil injection, and carbs again for piece of mind. Thanks for all the help!

[rodbolt17]

your describing a lack of lubrication.
the oiling system cant make up for excessive gasoline from a blown enrichment pump or fuel pump diaphragm.

most likely debris took out the piston.

[tweekster]

Thanks for all the help, much appreciated! Crank and bock off to Carolina Machine today, thank you Rodbolt! Now to find some good Pistons after I find out what size, gasket sets, new reed valves. Any suggestions

[rodbolt17]

cant go wrong by simply ordering the correct oversize from Yamaha.
you can get them from this site or Carolina machine can get them.

call them back and talk to Ken.

[99yam40]

Question for Rodbolt or others that have ordered pistons before.

When ordering pistons from Yamaha or else where.
what all comes with the piston and what needs to be ordered separately?
wrist pins, keepers, wrist pin needle bearings, rings?

[tweekster]

From what I am finding it is such a mixed bag that company's offer on rebuild kits, right now to order Pistons and gasket sets it is almost cheaper for me to order a hole set with everything including the bearings ( which the machine shop is pressing on) than to buy it all separate.