Am I missing something?
09-03-2002, 07:46 AM
#1
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Engine "Break-in"
Sounds like the carb is set up wrong.... Possibly running too lean at top end and too rich at low end.
Too lean at top makes the cylinder expand excessively, reducing compression by allowing the gasses to pass between the piston and cylinder. This makes starting very difficult. The high temperatures are very bad for the engine too.
The dieing out with sudden throtle reduction (and usually also dies when you suddenly accellerate after idling for a while) normally shows that the engine is "quenching" the plug. The momentum of the propellor can increase the vacuum in the intake on sudden throttle reduction, pulling more fuel than needed, and the result is fuel droplets going into the cylinder, rather than a fuel-air vapor mix. A droplet hits the glow element durring intake, and its "lights out."
Its probable that an experienced modeler could readjust the engine in less than 5 min.... This is one place where having someone else who has done it before helps a LOT.
Too lean at top makes the cylinder expand excessively, reducing compression by allowing the gasses to pass between the piston and cylinder. This makes starting very difficult. The high temperatures are very bad for the engine too.
The dieing out with sudden throtle reduction (and usually also dies when you suddenly accellerate after idling for a while) normally shows that the engine is "quenching" the plug. The momentum of the propellor can increase the vacuum in the intake on sudden throttle reduction, pulling more fuel than needed, and the result is fuel droplets going into the cylinder, rather than a fuel-air vapor mix. A droplet hits the glow element durring intake, and its "lights out."
Its probable that an experienced modeler could readjust the engine in less than 5 min.... This is one place where having someone else who has done it before helps a LOT.
09-05-2002, 08:06 PM
#2
Am I missing something?
Dont want to argue with anyone, but I would say that if you are following the manual, then dont expect the engine to run right while its set super rich at full throttle setting. If thats where its set, then lean it to where its a little rich, and it will run right if the tank is plumbed correctly. Seems like after rebulding thousands of motocross bikes,(same thing as a two stroke plane engine, with a tranny), that when a moter runs lean, the piston swells and freezes at four points in the cylinder. This is why so many folks were frying their O.Ss a couple years ago, and then blamed O.S for bad plating. I fixed a bunch of them around here. The cylinder will never swell more than the piston. Dont want to argue with anyone, but thats the way it is.
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09-05-2002, 09:37 PM
#3
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Engine "Break-in"
Tell my somewhat worn out engines that the piston's supposed to expand more than the cylinder, and stay that way for a hot restart.... I've got a few that will run OK (for trainers and such) but won't hot re-start at all due to lost compression from the cylinder expanding more than the piston. (feels like 0 compression when hot. Already marginal when cold I'll admit.)
And... ABC engines by design have the upper cylinder expand faster than the piston. freeing up the piston as they get warmer. That's why the new engine is VERY tight at TDC, and loosens up, becomming quite easy to turn immediately after its been run.
Motorcycles don't use ABC construction. Totally different metalurgy involved.
And... ABC engines by design have the upper cylinder expand faster than the piston. freeing up the piston as they get warmer. That's why the new engine is VERY tight at TDC, and loosens up, becomming quite easy to turn immediately after its been run.
Motorcycles don't use ABC construction. Totally different metalurgy involved.
09-06-2002, 12:57 AM
#4
this will be my last comment
yes abc engines are tight.run one lean when its cold, and watch it seize. Same when its hot. Do you know why a motor sags in the air or on the ground when too lean? the piston has grown larger than the cylinder, and is fixing to seize. also, call yamaha, and tell them that the aluminum piston we run, dosent go with the crhome plated brass cylinder they ported for me. We also run k and b sportster type cylinders,(no sleeve) that are all cast aluminum, with a solid aluminum piston. Its not brain surgery, its the same thing. I am through with this, and its not any help to the man above that cant figure out his problem. your engines have no compression cause theyre worn out. good luck, and dont fry your engines.
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