Spool/Down
09-06-2005, 11:31 AM
#1
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Spool/Down
Hoping someone has an answer for me!---I have a (actually have two,but same problem with both) YW48cc twin that I love, BUT it seems to take forever to spool/down when I pull back on the throttle!---Am I just spoiled by four/stroke glow throttle response (both up & down)??---I know that "Lean" low speed mixture settings will aggravate this & I have richened this to the point that transition is not good & the midrange is terrible, high speed seems to be "Spot On"---Has this got something to do with engine cylinder "Porting" & muffler type??---Are they shipping the wrong carb. on these engines??---Please somebody, whats going on?---Driving me Nuts!!
Thanks Guys---
Ed
Thanks Guys---
Ed
09-06-2005, 05:27 PM
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RE: Spool/Down
Air leaks into the crankcase on two strokes and excessive heat will also cause a high idle. A low restriction exhaust may also contribute to the problem.
09-07-2005, 09:54 AM
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RE: Spool/Down
High idle is not the question, but throttle response (spool-up/down) is.
Example: A two stroke bike does not have the engine braking action that a 4-stroke shows, nor does the trottle response match the 4-stroke engine.
The lack of braking is due to extremely low pumping losses in the two stroke once the throttle is closed at high speed.
During the process, extra fuel mist accumulates at the crankcase walls and case pockets. This extra fuel must be cleared out again when the throttle is applied, so there is a lag where the mixture strength is undefined, resulting in less than optimum power, and reduced spool-up speed.
Example: A two stroke bike does not have the engine braking action that a 4-stroke shows, nor does the trottle response match the 4-stroke engine.
The lack of braking is due to extremely low pumping losses in the two stroke once the throttle is closed at high speed.
During the process, extra fuel mist accumulates at the crankcase walls and case pockets. This extra fuel must be cleared out again when the throttle is applied, so there is a lag where the mixture strength is undefined, resulting in less than optimum power, and reduced spool-up speed.
09-07-2005, 07:51 PM
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RE: Spool/Down
Pe:
I know in theory that a two stroke won't have the engine braking of a 4-stroke, but in the real world of model planes the two stroke (if operating properly) will come down to low idle very quickly when you chop the throttle. They also spool up quickly if you use a light weight prop. Two stroke engines that don't decelerate quickly usually have an air leak (bad bearing seal typical).
In MotoGP, they've figured out a way to eliminate engine braking in a 4-stroke. The engine management computer turns up the idle speed so it thinks it's a two stroke...
I know in theory that a two stroke won't have the engine braking of a 4-stroke, but in the real world of model planes the two stroke (if operating properly) will come down to low idle very quickly when you chop the throttle. They also spool up quickly if you use a light weight prop. Two stroke engines that don't decelerate quickly usually have an air leak (bad bearing seal typical).
In MotoGP, they've figured out a way to eliminate engine braking in a 4-stroke. The engine management computer turns up the idle speed so it thinks it's a two stroke...
