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Old Feb 15, 2015, 06:35 AM
The Curse of the Flying Scroll
Chophop's Avatar
Pleasant Valley Modelport
Joined Sep 2006
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Wouldn't a reed valve help with the spitting ? I also need to look into the action of back pressure through the carb causing a stir in the carb internals that may take some time to reverse, a cause for rough running.
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Old Feb 15, 2015, 07:44 AM
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Quote:
Originally Posted by earlwb View Post
It should be firing the spark plug on every revolution. I would agree with darkith and double check the battery pack. As soon as the magnet passes the sensor, it should trigger a spark. You can also check the spark plug gap too. Also make sure the spark plug cap is pushed down onto the plug and has a1/4 twist to lock it on. Otherwise it can come loose. usually once the cap locks on, you have a hard time getting it off.
My battery is charged, what should the gap size be?

Thank you for the help!
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Old Feb 15, 2015, 09:17 AM
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Usually the gap is something like .020 to .025 inches.

One thing is that the battery may not be able to provide the power or current needed to run the ignition system. I actually ran into this with some LiFe receiver battery packs. The battery pack would power the radio just fine, but when I started the engine, the radio and servos would quit working. Pretty weird. When I swapped it out for a better battery pack, then everything worked fine. Some other times, the engine would run and idle OK but not run at more than 1/2 throttle without simply dying. It turned out the battery could run the engine at low speed but couldn't provide the power for high speed. Except for the early ignition units that could draw upwards of 1.6 amps, the modern CDI units draw about 650 milli-amps at full throttle, less at idle speed.

You also do not want to see how long of a spark you can get. That increases the voltage tremendously resulting in internal damage to the ignition coil.

ChopHop:
Actually just about all model engines will spit fuel. The more aggressive the port timing there is, the more they spit. Two strokes and four strokes do it. Saito was putting on intake stacks on their four stroke engines to help minimize it. They call it "reversion". You can typically feel it with the front rotary valve intake engines, by holding your hand behind the engine when it is running, little tiny droplets of raw fuel will hit your hand and cool it for a split second. But the spitting is normally not a problem with the engines. It might increase the messiness some though. A short intake stack would alleviate the problem in most cases.
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Last edited by earlwb; Feb 15, 2015 at 09:24 AM. Reason: add more info
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Old Feb 15, 2015, 10:58 AM
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Joined Dec 2014
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Quote:
Originally Posted by earlwb View Post
Usually the gap is something like .020 to .025 inches.

One thing is that the battery may not be able to provide the power or current needed to run the ignition system. I actually ran into this with some LiFe receiver battery packs. The battery pack would power the radio just fine, but when I started the engine, the radio and servos would quit working. Pretty weird. When I swapped it out for a better battery pack, then everything worked fine. Some other times, the engine would run and idle OK but not run at more than 1/2 throttle without simply dying. It turned out the battery could run the engine at low speed but couldn't provide the power for high speed. Except for the early ignition units that could draw upwards of 1.6 amps, the modern CDI units draw about 650 milli-amps at full throttle, less at idle speed.


You also do not want to see how long of a spark you can get. That increases the voltage tremendously resulting in internal damage to the ignition coil.

ChopHop:
Actually just about all model engines will spit fuel. The more aggressive the port timing there is, the more they spit. Two strokes and four strokes do it. Saito was putting on intake stacks on their four stroke engines to help minimize it. They call it "reversion". You can typically feel it with the front rotary valve intake engines, by holding your hand behind the engine when it is running, little tiny droplets of raw fuel will hit your hand and cool it for a split second. But the spitting is normally not a problem with the engines. It might increase the messiness some though. A short intake stack would alleviate the problem in most cases.
I have been running a 2 cell 800mAh lipo regulated to 5 volts for the whole time I have been running. I will check the gap. Thank you for the help!
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Last edited by 3dFlyingMaster; Feb 15, 2015 at 10:59 AM. Reason: Not enough info
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Old Feb 15, 2015, 08:49 PM
The Curse of the Flying Scroll
Chophop's Avatar
Pleasant Valley Modelport
Joined Sep 2006
9,161 Posts
Somewhere maybe this thread brought me to an answer for the 45 cut velocity stack orientation. Some people were saying to run the opening to the rear. That would cause a negative pressure at the carb throat. I run it with the opening forwards and parallel to the general line of the fuselage.

I don't trust that other way.
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