04-12-2003, 03:26 AM
#1
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The only trick is in having exactly the right amount of prime and having it distributed just right through the engine. There's no point in priming an engine and just letting the fuel sit around inside the crankcase (this is for an upright engine, inverted needs a slightly different technique but the end result is the same).
The first thing is that the needle should never be touched, if it was running OK the last time then it'll run OK the next. I prime with the throttle full open so the low speed doesn't restrict the fuel. I'll give one or maybe two slow turns of the prop to draw a little fuel in then flick as though I'm trying to start it. This throws the fuel from the crankcase up into the cylinder and gets the piston/liner wet and loose. If after maybe 5 or 6 flicks it still doesn't sound wet, give it another prime and try again. As soon as the prop starts to oscillate a little then it should be wet enough to start. Close the throttle, hook up the plug and wait a few seconds for it to heat up and burn off any excess fuel that might have collected inside it. If you want, grasp the prop and turn it over and you should feel a bump as part of the mixture fires. That's a sure sign it's ready to go
Most likely the amount of prime will be different after the first start of the day, in most cases none at all other than getting fuel up to the carb. But if you're doing your first start on a very cold day then you might find that the engine will burp and stop a few times until it gets a bit of heat in it.
The first thing is that the needle should never be touched, if it was running OK the last time then it'll run OK the next. I prime with the throttle full open so the low speed doesn't restrict the fuel. I'll give one or maybe two slow turns of the prop to draw a little fuel in then flick as though I'm trying to start it. This throws the fuel from the crankcase up into the cylinder and gets the piston/liner wet and loose. If after maybe 5 or 6 flicks it still doesn't sound wet, give it another prime and try again. As soon as the prop starts to oscillate a little then it should be wet enough to start. Close the throttle, hook up the plug and wait a few seconds for it to heat up and burn off any excess fuel that might have collected inside it. If you want, grasp the prop and turn it over and you should feel a bump as part of the mixture fires. That's a sure sign it's ready to go
Most likely the amount of prime will be different after the first start of the day, in most cases none at all other than getting fuel up to the carb. But if you're doing your first start on a very cold day then you might find that the engine will burp and stop a few times until it gets a bit of heat in it.
04-12-2003, 10:49 AM
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You may not need to richen the needle before every start. However, just because it starts and appears to be running does not mean it doesn't need adjustment.
Before every flight, do a quick check and pinch the fuel line going to the carb while engine is running at full throttle. What you are doing is verifying your needle setting for the current atmospheric conditions. Our carbs do not adjust for changes in temperature, humidity, barometric pressure/density altitude.
When you briefly pinch and release the fuel line, the engine should noticeably speed up and then back down. It should speed up about 300-400 rpm (use a calibrated ear). If it sounds like it is speeding up too much, then lean it out a bit, if it doesn't speed up or dies, richen it up several clicks.
This takes 5 seconds to do and verify your carb setting. Not a lot of time to ensure you won't fry an expensive engine due to a lean run.
I never set and forget it because engine vibrations can cause a needle valve to change its settings, different fuels change mixtures, different glow plugs affect mixture setting, and of course the previously mentioned weather changes/conditions.
Before every flight, do a quick check and pinch the fuel line going to the carb while engine is running at full throttle. What you are doing is verifying your needle setting for the current atmospheric conditions. Our carbs do not adjust for changes in temperature, humidity, barometric pressure/density altitude.
When you briefly pinch and release the fuel line, the engine should noticeably speed up and then back down. It should speed up about 300-400 rpm (use a calibrated ear). If it sounds like it is speeding up too much, then lean it out a bit, if it doesn't speed up or dies, richen it up several clicks.
This takes 5 seconds to do and verify your carb setting. Not a lot of time to ensure you won't fry an expensive engine due to a lean run.
I never set and forget it because engine vibrations can cause a needle valve to change its settings, different fuels change mixtures, different glow plugs affect mixture setting, and of course the previously mentioned weather changes/conditions.
