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Engine dies when reducuing power from 100%

Old 09-12-2010, 06:59 PM
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spitfire66
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Default Engine dies when reducuing power from 100%

Hello,

I flew my spitfire again and I had success getting off the ground and flying...as long as I didn't back off from full throttle. I got a maximum rpm of 9000 on the ground and leaned to 86-8700 rpm. I then dropped to 1700 rpm and the engine idled at that speed without changing rpm for about 30 seconds. The transition from idle to full throttle is quick, does not hesitate, and sounds like an excellent transition with a little smoke trail. The engine sounds great and feels strong! The problem I am having is in flight when I reduce the engine from full throttle to mid throttle. It just dies. I haven't went to idle with it because it always seems to die in the mid range. I have had to successful dead stick landings and I desperately need advice on what to do. The engine sounds so strong on the ground and tuned to the information I have read provided by two Y.S. online sources. (Troy Newman's info is one source) The diaphram is flush with the housing and I believe it is set, but would try a change if needed. Thanks.

Shannon
Old 09-12-2010, 07:03 PM
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ThumbSkull
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Default RE: Engine dies when reducuing power from 100%

We think it might be a YS from your description, but which one, what prop, what fuel, what plug?
Old 09-12-2010, 07:14 PM
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spitfire66
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Default RE: Engine dies when reducuing power from 100%

Ahh Geez Sorry about that.

Ys 91fz
os type f plug
master airscrew 14 7 3 blade
wildcat 20/20 fuel
1000 feet elevation kansas city mo
Old 09-13-2010, 08:28 AM
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Default RE: Engine dies when reducuing power from 100%

Let's start with the easy things, like changing the glow plug for a new one. If that deasn't help we'll try something else.
Old 09-13-2010, 09:50 AM
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Default RE: Engine dies when reducuing power from 100%


ORIGINAL: spitfire66

Hello,

I flew my spitfire again and I had success getting off the ground and flying...as long as I didn't back off from full throttle. I got a maximum rpm of 9000 on the ground and leaned to 86-8700 rpm. I then dropped to 1700 rpm and the engine idled at that speed without changing rpm for about 30 seconds. The transition from idle to full throttle is quick, does not hesitate, and sounds like an excellent transition with a little smoke trail.
Well this caught my attention and I guess we need some clarification?

"I got a maximum rpm of 9000 on the ground and leaned to 86-8700 rpm."

Did you really reduce the top RPM by leaning the engine?

Then there's this part; "with a little smoke trail."

In my experience, the YS needs a pretty good smoke trail showing or it's too lean but what is the OP's definition of "little smoke trail" vs. my definition needs some clarification as well 'cause right now I'm thinking if the OP has what he's indicated, the little 'fella is too lean and getting hot.
Old 09-13-2010, 10:05 AM
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Default RE: Engine dies when reducuing power from 100%

I have a new glow plug in the engine. I had the engine at YS Parts and Service last december. The engine had new gaskets and bearing installed and was said to be good to go. However the carb does drip a little fuel when not running. Everything else looks good.
Old 09-13-2010, 03:26 PM
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Default RE: Engine dies when reducuing power from 100%

I have so much going through my mind I need to read and re-read.

I enrichened 300 rich of peak at going from 9000 to 87-8800 rpm.

I have the low end set at 1700 rpm where it is idleing steady.

I am having problem with the mid range. I just ran the thing about 30 seconds ago and jumped on here to type before I forget valuable info. I am taching the mid range right now and I set 4000 rpm and let it sit without throttle adjustment. At first it sits at 4000 rpm, then slowly creeps to a high of 4400 rpm. Upon reaching 4400 rpm the engine sounds like it weakens and then drops to 2800 rpm and runs blubberishly for a second and then goes back to 4000 rpm. The engine does not die, but rather repeats the process. Is the engine in need of regulator adjustment?
Old 09-13-2010, 06:42 PM
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Default RE: Engine dies when reducuing power from 100%


ORIGINAL: spitfire66

I have a new glow plug in the engine. I had the engine at YS Parts and Service last december. The engine had new gaskets and bearing installed and was said to be good to go. However the carb does drip a little fuel when not running. Everything else looks good.
If you are dripping fuel the regulator is being held open by either trash in the regulator or the spring is getting weak. If you are comfortable with taking the regulator apart, I'd start there. It doesn't take much dirt to cause a lot of grief for the regulator and the operator.
Old 09-13-2010, 07:42 PM
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spitfire66
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Default RE: Engine dies when reducuing power from 100%

I ran a couple test runs/tuning runs today and cleaned the regulator before hand. The carb is not dripping anymore what so ever. The only problem I am having now is with the midrange surging as described earlier. It goes from 4000 to 4400 then drops to 2800 and then back up to 4000 without dying.
Old 09-14-2010, 07:18 AM
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Default RE: Engine dies when reducuing power from 100%

If the midrange is creeping up and then dropping it sounds like it's lean and getting hot.. Richen the regulator in 1/8th turn increments until the midrange settles down. It shouldn't take much.
Old 09-14-2010, 08:37 AM
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Default RE: Engine dies when reducuing power from 100%

I will try enrichening the regulator more. I am a little over flush right now (regulator screwed out). I will try tomorro when I have a little time.
Old 09-15-2010, 03:46 PM
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Default RE: Engine dies when reducuing power from 100%

I have it figured out now. The regulator was way too lean, and when I was trying to tune the first time I was running the engine on the ground too long. This time I was sure to let the engine warm up for 45 seconds then run the engine while tuning no more than 3 minutes for one period, followed by a 5 minute cool down. I was reading that most have the regulator set flush with the housing but found mine needed to be about 1/2 to 3/4 turn out from the housing. I then retuned and was getting a peak rpm of 9300, then I set it rich at 9000. The mid range is holding 4000 fairly steady with only a 100-200 rpm twitch. The low end is holding 1800.

Lesson learned: 1. Don't let it run on the ground long or else the heat becomes your enemy.
2. Set the regulator rich and work on going lean, rather than the other way around

Thanks for the help. Maybe someone else can learn from this as well!

YS POWER BABY!
Old 09-15-2010, 08:46 PM
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Default RE: Engine dies when reducuing power from 100%

That is great to hear. It's always nice to hear when someone gets their enige figured out.

A lot of people think that the regulator should be flush because most wind up in that vicinity BUT each engine is slightly different due to fuel, atmospherics, prop....ect...you get the point. The important thing is exactly what you learned, listen to the engine and give it what is asking for.

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