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All Forums >> Glow Engines, Gas Engines, Fuel & Mfg Support Forums >> Glow Engines >> Over proping
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Over proping - 10/3/2002 12:31:18 AM   
Zoned


 

Posts: 102
Joined: 1/5/2002
From: Easton, PA, USA
Status: offline 		Would over proping cause a YS 4 stoke to predetonate at wide open throttle.


Pat
       Post #: 1

Over proping - 10/3/2002 12:43:22 AM   
banktoturn



Posts: 674
Joined: 8/22/2002
From: Bloomington, MN,
Status: offline 		Zoned,

I don't have any direct experience with the model 4-strokes, but the situation you describe is exactly the kind of situation in which an engine is most likely to knock ( or predetonate ). Low speed and high cylinder pressure are the conditions that favor knock, and that is what you get when you over load ( over prop ), and open up the throttle. If my understanding of glow fuel characteristics is correct, using less nitromethane may help.

banktoturn

(in reply to Zoned)
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Over proping - 10/3/2002 1:36:31 AM   
m.gramling



Posts: 1787
Joined: 1/8/2002
From: Atoka, TN, USA
Status: offline 		I think yes. Try going to a smaller prop.
Could try less nitro, could also try using another compression ring under the glowplug,

But I would just find me a prop that would cause your problem.

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Over proping - 10/3/2002 1:37:25 AM   
m.gramling



Posts: 1787
Joined: 1/8/2002
From: Atoka, TN, USA
Status: offline 		Also if its a 2stroke, you could use another headgasket to lower compression.

I don't think you can do that w/ a four stroke though.

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Over proping - 10/3/2002 2:01:01 AM   
w8ye



Posts: 17186
Joined: 12/11/2001
From: Taylortown, OH, USA
Status: online 		You are running your Y-S too lean. That is causing the pre-ignition and the throwing of the prop etc. Open up the needle a little.

Also, if you have a crankcase leak or plugged filter, the mixture can go lean and cause the popping.

Give a few more details?

Good luck,

Jim

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4 stroke - 10/3/2002 2:10:04 AM   
spuck5644



Posts: 276
Joined: 3/19/2002
From: Springfield, IL, USA
Status: offline 		Pat,
You don't give many details, but, I also think you might be a little lean. We have swung as large as an 18x6 on YS-120's w/o problems.

Steve

Puckett Model Aviation

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Over proping - 10/3/2002 6:07:38 AM   
ishu4u


 

Posts: 217
Joined: 1/9/2002
From: frankfort, KY, USA
Status: offline 		th ys engines like the rich side on the ground and unload in the air alot.. some even back fire on the ground..could not believe my ears the first time i heard one do that. but it happens alot and the owners claim to have well over 100 plus flights on them with no trouble. on the other hand i have seen rebuilds at under 100 flights due to lean runs. even just a few lean runs can change the ys engines life quickly. air leaks begin to form and it's down hill from there. stay fat and stay flying

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Over proping - 10/3/2002 7:21:20 AM   
Zoned


 

Posts: 102
Joined: 1/5/2002
From: Easton, PA, USA
Status: offline 		I put new gaskets,diaphram and plunger. I'm using 20/20 fuel and swinging a 15/8 prop. I can open the main needle 3 to 4 turns out and it still does it. The engine is inverted and it is so rich at idle fuel drips out of the carb.It is fine when it is cold then after 1 tanks when the engine is hot thats when the trouble starts. Compared to my other engines the compression seems high even when hot. I might just have to send it in.

Pat

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Over proping - 10/3/2002 8:04:20 AM   
ishu4u


 

Posts: 217
Joined: 1/9/2002
From: frankfort, KY, USA
Status: offline 		i suggest asking if anyone around you has an i4c compression tester and check it after the first flight and compare it to the psi held when cold.. should hold atleast 8psi or else you have a leak somewhere..

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Over proping - 10/3/2002 8:54:59 AM   
w8ye



Posts: 17186
Joined: 12/11/2001
From: Taylortown, OH, USA
Status: online 		I don't believe you ever said which Y-S you have yet?

It would help because there's different ways some of them are made.

But, you have finally showed your hand! And you still have an airleak.

The Y-S 91 has an air chamber on the back of the cylinder. This has a thin paper gasket around it to seal it. But, when you try to put a new one on the box, it is very difficult to do and not have the gasket fall out of place.

You have to undo and raise up the cylinder to attach the box securely with (no leaks) to the back of the cylinder.

Then you put the rubber seal on and insert the cylinder and box together down on the carb.

Being as you had the regulator apart, did you get everything back on in the correct order? BTW the tit on the cover goes towards the front and the adjusting screw should be towards the front.

Good luck

jim

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Original AMA #31261

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Over proping - 10/3/2002 2:09:41 PM   
Zoned


 

Posts: 102
Joined: 1/5/2002
From: Easton, PA, USA
Status: offline 		It is the 91 AC. I put every thing together as per diagram. The assemble went together smoothly and the air box gasket is visible all the way around. The inside is spotless, I see no dirt or fuel residue. I'll send it in for an estimate and let you know what they say.



Pat

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       Post #: 11

Over proping - 10/3/2002 5:52:02 PM   
w8ye



Posts: 17186
Joined: 12/11/2001
From: Taylortown, OH, USA
Status: online 		pat,

I wish you a speedy response and simple solution.

Good luck,

Jim

_____________________________

Attended the CutFinger Institute of DirtNap University for years but never did graduate....

Club Saito Member #7
Original AMA #31261

(in reply to Zoned)
       Post #: 12

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