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YS91 questions - 9/12/2002 10:06:05 PM   
BocaBen


 

Posts: 161
Joined: 4/12/2002
From: Boca Raton, FL, USA
Status: offline 		Some quick questions for the YS guru out there:

- The low end idle screw instruction says that to lean, it should be turned CCW (reverse than normal). Looking into the carb. barrel, that low end screw is closing a hole when turning CW in the secondary flap. How can closing this hole mean getting the mixing richer?? I don't get the rationale??

- The body says 91AC but the engine is brand new. I thought that only the 91FZ was available. What is the difference between the 91AC and 91FZ?

Thanks
Ben
       Post #: 1

YS91 questions - 9/12/2002 10:11:52 PM   
MinnFlyer



Posts: 19375
Joined: 4/22/2002
From: Willmar, MN, USA
Status: offline 		The hole is an air bleed. By closing it, you are cutting off the air supply, hence, making the mixture richer. Sorry, I can't answer the second half of your question.

_____________________________

Mike B.
AMA# 42400 www.gettingairborne.com

"Those are my principles. If you don't like them, I have others." - Groucho Marx

(in reply to BocaBen)
       Post #: 2

YS91 questions - 9/12/2002 10:56:01 PM   
azhar


 

Posts: 571
Joined: 2/21/2002
From: Redmond, WA, USA
Status: offline 		The 91 AC and FZ share the same body. The difference will be the carbuerator housing and a slight head design difference I think.


Azhar

(in reply to BocaBen)
       Post #: 3

YS91 questions - 9/12/2002 11:06:15 PM   
w8ye



Posts: 17302
Joined: 12/11/2001
From: Taylortown, OH, USA
Status: offline 		To positively identify your engine as an FZ instead of an AC is to look at the prop drive hub. The AC has a keyed prop drive washer. The FZ has a Tapered collet system with no key way on the crankshaft.... The previous posts are correct in what they say about the FZ and I cannot add anymore to their comments.

There's at least three variations of the motor that is referred to as the AC, but I won't get into that.

I found this out by asking the very same question you did at Toledo at the model show. Dave Shadel himself gave me all the answers that you have recieved here.

enjoy,

Jim

_____________________________

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

Club Saito Member #7
Original AMA #31261

(in reply to BocaBen)
       Post #: 4

YS91 questions - 9/13/2002 5:25:42 PM   
BocaBen


 

Posts: 161
Joined: 4/12/2002
From: Boca Raton, FL, USA
Status: offline 		Thanks all to your answer, I'm now OK with the AC to FZ stuff but still unclear on how closing the hole in the low end adjustment (CW turn of the low end) can make it richer.

MinnFlyer, you say that it reduces the air supply, therefore makes it richer. That would be OK for me if the fuel and air were still separated, but that hole is located between the crankcase and the chamber, which means that fuel and air are already mixed at that point, right? Closing the hole will reduce the fuel/air mix flow to the chamber at idle, and I don't get how that can make it richer.

Thanks
Ben

(in reply to BocaBen)
       Post #: 5

Air bleed control - 9/13/2002 6:15:44 PM   
Hobbsy



Posts: 10555
Joined: 12/2/2001
From: Colonial Beach, VA, USA
Status: offline 		It regulates additional air being admitted into the fuel air mixture, which beyond a certain amount of throttle opening is insignificant, therefore only effective at low speeds.

_____________________________

"I have gone faster backwards, upside down and on fire than most people have gone at all" Don Garlits

(in reply to BocaBen)
       Post #: 6

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