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Tom Jones
Joined: 12 Mar 2006
Posts: 752
Location: Ellensburg, WA
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 Posted: Wed Apr 11, 2007 5:37 am Post subject: Carb slide position at full throttle on a two stroke Rotax |
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The slide valve piston in the Bing 54 Carb has a tang with a little window on the manifold side that hangs lower in the venturi by a few milimeters than the air cleaner side of the piston does. At full throttle should that tang be completly up out of the venturi?
The instructions I have say adjust it so that the slide valve is completly at the top of the venturi. The drawing along with the instructions shows the air cleaner side completly at the top of the venturi but the tang hanging down a couple milimeters into the venturi. How are some of you running?
Tom Jones
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dosmythe(at)cox.net
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| Posted: Wed Apr 11, 2007 11:19 am Post subject: Carb slide position at full throttle on a two stroke Rotax |
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Tom,
I adjust my carb heights so when the throttle is fully open and against
the metal to metal stops on the throttle there is about 1/16" slop on the
cables on top of the carbs. This prevents you from slamming the throttle
wide open and placing tension on the small ball on the end of the cable
(carb end). This will put the slides all the way up except for the 1/16"
mentioned. With this setup I'm almost certain that the slides are
completely up and out of the venturi. As I said, this procedure allows the
metal to metal contact at the throttle just before (1/16") reaching the end
of the slide travel.
Don Smythe
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Tom Jones
Joined: 12 Mar 2006
Posts: 752
Location: Ellensburg, WA
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| Posted: Thu Apr 12, 2007 7:29 am Post subject: Re: Carb slide position at full throttle on a two stroke Rot |
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| Quote: | | The instructions I have say adjust it so that the slide valve is completly at the top of the venturi. The drawing along with the instructions shows the air cleaner side completly at the top of the venturi but the tang hanging down a couple milimeters into the venturi. How are some of you running? |
Here's some more on this. My bing 54 carb throttles were adjusted so that the hanging down part of the slide was even with the top of the venturi which put the air cleaner side of the slide a few milimeters above the top of the venturi. There was a little free play left in the throttle cable when the stop was contacted at full throttle so no strain on the throttle cable ends.
I have the Arctic Sparrow adjustable needles and they would not turn at full throttle...not that they need to be adjusted at full throttle...but this was telling me there was some kind of strain going on with the sparrow needle cables with this setting.
I called CPS yesterday to get their expert opinion as something seemed to not be right. His answer couldn't have been more vague. I still didn't know the answer after talking with them.
I then adjusted the throttle cable so that the air cleaner side of the slide was even with the top of the venturi and the manifold side is hanging down into it a few milimeters. I get the same static RPMs (6200) as before and the sparrow needle cables will turn at all throttle settings. The Rotax manuals seem to lose something...okay, a lot...in the translation.
Tom Jones
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davef(at)cfisher.com
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| Posted: Thu Apr 12, 2007 7:51 am Post subject: Carb slide position at full throttle on a two stroke Rotax |
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Tom,
The artic sparrow needles are silver soldered onto the thread. Is it
possible that they are hitting the top?
If you slides are opening all the way and both carbs are synced You are
likely ok.
The higher your slides go the higher your needles go and come out of the
main jet.
Are you EGTs reading ok in cruise ? And do the spark plugs indicate a good
fuel burn ? Do you have a fuel flow meter? If so what is your readings
are different rpms ?
Your prop might be set properly here and you would not get more rpm with
even bigger jetting as the next obstacle is your exhaust which is timing
your exhaust pulse and allowing for only so much scavenging right now. Hey
you can get 100 HP out of a 582 but it will be in a narrow power band and
you will use alot more fuel and have less reliability.
Dave
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Tom Jones
Joined: 12 Mar 2006
Posts: 752
Location: Ellensburg, WA
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| Posted: Thu Apr 12, 2007 11:02 am Post subject: Re: Carb slide position at full throttle on a two stroke Rot |
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Dave, the EGts are in the green and even with each other. By my calculations and verified by EGts I would say the engine is completely up on the main jets at just under 3/4 throttle and 4800-5000 RPM range. The 503 seems to have plenty of power. Much more than I expected.
I am just trying to figure out if there is a reason the CPS carb set up instructions show a drawing of the carb with the window skirt on the manifold side of the slide valve hanging down into the venturi at full throttle. Does it serve a purpose that isn't obvious to me?
Tom Jones
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davef(at)cfisher.com
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| Posted: Thu Apr 12, 2007 4:00 pm Post subject: Carb slide position at full throttle on a two stroke Rotax |
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Tom,
I looked this up and it concurs with what Don said, I agree open it up all
the way.
Dave
PS EGT gauge is a gauge of what is going on realitime but the spark plugs
will tell the story for real.
http://www.ultralightnews.com/enginetroublshooting/techtips/techtips1.htm
Next have someone apply throttle SLOWLY while you watch the slides. The
slides should BOTH start up at the same time. If not adjust using the two
adjusters located at the top of the carb.
Once you have them starting up at the same time open them all the way up and
make sure that the slide is completely clear at its upper most throttle
position. You now know you have both carbs starting at the same time and
that they are both opening up to full throttle.
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