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Old 04-09-2013, 01:42 AM   #1
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Default RB concept tuning problem

Can anyone help me I have a RB .12 motor that runs for about a minute and then just dies to a idle speed no matter where the throttle position is then as I was try ing different things I noticed that as soon as I opened the fuel cap on tank the motor revved normally so I then tried
without line from exhaust to tank and it actually run really hard but then I stopped it as it was lean. Has anyone come across this situation
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Old 04-09-2013, 08:58 AM   #2
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Its difficult where your idle speed is set. Your LSN maybe lean, check by turning it CW slowly, if idle speed, dies, its definitely lean. Idle speed should drop to where you set it, then drop in rpm 5second later. If you are patient you can get where your comfortable. you can get it to idle 45-1hr it you want it to. You can get your LSN to drop 1 second from idle speed to drop. Turn your LSN you will hear it idle drop. Going it CW idle increases lean. You may like to be a little rich at idle speed, it wont have that flat spot most engine have. just be patient.
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Old 04-09-2013, 02:22 PM   #3
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it seems your exhaust pressure hose is blocked.
Pry open the exhaust pressure nipple with a needle or a wire.
Blow on the pressure hose with the carb hose disconnected and see if the fuel comes out freely. it may be blocked in the tank cap.

good luck.
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Old 04-09-2013, 02:51 PM   #4
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If the engine runs good for a minute then starts bogging you are too lean somewhere. It could be either needle or both.

Also check your pressure nipple on the pipe as previously suggested. It won't hurt to check your fuel lines and tank for cracks or leaks as well.

I would guess its a tuning issue since it runs normally on startup. If it ran slow at all times I would guess it was fuel system related.
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Old 04-09-2013, 04:41 PM   #5
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Quote:
Originally Posted by bradt View Post
Can anyone help me I have a RB .12 motor that runs for about a minute and then just dies to a idle speed no matter where the throttle position is then as I was try ing different things I noticed that as soon as I opened the fuel cap on tank the motor revved normally so I then tried
without line from exhaust to tank and it actually run really hard but then I stopped it as it was lean. Has anyone come across this situation
First, as suggested check for any blockage on your pressure line then reset your needles LSN 2.5 turns out HSN 4.75 turns out. Go from there fine tuning accordingly idle speed on bench and the on the track.

regards
AFM
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Old 04-12-2013, 04:20 AM   #6
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Thank you for your suggestions will try them all on the weekend
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