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Old 12-23-2006, 03:24 PM   #1
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Default MR Ninja MR21 B01 engine Idling high after throttle input?

My .21 Ninja engine idles high for 2-4 seconds after applying, running around, and releasing the throttle, and then it will settle to its normal idle tone after. Itís idling the same way as if you were pinching the fuel line to the carb to kill the engine.

I've tried messing with the idle screw, LSN, HSN, changing plugs (mid plugs). It wasn't doing this the other day when the ambient temperature was about 70 deg; today it was about 80 deg. Iím not sure if the ambient temp is affecting anything to do with this.

I also have an inline fuel filter before the carb that I've noticed sometimes will trap small bubbles of air in it.

Any recommendations? Thanks for the help.
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Old 12-23-2006, 04:16 PM   #2
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Is the fuel filter installed correctly? If installed backwards, it will restrict flow.

Other than that, it sounds like your LSN is lean. Ive had this problem before and I thought it was a leak. I sealed everything and it kept happening. I returned all the needles to the factory setting and while I was doing that, my LSN was way to lean.
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Old 12-23-2006, 04:46 PM   #3
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Richen up the low end for it's a little lean. Seeing you don't have a mid to play with this is the only thing you can do.
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Old 12-23-2006, 11:06 PM   #4
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I did try in richening the LSN and it was causing the engine to bog and die during launch.
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Old 12-24-2006, 05:34 AM   #5
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You must richen your lsn, but when you make this adjustment increase your idle screw as well, just a bit at a time.
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Old 12-24-2006, 09:16 AM   #6
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did you put a small amount of sealer around your carb on install? how much air was in the filter? check to make sure your fuel feed where your fuel line hooks to the carb is snug. do not overtighten that!... make sure your plug is good. and then retune
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Old 12-25-2006, 05:52 PM   #7
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I had motors do this when they are not warmed up to operating temp after I raced a few laps the idle was good. high idle is normal with some engines.
the ones I had that did that were 5port novas
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Old 12-25-2006, 07:19 PM   #8
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This is the same problem I was having when I got into 1/8 racing. It drove me nuts trying to tune the engine, but in the end it wasn't the engine. No mater how you tune, you should always keep your idle to where the carb is open CLOSE to 1 mm at idle. If you have to open the idle to run it rich it defeats the purpose. Anyway, here is what was happening on my car.

After clearing out the engine, it would take a while to get to proper idle, but keeping on richening the bottom would make it sluggish and it would load up real bad, but not fix the high reving upon deceleration.

In the end it was the clutches keeping the engine wound up. The clucthes had to much wear and also a too soft of spring. A stiffer clutch spring helped disengage the clutch thus letting the motor rev back down. Take a look at that.
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Old 12-26-2006, 03:49 PM   #9
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Default Carb tuning

I have had this happen before i learned how to adjust the carb . Your low speed is not too lean. It is your high speed needle. More than likely your low speed needle is rich and the high speed is too lean so when you give it throttle it will use up the extra fuel and it starts leaning out then when you go back to idle it is high till it starts loading up with fuel. You should allways tune the idle before tuning the high speed needle. If you go to cefx.net there is a great carb tuning section. Hope this helps
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Old 01-22-2007, 03:07 AM   #10
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ninja carbys have a burr in the throttle body it will go away after a while or you can disasemble it your self and deburr even the new a spec does it bloody quick motor but
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