Aprilia RS 125 carb set up , how do you do the plug chop , test engine running conditions RS 125

Aprilia RS125 workshop manual for sale Ebay UK 

Aprilia RS125: How to Perform a Plug Chop

A "plug chop" is the only accurate way to check your carburetor jetting at wide-open throttle (WOT) to prevent a high-speed engine seizure on a Rotax 122/123.

• The Preparation: You must use a brand new spark plug (NGK BR10EG/EIX). An old, carbon-fouled plug will not show the new combustion "color" accurately.

• The Procedure:

  1. Warm the engine up on an old plug first.

  2. Install the new plug and find a long, safe stretch of road.

  3. Accelerate through the gears to 6th gear at wide-open throttle.

  4. Hold the engine at peak RPM (approx. 10,500–11,000) for 10–15 seconds.

  5. The Chop: Simultaneously pull the clutch in and hit the kill switch. Do not let the engine idle or coast in gear, as this will "overwrite" the high-speed reading.

• Reading the "Smoke Ring": Remove the plug and look at the porcelain insulator base:

  • Coffee Brown: Perfect main jetting.

  • White/Grey: Dangerously lean (Increase main jet size immediately).

  • Black/Oily: Too rich (Decrease main jet size).

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Aprilia RS125 Plug Chop Guide: How to tune Rotax 122 main jets. Learn the 6th gear kill-switch method to read spark plug color and prevent seizures.

Aprilia RS 125 Plug Chop

Basically a plug chop involves putting the bike under load at high revs

 Chopping is where the ignition is cut at a certain RPM while the engine is under load

 Hit the kill switch and pull clutch in fast , Slow down and with gloves on remove  spark plug (hot).

the plug will have a colour which can be checked to given running conditions inside the cylinder at what every RPM or throttle position you did the run at . ie third , half full throttle or certain rev ranges .

Black = rich

Brown = good

Grey / white = dangerous conditions

for advice on jetting and which jets to use see here 


CARB SETUP
Set it to rev at 2000 with the idle screw, then twiddle the air screw just to the left of the idle screw... turn it all the way in, then back out 1.5 to 2.5 turns, listening to engine. As you turn it, revs should increase slightly. Set it to a point that revs are at highest and smoothest. Now use the idle screw to tune it back down to around 1100rpm ( i normally set mine at 1500rpm )... that should be the carb as set as it can be. 
                                                               
                                 

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