APRILIA RS 125 : Aprilia RS 125 carb jetting jets 28mm 34mm RS125

Aprilia RS 125 parts for sale on Ebay UK

Aprilia RS125 workshop manual for sale Ebay UK

Aprilia RS125 Carburetor Jetting Guide

Choosing between the standard Dell'Orto PHBH/VHST 28mm and the upgrade VHSB 34mm is a balance between low-end rideability and top-end scream.

1. Dell’Orto 28mm (Standard/Full Power)

Best for city riding and reliability. It offers a crisper throttle response at lower RPMs.

Main Jet: Typically 115–125 (Stock de-restricted).
Needle: X2 (usually on the 2nd or 3rd notch from top).
Pilot/Idle Jet: 62–65.
Note: If you install an Arrow or Giannelli exhaust, you may need to go up to a 128 or 130 main jet to avoid running lean.

2. Dell’Orto 34mm (The "Flat Slide" Upgrade)

Found on older "Extrema" models and used for track-ready performance. It increases top-end power but can be "boggy" if not jetted perfectly.

Main Jet: 155–160 (Standard starting point).
Needle: K57 is standard; however, many tuners swap to a K21 to lean out the 5,000–6,000 RPM "stutter" common on the RS125.
Idle Jet: 36 or 38 (B36/B38).
Atomizer: DP266 or DQ266.
Warning: The 34mm uses a different intake manifold and throttle cable than the 28mm. Do not try to force it into the 28mm rubber boot.

A simple equation for figuring you main jet is to multiply dia of carb by 5 and then multiply buy 0.85 for stock 0.9 for bike with sports airfilter fitted 0.95 for airfilter and exhaust .

28 x 5 x any of 0.85 - 0.90 - 0.95

Aprilia rs125 carb jetting 34mm and 28mm

Aprilia RS 125 carb jetting jets 28mm 34mm RS125

Aprilia rs125 28mm carb on Ebay UK here

Aprilia rs125 carb jets on Ebay Uk here

Dellorto PHBH28BD standard

you do not need to re-jet for derestriction but its always advisable after any change to do a plug chop test to test combustion conditions , this will give a clear indication of the jetting and running condition inside the cylinder , also its recommended to increase jets size 5 points for any sports airfilter or exhaust fitted and again do the plug chop test to ensure correct running conditions this is a good habit to get into after doing any work on your bike that may after fuelling .

starter jet 70

main jet 120

pilot jet 62

slide needle valve bn266

float needle valve 250

Dellorto 34mm for sale here on Ebay UK

1. choke jet

2. main jet
3. float
4. atomiser
5. idle tube / pilot jet < same thing
7. needle valve and seat
8.main jet anti surge washer
air fuel is the angled screw towards the air box and is a air screw (not the one with the spring on thats the idle screw)
out =more air to fuel
in = less air to fuel
float height set at 14mm dellorto suggest 11 mm i ran 14mm tho

155 main

36 idle jet

1.5 turns out on the air screw

60 choke jet

k57 needle top notch

app 266 needle jet / atomiser

The purpose of the carburettor is to provide your engine with the correct ratio of fuel and air. Although the carburettor can’t provide the ideal mixture at all loads, the different parts of the carburettor work to try and create this ideal mixture for proper combustion.