Royal Enfield 570836/B – Needle Assembly (Jet Needle 1.5, BS29 CV Carb) for Classic 350, Bullet 350 UCE, Electra 350, Thunderbird 350

The Royal Enfield 570836/B Needle Assembly is the genuine jet needle assembly (1.5) used in the BS29 CV carburettor on a wide range of Royal Enfield 350cc and Machismo models. Official Thunderbird 350/500 parts catalogues list “570836/B – Needle Assy. 1.5 (BS29)” in the CV carburettor section, confirming its role as the slide/jet needle rather than a float needle.

Reputed OE sellers describe this part simply as “Needle Assembly” or “Needle Valve Assembly – 570836”, under Classic 350 carburettor assembly and Thunderbird 350 / Bullet 350 categories, while  Classic 350, Bullet 350 UCE (KS/ES), Electra 350 UCE (ES), Thunderbird 350/TBTS, Machismo A350 (1999), Thunderbird KS (CDI 2004 / TCI 2005) and Thunderbird ES (2005). 

This jet needle controls the mid-range fuel mixture in your BS29 CV carb. A worn needle or needle jet can cause flat spots, poor pick-up, surging and high fuel consumption. Replacing the jet needle with a genuine 570836/B restores proper taper and height, helping your Classic / Bullet / Electra / Thunderbird / Machismo run smoother through the mid-rpm range.

Ideal when doing a full carb overhaul, resolving tuning issues after high mileage, or restoring an older Machismo/Thunderbird to factory fuelling, this is a direct OEM replacement—no guesswork, no local pattern parts.

Key Features 

• Genuine Royal Enfield part – Officially listed as 570836/B – Needle Assembly in Royal Enfield parts databases and microfiche.

• BS29 CV carb jet needle (1.5) – Correct needle profile for the BS29 CV carburettor used on multiple 350cc and Machismo models.

• Wide model coverage – Trusted suppliers map 570836/B to Classic 350, Bullet 350 UCE KS/ES, Electra 350 UCE ES, Thunderbird 350/TBTS/X350, Machismo A350, Machismo A500 and older Thunderbird KS/ES.

• Restores mid-range fuelling – Corrects taper and height for smoother acceleration, better throttle response and reduced flat spots.

• OEM-grade machining and finish – Ensures proper fit in the slide and needle jet, unlike cheap pattern needles that wear quickly or upset mixture.

• Direct replacement – Drop-in fit for BS29 carb; no modification required when replacing a worn jet needle.

• Carburettor-specific spare – Listed under Carburetor Assembly – Classic 350 and Thunderbird 350 categories by OE sellers.

Compatibility Table 

CHECK PART NUMBER BEFORE PURCHASE 

Explicitly NOT listed / we treat as incompatible:

• J-Series models – Classic 350 J, Bullet 350 J, Meteor 350, Hunter 350 (EFI throttle body, no BS29 carb).

• 650 Twins – Interceptor 650, Continental GT 650, Super Meteor 650, Shotgun 650 (EFI).

• Himalayan / Scram 411, Himalayan 450 / Guerrilla 450 (different carb/EFI).

• EFI 500s – Classic 500 / Bullet 500 / Thunderbird 500 EFI (UCD33 system, no BS29 jet needle).

Variants

• Single OEM variant:

  • Part Number: 570836/B

  • Description (OE): Needle Assembly 1.5 – BS29 CV Carb

No LH/RH, colour or size variants.

FAQs 

Q1. Is 570836/B a float needle or the main jet needle?
A1. 570836/B is the jet needle assembly (Needle Assy. 1.5) for the BS29 CV carburettor. It controls mixture in the mid-throttle range. The float needle/float assembly is a different part number (e.g., 500843) and is not included here.

Q2. Which bikes does this needle assembly fit?
A2. Multiple trusted sources confirm fitment on Classic 350 (carb), Bullet 350 UCE (KS/ES), Electra 350 UCE (ES), Thunderbird 350/TBTS/X350, Machismo A350, Machismo A500 and early Thunderbird KS/ES (2002–2005) that use the BS29 CV carb.

Q3. Does it fit the new BS6 Classic 350 J-Series or EFI 500 models?
A3. No. The BS6 J-Series bikes use EFI throttle bodies, and the 500 EFI models use the Keihin UCD33 system. They do not use the BS29 CV carb, so 570836/B is not applicable.

Q4. When should I replace the jet needle?
A4. Replace the needle if you see visible wear marks/steps on the taper, experience flat spots or surging at mid-throttle, or if mixture tuning cannot be stabilised even after cleaning jets and setting float height. A fresh OEM needle helps restore correct fuelling.

Q5. Can I use this with aftermarket jets or performance carb kits?
A5. 570836/B is designed around the stock BS29 CV carb and OEM jetting. Many tuners still use it with slightly altered jet sizes, but for race/performance setups you should follow the carb kit supplier’s recommendations.