TM38-18, 38mm TMX Mikuni 2 Stroke Racing Carb (47mm Spigot)

TM38-18, 38mm TMX Mikuni 2 Stroke Racing Carb (47mm Spigot) | Kawasaki | Yamaha | Suzuki | Honda | 2 Stroke Engines

The Mikuni TM38-18 38mm TMX Flatslide Carburetor is a premium racing carburetor engineered for high-performance 2-stroke engines, excelling on 250cc reed valve motors, larger 2-strokes, and even later-model 125cc motocross engines (Kawasaki, Yamaha, Suzuki, Honda, KTM, and more). It also suits many bigger displacement 2-strokes with minimal or no jet changes.

This genuine factory racing TMX variant is considered one of the best-performing versions ever made—unrestricted by the modifications found in many OEM pollution-compliant carbs.

Key Features

• Flat slide in a smooth-bore venturi for superior throttle response and a wider, more usable powerband.
• Independent twin-float system with a main jet housed in a baffled chamber delivers smooth, hesitation-free performance on the roughest terrain and during aggressive riding.
• "Dramastically" reduces common OEM carb issues like hesitation, hard starting, bogging, and flat spots—while significantly boosting overall power and reliability.
• Note for piston-port engines: Requires a substantial jetting reduction (leaner settings) compared to reed-valve setups.

Factory Jetting (Installed)

• Pilot Jet: 20 (VM22/210)
• Jet Needle: 6EJ12-55 (leaner and richer options available)
• Needle Jet: Fixed (non-replaceable)
• Main Jet: 370 (4/042 series)
• Throttle Slide: 3.5 cutaway (999-832-014)

Dimensions

• A (engine-side spigot OD): 47mm
• B (depth/front-to-back): 76mm
• C (height): 164mm
• D (air-box side OD): 62mm
• Total Width: 76mm

Tuning Recommendations

The stock jetting is excellent for most applications—especially 250cc reed-valve and larger 2-strokes—often requiring only minor tweaks:

• Main Jet: Verify optimal wide-open throttle (WOT) mixture and peak power by testing spares—one size richer (380) and one leaner (360).
• Pilot Jet: Usually spot-on with 20; after setup and checking idle/transition, some engines (e.g., many Huskys) prefer a leaner 25, or occasionally one/two sizes leaner.
• Jet Needle: Rarely needs replacement except in certain multi-cylinder setups. The 6EJ12-55 is a strong baseline.

E-Clip Position on the Jet Needle Adjusts the air/fuel ratio mainly from ¼ to ¾ throttle:

• Lower the clip (raises the needle) → richer mixture.
• Raise the clip (lowers the needle) → leaner mixture.

Changing the Jet Needle Fine-tunes the ⅛ to ¼ throttle range if needed. The stamped number (e.g., 55 in 6EJ12-55) indicates the straight-section OD in hundredths of a mm (2.55mm here).

• Smaller OD number → richer mixture.
• Larger OD number → leaner mixture.

Always follow the included tuning sheets for step-by-step optimization—dialing in perfect performance is straightforward with this carb.

Installation Notes

• If your existing carb is ~12mm, 20mm, or 40mm longer than the TMX's 76mm depth, and you're retaining the stock airbox, add a matching silver anodized extender (available separately on the TMX Carbs page). The 12mm/20mm extenders have a 60mm OD at the airbox end (slightly undersized); the 40mm extender is 62mm OD. Include in order comments if you'd like it press-fitted with Loctite prior to shipping.
• Throttle cable: The reference photo shows minimum inner cable protrusion and fitting at the carb end (backboard marked in 1mm/10mm increments). If your cable is too short, consider a quick-action throttle/cable kit.
• Replacing carbs with TPS (throttle position sensor) or other electronics? Confirm if those connections are required before installation.

Ordering Information

Please provide in your order notes:

• Year, make, and model of your bike
• Exhaust type (stock or aftermarket)
• Any engine modifications
• Intended use (street, trail, or track/race)

This carb offers proven race-level performance, crisp response, and rock-solid reliability for demanding 2-stroke applications. Questions? Contact us