U.S. Spec Monkey Race Exhaust: Full System Upgrade Guide

Quick answer

The Yoshimura Race Straight Cyclone full exhaust system is a direct-fit upgrade for the U.S. spec Honda Monkey (2019-2026). This guide covers the tools, steps, and common pitfalls for a clean installation.

Installation steps

1. 1. Prepare the bike and gather tools: Park the Monkey on a level surface and let the engine cool completely. You will need: a 10mm socket, 12mm socket, 14mm socket, torque wrench, penetrating oil, and a rubber mallet. Wear gloves and eye protection. A cold engine prevents burns and makes gasket removal easier.
2. 2. Remove the stock exhaust system: Loosen the exhaust flange nuts at the cylinder head (10mm) and the muffler mounting bolt (12mm). Spray penetrating oil on the exhaust gasket and header joint. Carefully slide the header out of the cylinder head—do not pry on the studs. Remove the muffler and hanger bracket. If the gasket sticks, use a plastic scraper to avoid damaging the head surface.
3. 3. Install the new exhaust gasket and header: Insert a new exhaust gasket (supplied or OEM) into the cylinder head port. Apply a thin layer of anti-seize to the header pipe's mounting flange. Slide the header into the head and hand-tighten the flange nuts. Do not fully torque yet. A fresh gasket ensures a leak-free seal; reusing the old one can cause exhaust noise and power loss.
4. 4. Mount the muffler and connect the system: Position the muffler on the hanger bracket and loosely install the mounting bolt (12mm). Connect the header-to-muffler joint and tighten the clamp. Align the system so it clears the rear shock and swingarm. Torque the header nuts to 12 ft-lb and the muffler bolt to 18 ft-lb. Check clearance at full suspension compression—rub marks indicate misalignment.
5. 5. Final checks and tuning: Start the engine and let it idle. Listen for exhaust leaks at the header and joints. If the bike runs lean (popping on deceleration), you may need to re-jet the carburetor or add a fuel controller. The Race Straight Cyclone is a full system, so the ECU may need adjustment for optimal performance. A quick test ride under load will reveal any tuning issues; avoid sustained high RPM until the air-fuel ratio is verified.

Product facts

• U.S. SPEC MONKEY 19-26 Race Straight Cyclone Full System Exhaust: The Race Straight Cyclone system weighs only 4.2 pounds. Reducing unsprung weight improves handling and acceleration, making the Monkey feel more responsive.