. Maintaining these requires precise specifications for float height and jetting to ensure smooth throttle response and proper air-fuel mixtures. Technical Specifications According to service data for the Hyosung GV250 Yamaha XJ600 , standard settings are as follows: Specification (GV250) Specification (XJ600 USA) Idle Speed 1,450 – 1,550 RPM 1,200 – 1,300 RPM Float Height 6.2 – 8.2 mm Fuel Level (Wet) 4.0 – 6.0 mm below gasket line #90 (Front) / #87.5 (Rear) Jet Needle 2nd groove Fixed/Non-adjustable
A common starting point is 2 turns out from lightly seated, though this varies by bike model. Key Helpful Resources XJRider Rebuild Guide: The XJRider forum
Hold the rubber up to a bright light to check for microscopic tears or pinholes.
. This service guide summarizes the critical specifications, maintenance procedures, and tuning adjustments required to keep these carburetors functioning optimally. 1. Core Specifications mikuni bds26 service manual
| Symptom | Likely Cause (per manual) | Fix | |---------|---------------------------|-----| | Engine bogs on acceleration | Torn diaphragm or clogged vacuum port | Replace diaphragm, blow out vacuum passage with compressed air | | Black smoke / rich running | Float too high or stuck needle | Reset float height to 15mm, replace needle valve | | Hard starting when cold | Enrichener (choke) plunger not seating | Clean plunger and bore, check O-ring | | Surges at steady throttle | Air leak at carb base or slide guide wear | Replace intake boot gasket, check slide for scratches | | Won’t rev past 4000 RPM | Main jet too small or fuel filter restricted | Upsize main jet by 2 sizes, replace filter |
Drop the float back into position and slide the hinge pin home.
Gently lift the rubber diaphragm to pull out the throttle slide and jet needle. Key Helpful Resources XJRider Rebuild Guide: The XJRider
Pay special attention to the tiny holes near the throttle butterfly valve. These are critical for a steady idle. Step 3: Inspection and Float Height
You will find third-party manuals (e.g., Clymer, Haynes) that cover multiple carburetors including the BDS26. These are acceptable for general procedures but often lack specific data like:
Unscrew the brass needle valve seat from the carburetor body. Inspect the micro-screen filter attached to the back of it for debris. 3. Jet and Emulsion Tube Removal 450 – 1
The Mikuni BDS26 (or BS26) is a 26mm CV (Constant Velocity) double-carburetor setup commonly found on small-to-mid-sized motorcycles and ATVs, notably the Hyosung GV250 and similar 250cc twins. Known for reliability, these carburetors can suffer from performance issues due to neglected maintenance, old fuel, or clogged jets.
Located under the top cap. The rubber diaphragm uses vacuum to lift the slide and needle. The Float Bowl: The bottom chamber where fuel is stored.