Yamaha G1 Carburetor Adjustment & Settings

The Yamaha G1 uses a Mikuni BV21-161 carburetor with a 1-3/8-turn pilot-screw baseline, 18 mm float height and 1200 rpm idle with the V-belt removed. With the belt fitted, the idle target is 1000 rpm.

Yamaha Carburetor Guide

G1 • Adjustment & settings

Carbureted gasoline version.Applies to

Yamaha 2-stroke gasolineEngine

1200 rpm with V-belt removed; 1000 rpm with belt installedIdle

Pilot screw baseline: 1-3/8 turns outMixture

G1 carburetor setup at a glance

Model-specific setup

The G1 service manual publishes a Mikuni BV21-161 carburetor, 1-3/8-turn pilot screw baseline, 18 mm float height and 1200 rpm idle with the belt removed (1000 rpm with belt fitted).

Carburetor: Mikuni BV21-161

Before adjusting

This page covers the carbureted gasoline version. Confirm the engine and carburetor match this setup before using any setting below.

VehicleYamaha G1

EngineYamaha 2-stroke gasoline.

CarburetorMikuni BV21-161.

Idle speed

1200 rpm with V-belt removed; 1000 rpm with belt installed

Pilot / mixture

Pilot screw baseline: 1-3/8 turns out

Float level

18 mm (0.7 in)

Choke

1 mm (0.04 in) choke-cable free play

Governor / linkage

Keep the factory governor and linkage setting

Before adjusting

Clean air filter, fresh fuel, correct spark, no intake leaks and free throttle linkage

1. IdentifyConfirm engine + carburetor family

2. Clean and inspectJets, bowl, needle, choke, intake boot

3. Set baselineIdle / pilot / float only from the right manual

4. RecheckWarm idle, takeoff, load response and hot restart

How to adjust the Yamaha G1 carburetor

Confirm this Yamaha G1 matches the carbureted setup shown above. If the vehicle has EFI or no carburetor, do not use these adjustments.

Identify the engine and carburetor before turning any screw. Engine/application: Yamaha 2-stroke gasoline. Carburetor: Mikuni BV21-161.

Before adjusting anything, check fresh fuel, tank venting, fuel-filter and pump delivery, the air filter, intake boot or manifold, spark plug and choke operation. A carburetor setting will not fix a fuel restriction, intake leak or weak ignition.

Warm the engine fully and set idle using this baseline: 1200 rpm with V-belt removed; 1000 rpm with belt installed. Make sure throttle-cable tension or governor linkage is not holding the throttle plate open.

For the pilot/mixture circuit: Pilot screw baseline: 1-3/8 turns out. Only change an adjustment that the exact carburetor is designed to have, and make small changes before rechecking warm idle and throttle response.

For float and fuel level: 18 mm (0.7 in). Then verify choke release, hot restart and smooth transition from idle into governed speed without surging, hesitation or flooding.

G1 carburetor symptoms

Runs only with choke

Usually points to a lean condition: dirty pilot and main circuit, restricted fuel supply or intake leak.

Heavy smoke

On the G1, also verify the 2-stroke oiling/choke system before blaming the carburetor mixture.

Hunts or surges

Check pilot circuit, intake leaks and governor and throttle linkage before changing the idle stop.

High idle

Make sure cable tension or governor linkage is not holding the throttle plate open.

Stalls when warm

Check pilot passage, idle baseline, valve or compression condition and heat-related fuel restriction.

Bog when throttle opens

Inspect transition/main circuit and fuel delivery; an idle adjustment will not fix a blocked main jet.

G1 carburetor specifications

Applies to: Carbureted gasoline version.

Engine: Yamaha 2-stroke gasoline.

Carburetor: Mikuni BV21-161.

Idle: 1200 rpm with V-belt removed; 1000 rpm with belt installed.

Mixture: Pilot screw baseline: 1-3/8 turns out.

Float: 18 mm (0.7 in).

Choke: 1 mm (0.04 in) choke-cable free play.

Governor: Keep the factory governor and linkage setting.

Model-specific note

The G1 service manual publishes a Mikuni BV21-161 carburetor, 1-3/8-turn pilot screw baseline, 18 mm float height and 1200 rpm idle with the belt removed (1000 rpm with belt fitted).

Yamaha G1 carburetor FAQ

What is the correct Yamaha G1 carburetor idle setting?

1200 rpm with V-belt removed; 1000 rpm with belt installed. This is the model-specific baseline shown for the applicable carbureted version.

What is the Yamaha G1 mixture-screw setting?

Pilot screw baseline: 1-3/8 turns out.

What is the Yamaha G1 carburetor float setting?

18 mm (0.7 in).

Why does my Yamaha G1 only run with the choke on?

That usually means the engine is running lean because of a restricted pilot and main passage, weak fuel delivery or an intake leak. Clean and diagnose the carburetor before simply richening the mixture.

Can the governor make a Yamaha G1 look like the carburetor is out of adjustment?

Yes. Incorrect cable or governor linkage can hold the throttle open, cause hunting or limit throttle travel. Confirm linkage movement before changing carburetor settings.

What should I check before rebuilding the Yamaha G1 carburetor?

Check fuel quality, tank vent, filter and pump delivery, air filter, intake leaks, choke operation, spark plug, valve or compression condition where applicable and throttle and governor linkage.

Match the carburetor to the exact vehicle

Idle RPM, pilot screw baseline, float height, jetting and governor and linkage settings can change by engine, carburetor and model year. This page applies to the carbureted gasoline version. Verify the engine and carburetor ID before changing settings, and use the factory service manual for any value not explicitly listed here. For manufacturer documentation, visit the official manufacturer website.