How to Troubleshoot a Mikuni

When a Mikuni carburetor malfunctions, the amount of air flowing into the engine can be interrupted, causing damage to both the engine and the carburetor. Vibrations caused by normal use can loosen plates and cables, while long periods of non-use can cause clogged jets. Troubleshooting a Mikuni carburetor can be done with a few tools and may require an extra pair of hands.

Instructions

1




Allen wrenches come in several sizes.

Remove the air cleaner cover with an Allen wrench. Loosen the air cleaner with a Torx wrench. Disconnect the breather tubes and remove the air cleaner. Remove the backing plate with a socket wrench.

2

Put the engine in neutral, then start it. Wait until the engine is hot to proceed, but do not turn it off.

3

Spray the jet with carburetor cleaner. The engine will stumble, then recover. Repeat this process once.

4




A flathead screwdriver is also called a slotted screwdriver.

Adjust the idle speed screw with a flathead screwdriver until the engine idles smoothly.

5

Rotate the low speed fuel-air mixture screw 1/8 clockwise. Wait for the idle to stabilize, then repeat the process until the engine stumbles. Once the engine stumbles, rotate the screw 1/8 counterclockwise.

6

Shut off the engine and reinstall the backing plate, air cleaner, breather tubes and cover.

7




Pointed channel lock pliers work better to reach screws.

Use either your fingers or pliers to adjust the throttle cables. If the engine is cold and difficult to start, the throttle plate may not be closing properly. Tighten the cables until the throttle plate remains closed when idling.

8

Use a flathead screwdriver to tighten the idle mixture screw on the side of the carburetor block if the engine has been running for a while and is difficult to start.

9

Inspect the air intake hose for any damage or cracks. If present, replace the hose. If not, clear any visible blockages inside the hose.

10

Inspect the enricher valve. Turn on the engine. If it visibly rattles, it is not seated properly. Shut off the engine and readjust the valve with a socket wrench. If the enricher valve is wet to the touch, there is a leak and the valve needs to be replaced.