Motorbike surging

[Bernard]

Hi guys need help, trying to get my 2009 csr 125cc twin on the road, having a problem with the engine surging when i set the idle, got a brand new set of carbs on the bike which are set up as they should be, tank cleaned out, new petcock, the bike starts on the choke, then it just wont idle, ive checked throttle cables going to carb which are fine, the bike will rev fine but will not idle, im at a loss, could it be air filter

[Jackgardner]

Hi guys need help, trying to get my 2009 csr 125cc twin on the road, having a problem with the engine surging when i set the idle, got a brand new set of carbs on the bike which are set up as they should be, tank cleaned out, new petcock, the bike starts on the choke, then it just wont idle, ive checked throttle cables going to carb which are fine, the bike will rev fine but will not idle, im at a loss, could it be air filter

Hello,

From your description, it seems like you've already done some troubleshooting and maintenance on your 2009 CSR 125cc twin motorbike. Since you've checked the throttle cables, cleaned the tank, installed new carbs, and have a new petcock, let's explore some other potential causes for the surging and idle issue:

Air Filter: You mentioned it as a possibility, and indeed, a dirty or clogged air filter can disrupt the air-to-fuel ratio and lead to engine problems. Make sure your air filter is clean and not obstructed. If it's been a while since you replaced it, consider getting a new one.

Vacuum Leaks: Check for any potential vacuum leaks in the intake system. Loose or damaged hoses, fittings, or intake manifold gaskets can introduce extra air into the engine, causing erratic idle and surging.

Idle Adjustment Screw: Ensure that the idle adjustment screw on the carburetor is set correctly. If it's not adjusted properly, it can affect the bike's ability to maintain a stable idle.

Idle Jet Blockage: Even with new carburetors, there's a possibility of small particles or debris blocking the idle jet. Try cleaning the idle jet thoroughly to ensure proper fuel flow during idle.

Ignition System: A faulty spark plug or ignition coil could cause the engine to misfire at idle. Consider inspecting the spark plug, ignition coil, and associated wiring to make sure everything is in good condition.

Fuel Delivery: Double-check that the fuel flow from the tank to the carburetor is steady and uninterrupted. Any fuel supply issues could lead to the surging problem.

Throttle Position Sensor (TPS): Some bikes have a TPS that can affect the idle when it's not functioning correctly. Verify that the TPS is working as expected.

Exhaust System: An exhaust leak could impact the engine's performance. Check the exhaust pipes and connections for any leaks or damage.

Carburetor Synchronization: Ensure that the new carbs are synchronized correctly. Improper synchronization can lead to an unstable idle.

Since you've already checked and ruled out some potential causes, it might be worth focusing on the ones you haven't inspected thoroughly yet. If you're not confident in diagnosing the issue yourself, it's a good idea to take the motorbike to a qualified mechanic or motorcycle specialist who can perform a comprehensive diagnosis and find the exact problem.