Idle issues....

[Islandstar]

Hope this is the correct section...first on my cb 400 it idles fine but if I give it throttle it sticks at about 2000rpms before it come back to regular idle. Where should I be looking? Got it back from mechanic a few weeks ago after having carbs cleaned/serviced. Thanks

 

[teazer]

Start with the easy stuff. Check the throttle itself for stickiness and then the cables and linkage on the carbs. It may be a simple mechanical problem like sticky parts so eliminate that first.

Then mechanically synch(ronise) the bank of carbs. What that means is make sure that all four slides start to rise at EXACTLY the same time and they all disappear at 3/4 or so throttle at the same time.

And while you are there, check that all the hose clamp screws are done up tight. Not so tight that it causes you to burst a blood vessel. But not loose.

If that's all 110% AOK then we move on to potential air leaks. High idle is often a symptom of a lean mixture caused by an air leak. So we want to look at the filter connectors and where the carbs attach to the head. A simple test is to run the bike and carefully spray WD40 around the connectors and see if idle speed rises or falls as the motor sucks in the WD40.

After that it suggests either carb jets still not clean or ignition. Most bikes of that era have a mechanical advance/retard and with age that sometimes gets a little rusty. Remove the points cover and clean and check the points and lube the A/R unit.

 

[Islandstar]

Thanks