Topic: Clunky idle

[mgilvary]

I just installed a Dyna S ignition, coils and wires on my 75 CB550, and that all seems to be working great, but it didn't get rid of a problem I was hoping would go away, which is a clunky idle. I need to keep the idle at around 1800-2000 RPM, or the engine chugs and clatters a little bit. It won't usually stall, but it keeps a very inconstant speed.

For example, I dynamically timed the new ignition, but it was hard keeping the bike idling at a clean 1000RPM.

I suspect that I'm going to have to learn a lot more about carbs in order to fix this problem (my plugs seem to come out sooty no matter where I set the adjusting screws). But, before I get into pulling the carbs, cleaning, re-jetting, etc., I wanted to see if anyone thinks this might be a cam chain issue.

My cam chain adjuster seems to be bound up. I can't turn it either direction. If it was just a rough idle, I wouldn't worry about it. But the clunking below 1500 RPM worries me. This is my first bike, so I'm not familiar with what is a normal sound from these engines. Any thoughts?

[CB500_k2]

I just resolved the same problem on my CB 500 by balancing the carbs.  The clunking at idle is not uncommon.  Typically, the noise comes from the clutch.  An uneven idle will cause the clutch basket to rattle.  The most common solution is to dynamically balance your carbs.  This is done with gauges or manometers connected to each carb inlet.  There are screws to remove to mount the gauges.  Get a Clymer manual for details.

[n9viw]

Ditto on the synchronizing the carbs. Mine had the same problem, it was quite noisy at lights, but even a bench-synch took care of most of it, and a dynamic synch with the merc tubes will do the rest.
The cam chain tensioner will adjust properly when the engine has some tension on the chain. It helps to preload it by holding down the kicker, just enough to put a little pressure on the drive but not enough to turn it over, then loosen the locknut on the adjuster, then hold the adjuster with a screwdriver while you tighten the locknut. Sounds complicated, but it's relatively easy once you've done it, especially if the carbs are off for cleaning.

[MetalHead550]

3rd vote for sycronizing your carbs.  Not real hard, any good service manual will describe the process.  I would recommend getting a murcury type manometer and not the gauge type.  The murcury are much more accurate and dont fluctuate like the gauges.  Probably around 50 bucks for a decent manometer.  Also make sure your timing and fuel mixtures are good before syncing.  In my experience running really rich due to improper pilot screw adjustment or floats set too high can cause symptoms simular to yours.  Run the bike till its good and warm then pull your plugs to check for overly rich mixture.  Theyll be black and sooty and reek of gas.

[SteveD CB500F]

Agree.

Get some Morgan Carbtune balancers.  They look like mercury tubes but don't use any of that nasty stuff - they use steel plungers!  I bought mine on eBay for about £20.

[mgilvary]

Looks like I'll be synching carbs on some weekend in the not-to-distant future. Thanks, everyone.

M.