Sounds like a rattle or knock or ping. By marvinlee (Read 3,860 times)

[marvinlee]

I have a 2008 lance duke 250cc. Recently I hear a knock, ping sound right when I give it the gas after coming to a stop. As soon as I take off the ping makes it rattle then goes away. It's not the cluch vibration or anything, just a rattle ping sound for a second when torque is being applied caused by acceleration. Do you guys think it could be crappy fuel and not enough octane? Everything else is good. Help? The only recent thing I have done was get some cheap octane boost and went to different gas stations . My motor is the Honda cf Moto clone , which I'm pretty sure has a compression ratio of 10:1. My gut says get chevron premium, and a bottle of techron. If it were the valves, it would do this all the time right? It's got pretty low miles, 890 when I bought it now about 2000

[Bashan]

My CF Moto Fashion does exactly the same thing. I first noticed it about a 1,000 miles ago. Like you, I thought it might be the gas but no matter what I burn it still does it. I had the CVT cover off a while ago and checked everything to no avail. I set the valves and it made it run better but still the noise is there. It runs perfect and isn't getting any worse so I quit thinking about it. In a couple thousand miles I'm going to tear it down for a project and see if I can find something. Let me know if you discover anything. Rich

[marvinlee]

Thanks for the input. I noticed its prone after long rides, I go up the basin here in Idaho; from 2400elv, to 5000elv. It seems it tends to do this after the decent coming to a stop, then taking off like you said as well. Well who knows, I just ease the throttle at first then I'm good to go. I'll see what Chevron gas does and try that. Thanks

[Cruiser]

It sounds like you guys are getting a "spark knock" or pre-ignition. No big deal as long as it doesn't happen while cruising down the road. It can hole a piston under these conditions.

Early model cars (carbs and point style ignition systems) overcame this with a vacuum advance unit attached to the distributor. When accelerating like from a dead stop, the vacuum drops which would momentarily retard the ignition timing. As the engine would gain speed and vacuum would rise, the timing would slowly advance to normal. Modern engines use the ECU to control this. Most Chinese scoots are sort of in-between these two technologies. They have no way of compensating for initial spark knock unless they have fuel injection or a more sophisticated ignition system than just a simple CDI.

[justbuggin]

i was thinking the rollers could be making the noise due to flat spots just an idea

[marvinlee]

Well here is another thought. Do these CF moto engines have a chain tensioner of some sort? It's as if when torque is applied at take off, we hear a tink, rattle rattle. Then goes away. Sounds like the timing chain, if it has one, needs just to be a tad tighter. What do we think?

[Bashan]

It has a spring loaded tensioner just like a GY6, no adjustment necessary:

[marvinlee]

Well that's a relief; one less thing to repair.

[nulldevice]

Cam chain tensioner is automatic.

Check out the callipers. Grab them and try to shake them in all directions. If one or both rattle you've found it. The rubber calliper mounting bushings are worn out or missing.

[nulldevice]

After many days I have found the noise sources. Note the plural.

1. Loose carburetor mount hose clamp caused the sucking whistling noise and the carb bowl knocking on the motor mount.

2. Idle slightly too high and making the clutch bell wiggle back and forth at idle.

3. Contaminated and glazed clutch shoes caused chatter at take-off

4. Destroyed rear caliper mounting bushings caused a horrendous high pitch rattle at all speeds

5. The guts of the muffler were loose and rattling around inside.

These scoots are such fun. It has been too hot to ride much lately and it kept me out of trouble and entertained in my basement.

[marvinlee]

I had # 2 . I lowered the idle and it helped dramatically, even after a long ride or standing in traffic waiting for the light to change. crap I hear a raccoon coming.