Odd sound

[Canon]

I finished my third build last night and put a few miles on it today. I noticed an odd sound coming from the engine. It sounds like a piece of metal is vibrating against the frame or tank, but there is no such vibrating metal as far as I can tell. I don't know if its benign or something horrible because my engine seems to be running fine. The only other time I have heard this sound was when one of my head bolts was stripped on a previous build, but this was much louder and the bikes performance suffered greatly so I do not know what to do.

 

[Canon]

Id like to add that it makes this noise constantly, whether its idling or revving.

 

[AussieSteve]

First, ensure that there's definitely nothing external causing the noise. ie muffler banging on frame etc

Can you tell which part of the engine casing the sound is coming from?

A good method of tracking down engine noises is to grab a screwdriver firmly by the handle, with your hand extending just over the top of the handle. Next, place the pointy end of the screwdriver firmly on the section of engine that you wish to listen to, then place your ear against the hand holding the screwdriver.
The sound will be clearly transmitted through the screwdriver.

NEVER DO THIS AROUND MOVING PARTS. You don't want the screwdriver driven into your ear, handle first. Might hurt.

Not a bad idea to remove all side-covers for a look. Ensure that all nuts are tight and that everything seems OK.

(The sound that you describe sounds a little like it could be a bad small-end bearing or similar.)

 

[will_start]

I wanna know the answer...I hate riddles.

 

[motorpsycho]

I would check the muffler myself. it could have something loose in the inside where you can't see it. the cateletic peice is only held in by one screw (in some cases) and if the scew comes out, that peice will vibrate inside the muffler like crazy. even a stray screw that could have found it's way into the muffler during assembly or packaging will make a vibrating noise loud enough for you to hear it.
does the vibrating noise change speed with the engine rpm's or does it stay the same no matter what the rpm's are?
I would pick the bike up off the ground a few inches and drop it on it's wheels (without the motor running of corse) to rule out any loose parts banging or rubbing on the frame that do not have anything to do with the engine running.

 

[Canon]

I'll try the screwdriver thing after work, and I checked the bikes external parts thoroughly before posting. The noise isn't nearly as prominent anymore but its still there. And the only performance issue I've noticed is the first 45 seconds of running I have to have the choke on for awhile and slowly increase the throttle or else it bogs down really easily. This might have nothing to do with the sound but its something I've never experienced with one of these engines before.

 

[biketec]

What motor is it?

 

[AussieSteve]

Canon, the choke thing sounds like you might be sucking air where the carb joins the inlet, or where the inlet joins the barrel.

biketec, I think it's a 66cc Skyhawk. Canon will enlighten us.

 

[Canon]

yes its a 66cc skyhawk. I turn the choke off after a few seconds and it runs fine.

 

[biketec]

Not to be a nay Sayer but, I'm going to say its the bottom end. I have had quite a few come back recently with that I have built and heard a metallic ting ting to them. I hand them over next thing I know I am getting the bike back.