Weird motor noise

[Navrothian]

Hi everyone, just a quick question as I need to be pointed in the right direction on this one. Still a very novice user, but getting better every day.

After I fixed the sheered woodruff key, the bike ran great for a few days. Now at about 3/4 throttle, the engine noise changes.

I go from a nice consistant rev, and then I level off at about 40km/hr. When I hold the throttle there, the reving changes back and forth from a nice rev to a jackhammer sound, then back again.

The jackhammer sound is quite nice. It sounds like there is more power being generated at that time, but it is much louder than the normal rev.

I hope I have explained this ok, any direction would be appreciated.

Thanks,

Nav

 

[crassius]

does it sound like popcorn popping or like an angry bumblebee?

 

[Navrothian]

Neither really.

Best i can describe is like the sound of a jackhammer going full tilt.

I used the choke just a min ago for the first time. Never need it because bike starts first pop every shot.

It didnt make the noise this time and i was able to cruise at 50 km/hr hmmmmmm

 

[crassius]

sound could be detonation from being so lean that it is overheating

first, check that motor is tight because shaking the carb can make it go too lean

if motor is tight, then air leak can make it too lean also

 

[Navrothian]

Motor is very tight, I cannot move it one bit as I hold the bike and push on it with all I got.

Every other day I make sure every bolt and screw on the bike are secure.

I like the sound I wish it would sound like that all the time.

Where would I check for air leaks?

Thanks for all your help

 

[Navrothian]

And what is it exactly when you say it's too lean? Is the fuel/air mixture messed up?

Ok I figured out the meaning of lean --- too much air

 

[Frankenstein]

No no no, it's rich, but only slightly. No way he has an air leak making it lean and has no problem starting without a choke.

That which you are experiencing is 4 stroking. If you just start to choke the bike at slightly lower speeds it will do exactly the same thing. It will also stop doing it up hills with more load behind the motor.

Whatever jet you have in there should be swapped for the next size smaller and you'll probably gain some top speed since it seems your bike is in its sweet spot.

He's only hitting 31mph before it does it, and he's on a newer motor so as it breaks in its going to richen up a bit as it all seals up tight. If the weather changed dramatically enough where he is and got warmer then that will also start the 4 stroking suddenly.

 

[Navrothian]

I will look into this, thank you

 

[Navrothian]

Looks like my pin in the carburetor is bent slightly

Thanks for the heads up

 

[Navrothian]

I have a nt speed carb, pin is bent, and doesn't look like it's adjustable like others I have seen