I changed the oil today and after driving for a while it started to make this funky humming noise. Its much louder when I take the lid off of the air filter. I kinda freaked me out since I tried a new oil. So I drained it and put my old kind back in but the noise continues. You really only hear it much when its idling. Any and all advice would be appreciated, short of a new engine.

 

Sound like its the shutter valve that part is right under the carb....

Later
Dan Atkins

 

Dan's correct, sounds like a cross between buzzing and honking noise. rx7doctor

 

It has been idling like crap and it was doing a little bit of backfiring. Guess I know what Im doing tomorrow.

 

I put a new shutter valve vacuum unit on my emissions, when I rebuilt my carb. I can still get a slight "honk" when I reduce the idle to around 500 rpms while playing with the throttle return spring / throttle cable adjustment (I was seeing how low I could get it to idle after fixing a vacuum leak). I still get a slight backfire on occassion, too.
Shutter valves are boogers!
How'd did your shutter valve repair go?

 

just remove it