Throttle down - sounds like a blow off valve!

YYZRC · June 2021

Any idea why my 6.2 has a hiss noise when throttling back (no load)?

https://youtube.com/shorts/U67Zm0T-puo?feature=share

PickleRick · June 2021

Usually a hissing noise is associate with a vaccum leak.

Hopefully a vaccum hose has popped off. At idle someoene who vapes can find it pretty easily if they can blow smoke over the top sides of the motor

YYZRC · June 2021

No vapers here. Would a vacuum leak make the sound you hear in the video - only when throttling down?

PickleRick · June 2021

My cell phone has crappy audio so I cant make it out 100% but your description of a hiss is the noise an air leak would make (naturally aspirated engines make the most vaccum at idle)

I bet you'll find a little hose that has popped off.

Aqua_Aura · June 2021

It does sound like vacuum. It seems like the sound is still there at idle as well. Haven't messed with a carbureted engine in a long time but I believe when the throttle is closed it creates more vacuum and that's why you hear it louder on throttling down.

Willhound · June 2021

Yep, take the spark arrestor off ( watch that little nut or washer doesn't go down the throttle body) and check for a smaller hose that just pushed on to a nipple near the base of the throttle body/carb. Makes that exact noise.

YYZRC · June 2021

I don't see where a hose connects as per the parts diagram?

Image: https://us.v-cdn.net/5020499/uploads/editor/e8/x0vmwvl939kc.png

davidbrooks · June 2021

Not sure about the carborated models but on the EFI ones if you have a vacuum hose disconnected you will also notice a difference at idle. It happened to me once and i thought i had a bad MAP sensor. Turned out to just be a disconnected hose.