weird suction sound when i kill motor

[rawdog12571]

i ahve been working the bugs out of my bike for months now but still when i shut off the bike when hot it makes a weird suction noise idk wtf it is...i had many problems with it thinking major stuff but it was mainly vacuum leaks and i got my power back but it still backfires on deceleration but this noise is really weird im just wondering if anyone knows...thanks

 

[Rogue21]

Have you checked the carbs? When you said suction noise, the first thing that came to mind were the carb slides/diaphragms, but I'm not sure how it would be correlated to shutting the bike off.....?

 

[WacoBrian]

does it have a pamco?
sorry i misread the post, i was still asleep

 

[RFLIVES]

Have you installed pods and a brake check valve? if so it's most likely just the brake check valve.

 

[blackbetty]

^

Yup, mine does it too. Kind of a low moan. It'll also do it if you turn the kick starter very slowly with the bike off.

 

[TeeCat]

It may have something to do with the breather apparatus as the pistons move the last bit of air while coming to rest. It's even more accentuated with a reed valve.

TC

 

[rawdog12571]

no pamco....it is an 81 by the way yes with pod filters and open exhaust also my friend did the hieden carb kit and new diaphrams for me..i was thinking it could be a valve too but idk...im gonna have another friend look at my carbs and he has a manometer which im not familiar with.....but what is this brake check valve? im gonna do some research now...thanks guys

 

[cobrasneverdie]

just wanted to revamp this thread cause now I am hearing it on my bike and i want to know if anyone out there can answer this

 

[TwoManyXS1Bs]

Only 2 things come to mind:

- Ignition post-fire, sometimes happened on ratty 'ol 4-cylinder bikes which had the 1-coil/2-plug ignition, mild backfire thru carb of non-compressing cylinder. The operative term here is "ratty 'ol".

- Leaky rings. A test for this is to sloooowwwlllyyy kick-thru the engine, listening for that sound...

 

[XSLeo]

On electronic ignition bikes, when you turn off the ignition it fires one more time. this is often heard as a woosh sound.
With stock air boxes you won't hear it, but with pods you will.
speaking of pods, what kind do you run? The pleated element filters like the K&N and similar knock offs could be part of the running issues. The shorter and more tapered the worse the effect.
A long straight foam filter fixes a lot of carb tuning issues.
Leo

 

[cobrasneverdie]

I'm running uni filters on mine, I also do have the electronic ignition. But it started happening after I ran it on the highway.