Whoosh noise then engine cuts out.

Can anyone help, after a long run when I pull up or come to a junction, pull the clutch in I hear a whoosh noise like a sudden release of air then the engine cuts out, smoke comes from under the tank near the handle bars. The engine will restart and I'm on my way again. Any help is appreciated.

 

Thanks for the welcome. It's a 2003 vfr800 with 31000 on the clock. The smoke only lasts a couple of second and is gone

 

I suppose it's when at idle.

 

I don't think it has a EVAP cannister

 

How does the bike run overall? Is it hard to start?

This sounds a bit like a problem with back-pressure in the exhaust, like there's a blockage or obstruction somewhere in the exhaust.

If there's a partial blockage of the exhaust pipes the bike would be prone to stall at idle as the owner has described and the "puff of smoke" after the stall would be the built up exhaust gasses exiting through whichever intake valve(s) are open. The hiss is this pressure forcing its way out through a partially open intake valve and into the air box.

That's my guess/theory based on the information given by the owner.

 

It runs well and always starts first time. When I get time I'll remove the tank and see if I can see anything obvious.

 

Smoke after cutting out from front could be bike backfiring through throttle bodies.
Check your plugs, and make sure they are the right heat type.
Have the valve clearances ever been checked? Not really enough kilometers on it for it to be needed. If you're talking miles, them it might be needed.

 

It's at the right mileage for a valve clearance check but I've heard on these forums of bikes doing 100,000 without needing adjusting. When I've got some free time I'll do some checks under the tank etc. See if I can find any clues to what it is and post them here.

 

So I've lifted the tank and noticed the air filter housing vents are in the vicinity of where the whoosh noise and smoke came from, I'm no mechanic so forgive me if I am way of the mark but their is a vacuum chamber associated with air filter housing, could this be at fault and causing the whoosh noise?

 

If you're referring to the small vacuum reservoir attached to the filter housing, I doubt it very much.
If there's smoke, it can only be a backfire I would think.
Have you pulled up the filter to look inside?

 

I'll lift the filter tomorrow to have a look.

 

Really?

The owner-described version of this problem talks about a "whoosh" noise right after engine cutout. How can this not be an exhaust back-pressure issue? Where else could the engine possibly store up a big enough volume of gas pressure to produce a "whoosh" sound backward through the intake tract, and with enough force to puff exhaust smoke all the way up through the airbox to exit through the intake snorkel off the front of the airbox (just behind the steering tube)?

 

Hi Gregindenver, i'm a complete novice with mechanics but willing to explore and have a go, can you suggest a solution, do I need new exhaust or is there something I can do to fix it. The exhaust is old and rusting.

 

That's a thought, check that the bike wasn't stored and some critter hasn't built a nest in your muffler.
It has to be gases coming back through TBs.
that's why I mentioned checking plugs.
Too hot a plug range or excessive build up could be preignitioning the gas/air mixture before intake valves close at idle.

 

I agree with you actually, but holy moly, you need to mellow out and take a chill pill hombre! You seem very high strung. Well, maybe you're having a bad day I guess....I do hope it gets better if so!

That said, I think that what gregindenver stated makes the most sense based on the circumstances. Whatever it is, I would not go on anymore rides until you figure it out. We had a guy or two on here years ago who parked their bike and it went up in flames....not that that would happen in your scenario....just saying, be safe.

 

yes, I'm wondering if it isn't something like the leftovers of animal activity or maybe at some point in the bike's history a small child (toddler) putting something into the exhaust, or worse, it being a case of malicious mischief done by bored teens, etc.

if it's something that can roll around (or otherwise move from one place to another inside the exhaust system) it could be that the blockage would be transient (on and off, depending on the dynamics of the gas flow through the exhaust system).

it wouldn't be too hard to investigate, starting by taking off the muffler which is a quick-n-easy 5 minutes job. then shining a flashlight through the muffler itself and then down into the header-collector portion of the exhaust. then maybe using something long and flexible to root around a bit to see if you can feel/hear any objects moving inside the collector portion.

of course, taking the entire exhaust system off the bike is a pretty time and effort consuming project. I would hope it didn't come to that.

 

and your thinking here makes me think this: one of the odd characteristics of the VFR800 throttlebody assembly is that the throttle plates close completely when you release the throttle. at idle the air flow that sustains the engine comes exclusively through the "Starter Valves". so any back-pressure released when the engine suddenly quits while at idle will have to be vented through the starter valves. that may account for more "whoosh" noise than would be made by the same amount of back-pressure exiting through normal throttle plates.

 

one final thought that occurred to me is that we know the bike is a 5th generation, but we don't know if it is a '98-'99 bike or a '00-'01 bike. if it's a '00-'01 bike it will have a catalytic converter and those things can occasionally cause problems. I have experience with cars that have had issues with their catalytic converters.