Backfiring noise?

[rainman]

A few weeks ago I took the missus for a trip up the road towards Stillwater on the GN (managed better than I thought she would ) and while we were slowing down in approach to a corner I heard a loud pop noise. I pulled over after a bit and had a look at the bike, but no burst tyres (probably woulda noticed that) or any other obvious problems, so I assumed I'd just run over a stone that I hadn't seen, or a plastic bottle cap or something. (Given it's a quasi-rural road, the stone theory sounded plausible). Took it easy for a bit, but there were no further problems, so I thought nothing more of it.

Tonight, heading down a slight downhill, in 4th gear, throttle off and slowing down as I approached an intersection, same thing - like the bike had blown a big oily bubblegum bubble that had popped. I'd been watching the road surface quite closely and it was the middle of suburbia so I'm fairly sure it wasn't a stone or bottlecap or anything. Pulled over and had a look, tyres all OK, exhaust OK, no oil dripping out of anything that it shouldn't be...

Any ideas? The bike's done 4500kms, and heading to Haldanes for a service in a few weeks, so anything nasty should be picked up then, but if something's stuffed I'd like to get on to it asap. Only similarity I can see between the two cases is I was slowing down (and I suppose I may have been in about the same gear, and roughly the same speed - but that happens often enough).

[clyde.mccabe]

Hey there, I seem to remember back in the day this was something we tried to achieve, From what i remember it is unburnt fuel making its way into the exhaust, then igniting.

we used to achieve this by hitting the kill switch at high revs with the hrottle open, when the kill switch was turned back on... BANG!

It was best achieved on the old singles for some reason, so the GN is in its element there.

am sure the guys at haldanes will ease your mind on it.

[98tls]

Its maybe running a wee tad rich...............

[Mom]

A few weeks ago I took the missus for a trip up the road towards Stillwater on the GN (managed better than I thought she would ) and while we were slowing down in approach to a corner I heard a loud pop noise. I pulled over after a bit and had a look at the bike, but no burst tyres (probably woulda noticed that) or any other obvious problems, so I assumed I'd just run over a stone that I hadn't seen, or a plastic bottle cap or something. (Given it's a quasi-rural road, the stone theory sounded plausible). Took it easy for a bit, but there were no further problems, so I thought nothing more of it.

Tonight, heading down a slight downhill, in 4th gear, throttle off and slowing down as I approached an intersection, same thing - like the bike had blown a big oily bubblegum bubble that had popped. I'd been watching the road surface quite closely and it was the middle of suburbia so I'm fairly sure it wasn't a stone or bottlecap or anything. Pulled over and had a look, tyres all OK, exhaust OK, no oil dripping out of anything that it shouldn't be...

Any ideas? The bike's done 4500kms, and heading to Haldanes for a service in a few weeks, so anything nasty should be picked up then, but if something's stuffed I'd like to get on to it asap. Only similarity I can see between the two cases is I was slowing down (and I suppose I may have been in about the same gear, and roughly the same speed - but that happens often enough).

My lovely GN used to cough and splutter for a bit and then de-accelerating gave out the best backfires I have ever heard!.......the fuel mix is too rich I think you will find......

[roadracingoldfart]

Sounds like its tappet adjustment time maybe !!
If you are getting a service soon id not panic too much just yet but tell them as much imfo as you can and the way to do that is to pay attention to the way you were riding at the timeof the event, was it down hill on the gas, off the gas or as you changed gear ..... etc.
Its very helpfull for them to analize a problem if you have all the symtoms for them.
Cheers Paul.

[Mom]

Sounds like its tappet adjustment time maybe !!
If you are getting a service soon id not panic too much just yet but tell them as much imfo as you can and the way to do that is to pay attention to the way you were riding at the timeof the event, was it down hill on the gas, off the gas or as you changed gear ..... etc.
Its very helpfull for them to analize a problem if you have all the symtoms for them.
Cheers Paul.

I had my tappets adjusted and it made no difference........GN's sound amazing when they backfire, i eventually put it down to crap fuel

[Squiggles]

my gn used to make the most beautiful back firing noise..... sounded much meaner than it really was...

eventually i dropped a valve.

but that was my gn, and with 4500 on yours i would be absolutely shocked if it happened, i think my problems were more to do with me flogging the shit out of it to get her up to 110 two up... (the lack of power was killing me! as were the vibrations)

possibly check valve clearances as someone else has mentioned? whens it going in for its 5k service?

[heyjoe]

I have heard that on bigger cruisers when aftermarket pipes are put on and the catalytic converter removed there can be probs with air getting thru and igniting causing backfire in the exhausts. This all used to happen in the converter but due to it being so muffled - it was usually not heard as that was where it burnt. Whether your situation is the same with your exhaust on the GN is something I am not sure about though.

Alos check the manifold bolts where your exhaust bolts on and see if they are loose or any leaks around there. Air can also get in there if there is a tiny gap to allow it.

[Henk]

Backfiring on the overrun when engine braking is nothing new and nothing to get too stressed about. Every single I have owned has done it to one degree or another.
It posibly means you are running a bit rich but only on the pilot circuit as it tends to happen with the throttle fully closed.
If it realy worries you tell the mechanic about it when you have it serviced.

[rok-the-boat]

Maybe you have developed an air leak in the exhaust.

[rainman]

As always, great advice provided in reponse to my noob questions. Thanks all, I'll have it looked at in a few weeks when I go for my next service.

[surfer]

You might want to check for air leaks around the air filter/carberuetor (oops spellink) as well as the exhaust manifold and rest of the exhaust pipe.

My bike pops all the time when I close the throttle down, I love it.

[Eurodave]

This sort of backfiring is caused by air leak/s in the exhaust system somewhere, just pull the exhaust pipe & muffler off, install a new exhaust gasket into the head,poo a little high temp silicone or Maniseal around the header pipe to muffler joint , tighten everything up & go for a ride!

[Krayy]

My VTR had the same thing and it ended up being one of the spark plug leads that had a split in it where it attaches to the spark plug and was skipping firing. Next cycle there was unburnt gas in the pipe and "boom". Replaced leads and all happy since.