S3 99, Surging, backfiring

Wondering if any members can help?

I have a 99 S3 with 80,000km's on the clock, but recently it has started popping and wheezing in all conditions, also stalls. Strange thing is it still goes well, revving freely to the limiter, but you can feel it surging when cruising and popping when decelerating, it then sometimes “chirps” and stalls at idle. When is does idle in regularly “chirps” and looses rev’s, like a cylinder is dropping.

I have tried additives for both injection cleaning and decoking. I always run her on 98 octane premium unleaded. When I give it a real handful I can see “brown” smoke out of the exhaust.

Having said all that I love the bike.

[Calitriple]

I have almost the exact same bike as you, a 99 S3 with 34k miles ('bout 75km) on the clock. I get a bit of backfiring when I let off on the throttle.
Does yours sound like it's sucking a little wind? If it is it may be an exhaust leak.
My old cr250 did the surge and die thing once too. Found out my step brother had done me the glorious favor of washing out the gas tank. Next time I put gas in it there was water in the tank, wreaked havoc with it. Did almost exactly what yours is doing. On my CR I just drained the tank and lines and added some fuel injector cleaner (supposed to get rid of water) even though the bike was carbuerated. Might wanna research that first, though. Check with cheapbastard, he'd know. Look in any of the other threads and you'll find him. At the bottom of one of his comment there's a tab where you can send him a private message.
Good luck and welcome to the asylum... ">

[ This message was edited by: Calitriple on 2006-07-14 03:30 ]

Calitriple, thanks for the reply; mine does sound like it's sucking/blowing air, sounds like a compressor. One place I had look at it said it was due to carbon buildup in the cylinders, but I ride her pretty hard and don't think this would be the problem, but have used a decoking additive anyway, which didn't make any difference.

[dml955i]

Check to see if the sparkplug on the sidestand side of the bike is corroded and fouled. Water tends to collect there (common problem)

Also may need to have your throttle bodies calibrated & re-synched.

Thanks dml955i, I'll check those things as well, really appreciate the responses.

[amberale]

Beemer, if that 98 octane is Optimax then you could have carbonned up you plugs and head.

I had an awful time with it in my old monster every time I got stuck in traffic while commuting. It's ok for racing or out in the mountains but seems to be too dense for bikes at low revs/throttle.

AA

Amberale, I have used a fair amount of Optimax, so you could be right. Thing is what to do about it?

[amberale]

On my old bike the main problem was fouled plugs.
I'd start by putting new plugs in and see if that fixes the problem.

I have heard stories [unsubstantiated] of guys needing top end rebuilds due to carbon build up, but I wouldn't panic about that yet.

My monster would drop one cylander and runlike a dog or not start.
Fortunately the plug were easy to change. I used to carry a couple of spares.

Change the plugs, fill the tank with Ultimate and take her for a good long ride somewhere where you can open it up.

Might not work this weekend if this rain actually comes.

Good luck AA

[amberale]

Just had another thought, if the fuel was already too dense to burn clean then additives might have added to the problem.