Backfire on the over-run

[nickst4]

My Skorpion Tour has a tendency to frighten horses and old ladies when I shut the throttle, sometimes after quite small throttle openings. Looking at the notes in the handbook, the first owner noticed this and took it back to the supplier, and believed it was fixed by leaning the mixture a tad (presumably the tickover mix; the opposite of what I might have done). But then he commented it had come back again.

Is this common? Might it imply bad valve adjustment (since new)? Any ideas gratefully received, so I can avoid having the silencer rupture!

NickW, UK

[handsomejackuk]

sounds cool to me..

I love frightening the opera goers, and my next doors parrot


hehehehehhe

Jak

[Berniecal]

In my experience, this is caused by a lean mixture and/or an air leak into the exhaust, either at the head, or at the pipe to silencer joint. Try raising the tick-over a bit, richening the idle mixture, and check all joints. I have a 2002 Tour that burbles and farts on the overrun, but every big single I've owned has had this feature to a greater or lesser extent. Quite a head-turner!
We're surrounded by open-pipe Hardley-Ablesons over here, so the old ladies and horses have got used to it!
Bernie in Calgary

[Linegeist]

Hi Nick,

Mine did this when I first got it (sounded like the bloody Somme and one particular horse rider threatened to introduce my bike to my nether regions ) and the cure was to simply seal the silencer to downpipe joint near the r/h foot peg. Immediate fix, and the thing now burbles sexily on the overrun sans bangs.

Silicone bathroom sealant is rather good as it stays flexible, but bakes on the joint to seal the gaps. It's easy to remove as well.

[Bill Jurgenson]

join the club. If it didn't something would be wrong.

Don't worry about it an don't waste time trying to fix it. it can't be fixed really. The carb has a small membrane (top left side of left half) which is supposed to richen slightly for this reason. Supposed to...

[MSW]

...the cure was to simply seal the silencer to downpipe joint near the r/h foot peg. Immediate fix, and the thing now burbles sexily on the overrun sans bangs.

Same thing with mine, and sealing a leak in the exhaust did wonders for me as well. As Bill said, it never really goes away, but the loud pops might well be due to a leak either there at the connector tube or right at the head (e.g., if you've R & R'd the headers a few times without replacing the copper gaskets).

[rodge70]

@linegeist,good idea with the sealant, as mine had started to pop more than normal and black marks all round the joint i pulled it apart today and the gasket fell off in about 3 bits .found a length of glass rope for sealing gas flues etc,siliconed that to link pipe and then bolted silencer on,all seems good so far.
another tip, when checking battery level and you find the rubber band falls of the lower hook,fix a cable tie on band,fit band to hook then slide cable tie down toward the lower hook and pull it to secure to band,hopefuly next time the band will stay fixed to lower peg

[nickst4]

Hi Nick,

Silicone bathroom sealant is rather good as it stays flexible, but bakes on the joint to seal the gaps. It's easy to remove as well.

Thanks for the tips, and reminding me of the uses for silicone rubber! You can get high-temperature versions used for boiler flues, good for 300C, and the type I've got is a natty red! So I packed that rather loose joint at the foot-peg and, hey presto, it STILL backfires, but maybe a little less. So I need to look at the flanges at the head too. I've not tried tightening them yet, but I lifted the silencer and slid it further on to improve clearance and The Look, so there might be a slight leak there. Almost time to bring the bike in out of the cold and salt and start on a regime of carb/pump/tank work, prompted by the collective wisdom here and on the Yahoo group.
All good fun!
NickW, Norfolk, UK