Backfiring 4T

[misterbrackets]

So, I'm not too concerned about this since it really only happens letting off the throttle going downhill, and there aren't too many hills where I live.

But.... I'd like to know what it means since in might be indicating something off with the fuel mixture or the timing.

In addition to timing, I've heard that it can be a lean OR rich mixture with the idle circuit.

So, what's the most likely scenario?

Thanks!

[Robbie]

The term is 'Afterfire'....a backfire is on the intake side.

Anyways, the most common cause of afterfire is a loose or leaking exaust system.
The system pulls air into itself in between exaust pulses and lights the unburned fuel that is thrown into the exaust when the engine is at speed but the throttle is closed.

In the case of the Stella, I'd be looking closely for a exaust pipe developing a crack, a known issue on the 4t's.

Rob

[listless]

Exactly -- crack in the exhaust.

I've been through two of them in as many years.

One replaced under warranty and I get it welded back together last time.

Should be an excuse to get that Sito plus if I could find one for sale for the 4T...

[ericalm]

First place to look for a crack is the heat collar under the header. Ugh.

Should be an excuse to get that Sito plus if I could find one for sale for the 4T...

Like this one? http://www.scooterworks.com/sito-plus-e ... n240JF2STU

Er, out of stock?!? Bah. Their "email when in stock" feature does work. I'd try calling them too. The site may not be current.

I'll be getting one soon.

[viney266]

yeah, that pipe is so cheap its a no brainer. Get a one size larger main jet while you are at it. a little tweak of the air mixture screw and she runs better.

I put one on a friends 4T a few weeks back, not a huge improvement, but a little better, and if it doesn't crack its worth every penny.

[ericalm]

Well… crud. Sito has gone bankrupt. They stopped shipping last month. The Leo Vince brand will live on in the US, but probably not the Sitos. So. Blah!