Backfiring after valve adjustment

[jeeves]

Adjusted my valves a few days ago.
The scooter runs a lot better now (last valve check was a looong time ago), but now it's backfiring when decelerating, and the fuel consumption has gone up (didn't do any carburetor adjustments).

Actually did it twice.
First time both valves were adjusted to 0.10mm (0.04). Then it started to backfire, so I thought they were too tight. Did it again this time 0.12mm (found this value in service manual for Agility city 125), but almost the same, just a bit less backfiring, but the fuel consumption is still higher then before.


Don't think I have a leak in the exhaust, because when I cover the exhaust the engine dies.


Any ideas people?



 

[jeeves]

OK, found the problem!

It had nothing to do with the valve adjustment.
Just before I did the adjustment I also unplugged the automatic electric choke to test it, because the idle speed was somewhat erratic. After the check I still wasn't convinced it was ok, so order a new one from http://www.ebay.com/itm/331012363633?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649 (5.28$ cheap!!!), and,of course, I forgot to plug it back in!   
So I had been riding without it for a few weeks. 
The scoot would start up and run fine, probably due to the temperatures here being around 30°c (86°F), but it would backfire at deceleration, and when hot, needed a bit of throttle to fire up. Also had to adjust the idle screw.

The fuel consumption went up considerably, but I still didn't understand why.

Soooo, finally the automatic choke came, and when I went to change it I saw the cable unplugged

Put in the new choke, and the scoot is now running fine, no more backfiring, starts up every time, and the fuel consumption is even a bit lower then it use to be. Had to adjust the idle screw again.