backfire?!?

GoldenMotor.com

Elixys

New Member
Sep 14, 2010
127
0
0
Midland, TX
hello everybody,

im having a couple of minor problemw with my china box.....i dont know if anyone knew or not but a couple of weeks ago i successfully replaced my the top end, (bowing to my own mechanical excellence) after a destroied intake manifold ate the inside of my origional cylinder jug out....the only problem is i had to shave 1/16" off the piston skirt to keep the new piston from hitting the crank housing and causing it to bind.....but enough of that, i got all of that taken care of. right now im having a few problems with my motor backfireing......its not a real backfire like in the old movies with one loud bang and then off she goes, it makes more of a silent pfft kind of sound like the expansion chamber is too much back pressure causing the whole exhaust system to stall itself out....its worse on a cold start, but once i get the motor warmed up nice, it still happens at low to mid range.....top range still does ok for the time being. when this happens, it feels like the motor is going to lock up. and when i accelerate i can hear a high pitch ringing....(could be because i didnt take quite enough out of the piston skirt and getting a rubbing effect on the crank housing).....or the high pitch ringing could just be the natural sound of the expansion chamber and it likes to "sing" to me........i just dont know......any ideas out there in China box land?
 

Venice Motor Bikes

Custom Builder / Dealer/Los Angeles
Mar 20, 2008
7,266
1,797
113
Los Angeles, CA.
You changed the port timing when you shaved the piston skirt for clearance.
If the piston was touching the crank, it was obviously the wrong piston to start with. :(