Sir:may i ask you a question about motorcycle.My problem is that, 4stroke engine 125cc Honda,when i ride on the high way is OK,but when going down to the hill,it made sound like a gun fire,i have change new plug, and adjust the air screw . but it still make the sound like gun shot.Please help me to cope whit this problem.
If my English is not polite to you,pardon me for my mistake.
i am from myanmar(burma)
Matt
The bike is backfiring. If you are backfiring constantly while slowing down, then your jetting is slightly off. You need to run either 1 size smaller or 1 size larger jets. Being lean and being rich will both cause backfiring.