Dgass

Hi i think i need help. In the heat today i have given my Terzo a right good thrashing as i was comming through the town i slowed down in the trafic selected 2nd gear perfictly fine. 200 yards later it sounded like the exhaust was blowing but i still had drive. ? engaged the clutch and the noise stoped selected 3rd perfictly fine and carried on up the hill a little concerned selected 2nd gear to turn into the road where i live to hear the same loud noise again!!!!

I have looked through the posts and have not found anyone with the same problem can anyone help as this sounds expensive Thanks