I have the same probs although i have a 16 valve, 1.5 litre, and mine bogs down evrytime i switch into a new gear. This ALWAYS happens after i run it for bout 10 -30 minutes. I cant figure it out. Im gonna switch my sparks and my fuel filter and see what happens from there. Someone told me it was the clutch, but i know its not cause it engages pefectly. Anyways i really cant drive for more than 1/2 hour because it does this.