During deceleration/over run I get a popping/backfiring. The engine also hunts when I'm at low load/low revs. It also jerks when I'm just rolling the throttle - such as rolling up to a T junction and gently pulling away without stopping. Everything is fine when I'm loading up the engine with some revs. I never had this issue before with the bike.
So far I've changed all the jets, diaphragm and seal and o-rings - everything on the bottom of the carb(I got the Carb Kit from the TTR shop. I've also changed the inlet rubber from carb to cylinder head(Old one appeared fine- cheap Chinese replacement went on ok). I also tried new fuel. I still have the problem. I seem to remember reading the choke can leak air in if seals are damaged - but I can't find anything on this when I look on this forum again. I had suspected the inlet/exhaust valve/seat had burned out/leaked- but I get loads of power. I've done a compression check on a suitably warm engine and it came back at only 70 psi - worrying- but as I say I'm getting loads of power above 1200rpm- I suspect I'm not getting the o-ring on the end of the compression tester to seat and seal properly. I'm going to clean this area and see if I'm going to get a better seal and then have confidence in any compression reading I get. But I’ll be amazed if there is any major issue with the engine(knackered valves, bores, head gasket) because my bike pulls like a train above 1200rpm.
Unless someone else has verified such major issues on strip down when their bike has still had loads of power above idle? If the compression reading still comes back low after I’m certain I’m getting a good o-ring seal I’ll strip down the engine during winter but in the meantime if anyone has any ideas or guidance I’d appreciate it.
Also I’ve seen the cheap Chinese 4 valve set for £40 and complete gasket set for £14 on eBay – has anyone any experience of them? They are £160 and £100 respectively elsewhere
Do you remember which jets you used as replacements? A 52.5 pilot seems to help your condition. You may also need to fine tune the needle. By symptom I would guess you are lean near idle but you may want to move your needle up one and down one clip land to test. Keep us posted.
