backfiring

[Gray17]

Hi Nigel what do you suggest think ones you sent in kit have 17.5 pilots in at mo, poster said 1 or 2 sizes up?

[Ultim8pc]

Hi Nigel what do you suggest think ones you sent in kit have 17.5 pilots in at mo, poster said 1 or 2 sizes up?

You have the correct pilots for your carbs.
But if you want to go bigger then next up is 20.
I have stock:
https://airevalleyclassics.co.uk/mikuni-pilot-jet-size-15-to-22.5.html

[Gray17]

Thanks for reply, was awaiting original posters reply as to what sizes he used and how the bike now runs, as you know I've had plenty of issues with mine and despite spending a fortune on it still doesnt run correctly. I have no idea if the larger pilots will work or whether i need 20s or 22.5s, this is a problem its guess work, hence hoping he had gone tbrough that process of trying the 20, 22.5 etc and what if any effect that had on the running. He stated that it ran fine on old fuel assume meaning leaded, now with this E10 or E5 it doesnt.
I have no problem buying the jets if that will solve the problem but not really convinced it will. I may try backing the airscrews to 2 or 2.5 turns out see of that improves matters, but appreciate it will only allow as much fuel as the jet size restricts.
Thanks

[Ultim8pc]

Thanks for reply, was awaiting original posters reply as to what sizes he used and how the bike now runs, as you know I've had plenty of issues with mine and despite spending a fortune on it still doesnt run correctly. I have no idea if the larger pilots will work or whether i need 20s or 22.5s, this is a problem its guess work, hence hoping he had gone tbrough that process of trying the 20, 22.5 etc and what if any effect that had on the running. He stated that it ran fine on old fuel assume meaning leaded, now with this E10 or E5 it doesnt.
I have no problem buying the jets if that will solve the problem but not really convinced it will. I may try backing the airscrews to 2 or 2.5 turns out see of that improves matters, but appreciate it will only allow as much fuel as the jet size restricts.
Thanks

Does it run better at low revs with the choke slightly on? If so then it's a lean condition you are seeing. So upping the pilots may work even if it doesn't make sense.

[gray]

check the springs on the autoadvancer aren't weak - if they are, so the engine is running on full advance even at low revs, this will cause low speed hesitancy and good high speed running.
With a strobe , check the timing at idling speed, then open the throttle slowly while watching the marks. By 2300-2500 revs on a z900 ( about 3000 on a Z1etc) timing should coincide with the "full advance " mark.
If you are getting full advance much earlier, then the springs are U/S. But they're cheap from Z power