SOHC.co.uk Forums > CB500/550
Hanging Idle and poor throttle response.
3scs:
There’s definitely a spider in there I can see them in both sets of f2 carbs I have but only when I take my glasses off
Sesman:
Bet you can’t. Try passing a 0.2mm then .3mm wire through a clean jet. If it goes through, there is no spiders web.
McCabe-Thiele (Ted):
It might not be relevant but back in the 1960 blocked jets on Vauxhall Vivas caused misfires due to them blocking up - the factory fix was to produce similar jets fitted with a screen filter as a remedy.
Eventually they just fitted better in line fuel filters that fixed the issue completely.
3scs:
--- Quote from: Sesman on August 22, 2022, 10:45:57 PM ---Bet you can’t. Try passing a 0.2mm then .3mm wire through a clean jet. If it goes through, there is no spiders web.
--- End quote ---
exactly push any wire through and there will be no spiders web left I know what I can see in my jets it’s definitely there 😊
Skoti:
"I've seen visibally oval main jet needle seats on SU carbs regularly on cars - more so when BL spring mounted the main needles on later designs."
Ted makes a interesting observation regarding oval wear on needle jets because it's apparently not only engine vibration that wears them but also the inlet vacuum effect.
When accelerating hard on full throttle the vacuum draws the needle forward hard against the needle jet and then the back and forth motion causes this oval wear pattern which was also evident on my CB750 when I changed my first needle jet set at 24k.
It's obvious that I'm not the only one on this forum that worked in the motorcycle trade in the seventies or others who perhaps professionally repair that stuff nowadays so to them please forgive me for offering this advice.
The needle jet and needle control the correct amount of fuel passing through the main jet up to about 3/4 throttle opening, after that the main jet size defines the correct fuel supply.
My point is that no amount of fiddling with slow jets will considerably alter rich running problems on the road as the slow jets only controls engine idle and the transition to the needle jet and main jet fuel supply and is effective up to around 1/8 throttle opening.
Worn needle jets alter the air/fuel ratio and cause rich running and possibly throttle hanging etc.
Damaged slow running jets enlarged by cleaning with oversized wire probably won't improve things either...
Please correct me if you think I'm wrong, I'm never to old to learn!
Regards
Skoti
Navigation
[0] Message Index
[#] Next page
[*] Previous page
Go to full version