Honda-SOHC
SOHC.co.uk Forums => CB500/550 => Topic started by: alan on September 13, 2019, 03:57:03 PM
-
does anyone know the correct needle valve setting for a 1973 Honda CB500K1, I've fitted new carb sets but I dont know if any of the previous owners have messed about with the setting so I've left them the same. The problem is it seems to be a sluggish, it also takes ages to start from cold?
-
The slide needle is middle of 5.
For starting. Check your float levels. And slow running jets.
Also check for air leaks between carb and head.
During the summer. Mine starts from cold without choke.
In regular use.it should start easily
Sent from my SM-A750FN using Tapatalk
-
Also check plugs. Plug caps.etc
Sent from my SM-A750FN using Tapatalk
-
The slide needle is middle of 5.
I have also looked for the spec needle position. Can't find it in the manual, where did you find it? On both the UK carb sets I have it was set to the 4th from top. I changed it to 3rd from top on the set I use and may try it in 2nd from top.
-
They generally sent them out with the clip in centre notch when delivery took place, making specification adjustment with main jet size.
Needle would be adjusted to accommodate local running condition of temp, altitude etc.
You can probably run them a little leaner on current fuels as consistency of octane and overall rating would be more refined now as opposed to supply in 1970s. Making two down from top notch probably a pretty accurate position if all components are clean and in good condition.
Starting without choke normally suggests it's a bit too rich for ideal combustion.
-
Have a look at the scheme I have compiled if you like. Note that there's only one source, an American booklet, that specifies the jet needle in 4th position and airscews 2 turns out. If that has been the case from the beginning or a later recommendation, I don't know. That booklet was edited in 1977... I seem to remember that in those years, US was particularly interested in low emissions at idle.
-
Those American settings may be in response to particular riding conditions assessed in that market. Perhaps surging or hunting at constant throttle at 55mph constant highway running?
If they open the idle screw more it would alter the slope of fuelling for that range and shift the point at which maximum flow from the small jet in comparison to throttle slide height occurred. That point moving upward would delay the need to get the main jet going so moving the needle downward on the slide would correct that transition by reducing the overlap of the two. Otherwise known as "mapping" in current fuel injection language.
The idle circuit and screw position is not an absolute, the screw just alters the angle of fuelling slope as it responds to both vacuum and inlet tract air volume. That's within the flow parameters made by the air and fuel passages and sizes fitted.