Topic: What does this do? PD42A Carb from 1978 CB750F

[Shikai2070]

What does this adjustment screw do? Seems to press up against choke linkage/arm

[bryanj]

Puts the revs up when you pull the choke out

[Pielz]

Yeah that's your fast idle. Important to set it properly. Your choke will either do nothing at all if it's too far out, or be super hard to pull and when it finally goes, revs will shoot up to 6k if it's too far in Ask me how I know lol took me forever to figure that out

Your manual should have the info on how to set it btw. I put some sticky bearing grease on there if it sticks a little. Did on mine at least. Don't know how long that'll last though

[michtag]

Ha! yes, important to set it properly and it took me a while to figure out it was my problem (see http://forums.sohc4.net/index.php/topic,180711.0.html)

Manual instructions (for CB550, but it should be the same) as follow:

1. Remove the tank (if you haven't already, of course)
2. Pull the choke knob out fully and turn the adjusting screw until it touches the stopper
3. Push the choke knob in and turn the adjusting screw in 2 1/2 turns. Fast choke idle speed: 3000-4000 rpm

cheers
/m