Topic: Pilot Screw vs Fuel/Air Screws

[garrettmiklautz]

Hey guys, just a quick question as i can't seem to find a definitive answer. Or I'm an idiot.

I've got a 77' 750 and just wondering the stock specs on the Air/Fuel screws (4 brass) ones.. as well as the pilot screw.
I have the Clymer manual and it shows how to adjust the 'Pilot Screw'. So i think i can handle that portion..but Im getting a bit confused between the two and which one does what function.

If someone can clear this up for me that would be greatly appreciated!

Thanks.

[Airborne 82nd]

You did not say if it is a K or F it may not matter. But first off the Clymer manual is OK but the factory service manual is better. You can download it here for free.
http://manuals.sohc4.net/cb750k/
It has a lot more info. on the carbs.Maybe Flybox will chime in? He and 2 or 3 others know these carbs very well. Do you have the stock PD carbs? Some don't like these but I do mainly the pump. If you get it and the choke set up correctly they are sweet. It has been a while I will have to read my notes and get back to you if no one else chimes in. But I know they will.
 

[flybox1]

If you have PD carbs, turning the pilot screws OUT makes the idle circuit richer.
IN makes it leaner.

[martin99]

[quote author=garrettmiklautz link=topic=165003.msg1905087#msg1905087 date=1492053541
I've got a 77' 750 and just wondering the stock specs on the Air/Fuel screws (4 brass) ones.. as well as the pilot screw

Thanks.
[/quote]

You're getting a little muddled with the terminology. The four brass screws are known as the IMS (idle mixture screws) on the PD carbs. As Flybox says, it's out to enrich, in to weaken. Your manual should give you a setting, based on a stock intake and exhaust system, of how many turns out they should be from lightly seated. When you delve further into the black art of carbs (which it isn't really) you may find that the stock setting is not optimum for whatever you have for intake and exhaust. If you have anything other than a stock setup, i.e. Pods, different exhaust, I would suggest you post up what you have here as someone will probably have a similar setup and can give you a baseline setting.

[garrettmiklautz]

Thanks for the replies.

Its a 77' cb750k with a stock airbox, stock carb, and 4-1 exhaust.
There seems to be a pretty good write up in the Clymer manual regarding the pilot screw adjustment, but maybe those stock settings are not quite what i am looking for with the 4 into 1.

Does anyone know a good setting or starting point for the Idle Mixture Screws for a set up like mine?


Thanks again!

[flybox1]

Thanks for the replies.

Its a 77' cb750k with a stock airbox, stock carb, and 4-1 exhaust.
......but maybe those stock settings are not quite what i am looking for with the 4 into 1.

Why not?  Typically there is little to no adjustment needed with just exhaust, but we dont know if your 4:1 is baffled or not.
Have you done an idle plug chop to see what color the plugs are?   Might give hits as to the A/F mixture at idle....

[bochnak]

Here a "general" video and blog post about the topic:

https://www.howtomotorcyclerepair.com/how-to-size-your-pilot-jet-pilot-screw-explained/