Topic: CB350F Pilot mixture adjustment

[Evel E.]

Hello,

I've cleaned out my carburetors and fixed a sticking float and my bike's running much better as a result.  However, I 've read conflicting things about where the pilot screws should be.  When I took them out, they were all at 1/2 turn out.  In my clymer manual it says 1-1/2 turns out.  I've found a Honda manual that states 1 turn out.  I was thinking about trying to adjust them with vacuum gauge set, and checking the synchronization of  the carbs at the same time.

On the carburetors I've worked on the pilot mixture screw is an air adjustment screw, so in would be rich and out would be lean.  The rule of thumb that I've always gone by was to find the peak vacuum for each cylinder and assuming there's say a 1/4 turn range where you get this, screw it in so you're on the rich side of the sweet spot, for best throttle response.  I can't really find any information on which way the pilot mixture screw works on these Keihins.

-Eric

[MetalHead550]

If the pilot screw is on the air filter side of the carbs it meters air, in for rich.  If its on the side closest to the engine it meters fuel, out for rich.

Are you saying you hook up a manometer to the vacuum test ports, as you would to sync, to set the fuel mixture?  Never thought to try that and I wasnt aware that air/fuel mixture changed vacuum the way slide position does when you sync.  Oh yeah, Hi by the way.  Later.

[Gordon]

1 1/2 turns out is the factory base starting point.  Where it should be set for your bike depends on several factors like altitude, humidity, temperature, riding style, filter and exhaust type and condition, among other things.  There is an idle drop procedure you can perform that's supposed to get the mixture set where it should be for your bike, but every time I've done it I always end up running too rich. 

The best method for me has always been trial and error.  I go for a ride and take the screwdriver along, screw them in until it starts bogging, back them out until it's too lean, and then set them in the middle of the two.  You can do a plug chop to check your work and for fine tuning. 

[dusterdude]

the race car mindset is to hook up a vacuum gauge and adjust the mixture screws(adjusting one screw at a time) until you get the highest vacuum reading,then adjust the idle speed to your liking.keep adjusting the mixture for the highest reading and adjust your idle speed until you get it where you want it.