Topic: Idle Mixture screw?????

[qcextreme]

just rebuild the carbs on my 75 CB750 Super Sport, but I Have one question, Idle mixture screw, how many turns out from all the way in. it has the factory header and pipe but the air box is  drilled out (about 12 small holes drilled on both side of the box to let it breath better) and it has a k&n filter, thanks for your time

[Warlock]

Greets,
According to the Honda service specs manual, the initial setting should be one turn from closed position....

[Terry in Australia]

G'Day Mate, just a dumb question, where are the holes drilled on the airbox? You know that the filter sits in the "bottom half" of the airbox, so any holes in the "Top half" will allow unfiltered dirt and debris straight in to your carbs? Oh you knew that? Sorry for interrupting then, ha ha! Cheers, Terry.

[qcextreme]

the holes are drilled on the bottom half of the air box, so you think one turn form out will work, even with the box beening drilled, how does it work , lean is out, rich is in, is this right..

[Gordon]

The factory setting for the idle mixture screw is just a starting point.  Each bike has to be tuned separately.  You have to account for differences in airflow, altitude, and even seasons. 

[Steve F]

I have almost the same situation, a '76 750F supersport, drilled airbox (compliments of the previous owner), and K&N filter.  I was having problems with the #3 cylinder gas fouling the plug.  It turned out that the idle screw was too far in (rich).  I backed it out to 2 turns and it's running (almost) perfect now.  Some more tuning is still in the works, and I'll be moving the needle clips up a notch (lowering the needle) to do some more experimenting, hopefuly to help out the top end (higher rpm) from running too rich.

[qcextreme]

Steve, so your running 2 turns from out, is that on all carbs or just that one, let me know it moving the needle helps

[Steve F]

"Steve, so your running 2 turns from out, is that on all carbs or just that one, let me know it moving the needle helps"
I believe it was just #3 carb, but I was twiddling all 4 carbs, and they're in the area of at least 1-1/2 to 2 turns out on all 4.
It'll be a couple of days before I can get back to it to try the needle adjusting and the necessary re-synching. I'll let you know.

[dpen]

If you're going to do it-do it right. Do you have a remote tachometer? Yes?-hook it up No?-clean out your ears as you'll need them.
Screw the screws all the way in (not tight-just so they bottom) now back them out one & a half turns. Start the bike & begin with carb #2. Slowly wind the screw out until the tachometer shows the highest revs. Move the screw in & out in slight increments until it sits steady on the highest revs. Do the same with the other carbies.
Have clean ears? The bike tacho is not accurate enough so, with no remote tacho you have to do it by ear. Wind the idle up slightly so most of your cam chain/clutch noise disappears. Start with carb #2 again & play with the screws until you can hear (or think you can) the motor at it's highest revs. All this takes less then 10 minutes. Synchronise the carbs & then FANG IT!