Topic: Early Honda CB750 question...

[fast eddie]

I'm working on my bro's '69 CB750, and put in a set of later model carbs with mounting plate and mech linkage in place of the individual cable operated slides. It's essentially the same carb, but I noticed the air screws are different, they are hollow. These carbs came to us with NO SPRING UNDER THE AIR SCREWS, and the screws fully seated, not backed out 3/4 to 2 turns as you would expect an air screw to be adjusted. It doesn't seem to make much tuning diff if you back them out, either. Is fully seated the correct treatment?

[pjlogue]

The hollow air screw helps prevent over rich idle.  Be sure your idle air circuit inside the carb body is spotless.  Use a soft wire to chase the passages and blow out with compressed air.  I believe 1 turn from lightly seated is your base setting.

-P.

[ekpent]

 Yep-one turn out is what I use also. What size main jets are in there? K0's came with 120's. Carbs should have a model number stamped on them also which can give  you an idea as to what year they originally were used on if your interested in knowing..

[fast eddie]

thanks for the replies, so I take it I need to put springs on these screws and I'll start them at 1 turn and go from there. Not sure on the jetting, I'm having some mid throttle bogging so I'll be getting back into that and prolly raising the needles a notch or 2. It's got a KN element and 4 into 1 exhaust, so stock jetting will need to be richened a bit. My bro suggested I swap in the jetting from his original carbs, I'll start with that.

[pjlogue]

If you use aftermarket springs you want to make sure the end of the wire of the spring is smooth and won't catch and plow up brass or carb body metal which will then get into the internal passages.  The OEM springs that came with the carbs have tapered ends to the wire so the spring will sit at 90 degrees when stood on end.  All the aftermarket springs I have seen are not tapered and chew up the needle or the carb body.  If you use aftermarket springs, take a dremmel with a cut off wheel and smooth off the sharp end of the spring at both ends.  Getting chunks of metal in the passages is difficult to remove.  Ask me how I know. 

-P.

[fast eddie]

Well, I got around to putting larger main jets(went from 115 to 125) from the original carbs in(duh, should've noticed when I did the swap)and it made all the difference. Runs like I remembered it running back in the good ol' daze...

[fast eddie]

Didn't need any needle raising, thank gawd!