Topic: Carb adjustment

[Nick13]

Hi I have a quick question about carb adjustments. i have a 1973 cb750 and when I first start it, it idles at a normal speed around 1000 rpm but as it warms up the RPM's steadily increase to about 3000 RPM can anyone tell me how to adjust my idle speed as simply as possible, cus i have never done any carb work before and really dont want to take it to the shop for somthing that could be simple.

thanks guys,
Nick

[TwoTired]

A cold engine simply doesn't atomize fuel as well as a warm one. Requiring a higher idle setting that opens the carbs for more fuel flow.  Later carbs have a coupled fast idle cam that does this while the choke is applied.  Your carbs do not have this extra cam.  The main idle knob is adjusted for idle speed when the engine is fully warmed up.  The opertor has the option of holding the throttle open during warm up to keep the engine running.  Or, tweak the big main idle knob for desired idle speed while the engine is warming up.  Some Hondas have a throttle friction adjust knob under the throttle grip.  The tension can be adjusted to hold the throttle open some during warm up.

It's the nature of the beast and 30 year old technology.

cheers,

[BobbyR]

All of these bikes are a bit cold blooded. I have later model with the fast idle cam, but I do understand what you are talking about since I don;t like running the choke longer than necessary. Your best bet is to set your idle speed using the knob to about 1,500 RPM since above that your engine braking is diminished. When she is cold just keep her running with the throttle.

[medic09]

If it will reassure you any, now that I *seem* to have gotten my carbs straightened out, I start and warm up in several short stages over a space of 3-4 minutes.

I have to start with choke and a bit of throttle.  I use my throttle lock and let the bike warm up like that for about 1-2 minutes around 2000 rpm on the tach.  At some point, if left alone, it starts to speed up all by itself as the gas atomizes more efficiently.  With choke now off, I warm up another 2-3 minutes with the throttle lock holding the re-adjusted throttle (after releasing choke).  Again, it will start to race by the end of this as the gas continues to atomize more effectively as the engine warms up further.

In the morning I've got the bike warming up in the driveway while I'm trying to finish stuff in the house.  I know it needs my attention when my wife yells "it's taking off by itself again!"   

Now that warmer weather is here, the whole process is easier, shorter, and quieter.  (Time to change to colder plugs soon...)

[Nick13]

Thanks for all the help guys 

-Nick