1977 carb jets and idle adjustment

[skrivan]

hello again....i've been working on my bike again.  it's running now, but i cant seem to get the idle right and it bogs don when i gun it.  less bog if i have the choke on about 1/2 way pulled.  it sure starts right up now....that part is good.

i put a 4 in 2 exhaust (was a beatup 4 in 1) and i wanted pod air filters 'cuz the black box is just so ugly.  i pulled the carb again and saw that it had 120 jets.  i went back to 115's and re-assembled it.  i must have someting not right, still.  it idles at 3000 and the thumb screw is all the way out.  i set the needles at 1 1/2 turns out.  float levels all checked in at 14.5 mm.  i havent gotten into the timing yet, but i dont think that's going to change anything on the idle or am i wrong there, too?

i also get quite a clank in the engine....i think it might be the cam chain tension bu havent tried any adjustment on that.  i also need to check the valve clearances.

i saw on another site that some guys check the float level using clear tubes on the drain nipples.  has anyone here tried that?

anyway, i'm getting more psyched and even have paint (original candy red) which i'll apply after i get this thing running better.

thanks for any advice on the idle questions....joe

[Piute]

   Used the tube trick to check mine was way high,was redid and great now,with scews at 2 1/2 turns
         everthing stk.

[Lucky 1]

IS it a CB750?????

The problem with the tube method of setting the (EDIT..sorry )float level  is how do you know how high the gas should be?
With a float gauge you set the float and that controls the height of the gas n the float bowl.

On almost all honda engines (generally speaking) the float bowl is about 3/4 full when full when the float is adjusted.
It will NOT be 2 mm (.078) from the top edge. Thats too full.

When a engine is idling high it is either running LEAN or the throttle mechanism is stuck somehow.
Or the choke is on, and it is not warmed up.

[Piute]

  The choke well chokes in more gas ?? air box on causes a lot of choke too,by simply putting clear tube on over flow it levels out and can be seen if high or low is all nothing complicated. ,you still have to get the floats right,AND they(carbs) don't have to be in/on the bike ,put a towl on a bucket and make it eas on your self. There is hardly any noise compared to way it sounded before and I still havn't sync them.
   Will try to see if Paul can get A vid for sound also.

[skrivan]

hey lucky...noits a 77 cb750. the manual says 14.5 float level. this carb is the 'keyhole' style. so if it idles high, then i am running lean (too much air, not enough fuel). does turning the pilot screws change this and should i turn them out or in to run more rich? does timing effect idle?

[skrivan]

i got it running better today.  i went back to 120 size jets and spent more time getting it all set up right---float in #3 cylinder seemed a bit out of spec and it was easy to re-set it.  the clear tube test showed things were close but not exact...not sure what would be done to fix that...anyone??

i put the original ugly airbox back on too.  i think the pods look better and i might go back to them but they are kind of hard to get on and i dont feel like screwing with them again.  tomorrow i'll go for a real ride.  the pic is of the bike when it was on ebay....i should take a few more and post as things happen.  i'm going back to the original candy red color, polished the tank logo platestoday and i have the side covers all primed and ready for color.  once i get the thing running better i'll pull the tank for the 50th time and get it prepped and painted too.

[Lucky 1]

14.5mm=.570 thousandths.

But I can make it even easier than that for you.
With the carb upside down:
Just take a steel ruler and lay it on top of the idle jet.
That is where the top of the floats should be. that is .570

Nice tip eh???  LUCKY

Oh make sure you have new float needles if they have
not been replaced in the last two years.
Or if the bike was sitting.

Install a #42 idle jet and your problems will be gone. #35 is way too small.
Set the mixture screws at 3/4 turns open. One turn will be too much.

The main jet mostly controls the bike at WOT -NOT idle.
Idle is controlled by the idle jet and the mixture screw up to 1/4 throttle.

[Lucky 1]

You get the level of the gas in the float bowl RIGHT by setting the float CORRECTLY.