Topic: K0 Carb tuning gurus....

[greenjeans]

69 CB750 sandcast.

Carbs are clean.  Real clean.  Original needles, and jets.  Float needles and seats are new.  Stock spec'd needles etc.   Everything is stock.
Carb boots and airbox rubbers are new and seal well.      Timing has been set, ridden, re-checked -  with a test light, not timing light.
Needle clip is on the middle notch.  It starts 1st kick or start button easily.

I have synched the carbs so it will idle pretty smoothly right at 1000 rpms.    The number 1 pipe, which was fine last week, is now running cooler and
popping through the exhaust in the 2000-5000 rpm range.

When warm, it idles smoothly and when given a big handful of throttle, it will really get up an go.   Everything seems good there.    It is the slow 1/4 throttle riding around town that is stumping me.   Pipes cools a bit and the plug is wet - not oily. 

Basically, it likes to idle and go "balls out"    It does not seem to like the 2000-5000 rpm range.  (only the number 1 pipe)

I don't think I've put enough miles on it to do a proper plug chop - plugs still look brand new (they are)

Any ideas ?       Too much fuel ?     I have the floats set with my homemade gauge. 

Could it be as simple as recheck the float in number 1 ?    Raising the clip (lowering the needle) ??      My weekend project will be making some clear tubes that I can check the "actual" level of the gas in the bowls.   I do believe they are set pretty accurately.

Is there anything obvious that I am over looking ?     

[Bob Wessner]

If you really want to have a look at actual fuel levels in the carbs, you might try this. I did something similar, but, as usual, a slightly more difficult approach to getting the tubing to fit. Next time I will try this one myself.

http://forums.sohc4.net/index.php?topic=37851.msg390105#msg390105

[greenjeans]

Simplest solutions always seem to work best.  Thanks for that link - you just saved me a couple of hours.

[Rigid]

Check the valve clearances.  Either side of spec will cause a host of problems.

[736cc]

  You will be amazed how much better it will run w/ 4 NEW #40 pilot jets ($8 each). Doesn't matter that they LOOK clean, new pilots always make a tremendous difference. Trust me.
  Simply put bike on centerstand and shut-off the motor w/ fuel turned-off to check the float level. Pop-off the bowls and get a rough idea who's level is high and who's low (sometimes its quite obvious), and tweak the floats. You want a little over 80% full. Not scientific, but this ain't rocket-science.
  Synching carbs is ez on early carbs. Hold it at 3-4000 rpm (use the adjuster at throttle) and adjust the brass screws on top of carbs until all 4 carbs at same level on vac gauges. Then play w/ air screw setting while synching, get the highest reading while adjusting until it starts to drop, then turn the oppositte way an 1/8 turn (all 4 carbs can be different; you just want balanced vac readings). Then set throttle play at grip adjuster to sloppy, set the 4 big idle screws so it idles around 1100-1200 rpm (I like these very rich running carbs set a little high. And they prefer full-throttle top-end blasts often to keep the plugs clean). Double-check for air leaks on all intakes.
  Oh yeah; check your coils. If you see sparks dancing while it idles in a darkened garage....
 
  And yes, valves must be set first or everything outa wack.

[greenjeans]

I'll check the valves again - I set them, rode it for 20 miles or so after the initial start-up and then drained that oil and re-checked/set the valves.

I'll try the pilot jets while I'm at it - I have some new ones from a kit I bought a while back (not Honda, but I'll give those a shot)

Think it might be a good idea to lower the needles 1 notch while I'm in there ?   

Thanks for the tips -

[736cc]

Leave the needles in middle stock position. They only need changing on extremely hi-mile bikes that have worn-out carbs.