Topic: Air/fuel mixture

[Deltarider]

https://youtube.com/shorts/IDXKzuAKEPg?si=XUNBKx9I0PD13Wln

To me it sounds like less than a true 1000 rpm.

[jlh3rd]

sounds fine to me

[eastern]

Plugs were a bit sooty after a ride today.  Maybe felt a bit rich.  Went to 1 1.4 turns out.  Will see how that does.

[jwurbel]

So you are taking the position that out is lean?  I will be interested in your results.  The in lean, out lean, in rich, out rich never seems to get clarified regarding results.  I am aware of screw location relative to engine side vs air box for carburetor settings. Not sure on your carbs where your adjustment screw is at.  I contacted Keihn some time back re: my CB 750 k2 carbs and posted their comments earlier.  In was rich, out was lean which is contrary to Mark.  This is NOT a criticism of him or his extensive writings on this subject.

[eastern]

I hear you.  Just going to try it at basically stock setting for a bit and see how the plugs look.

[dave500]

dont over think this simple adjustment,its not critical to the running of the motor once under way and using power,however the idle mix on these carbs does add to the overall fueling but only to a minimal amount,some carbs for example mostly on cars have a more complex system where the idle mix cuts out once driving along and adds no more fuel,if you think you have a rich condition when running i doubt its from the feeble fueling added from those idle mix screws.

[PeWe]

Small adjustments can make it.
From running well and screaming to the feeling of a wire attached to the front end that a high powered winch pulls hard 

A car gives the kick in the back.

[willbird]

So you are taking the position that out is lean?  I will be interested in your results.  The in lean, out lean, in rich, out rich never seems to get clarified regarding results.  I am aware of screw location relative to engine side vs air box for carburetor settings. Not sure on your carbs where your adjustment screw is at.  I contacted Keihn some time back re: my CB 750 k2 carbs and posted their comments earlier.  In was rich, out was lean which is contrary to Mark.  This is NOT a criticism of him or his extensive writings on this subject.

That would kind of tell us that the screw is letting more air bleed in as opposed to letting more fuel in ??

Bill

[eastern]

Fair enough Dave500 and PeWe.  I went back to the 1 1/4 more because when I went to 1/2 out, it was before the carb cleaning/sync and I wanted to start closer to recommended baseline.  Haven't had the chance to spend time working on mixture since the sync is complete, but that and the strip/clean was the money.
I need a few hours to install new spokes on the rear, then will take it for some proper shake down rides.  Hopefully in the next couple of evenings.
At city speeds, it is currently running flawlessly. 

[M 750K6]

On the question of whether screwing out or in leans the idle mixture. 750K6. I have plugs 1 and 4 showing slightly sooty. I unscrewed the idle screws on these 2 carbs to 1 1/4 turns out. I then went for a ride. I had difficulty starting the bike from cold. The bike was surging / missing at idle and in 1st and 2nd at low speed, below 3,000rpm and I had occasional exhaust popping when engine braking. This went away when I returned to 1 turn out.

I read those symptoms as running leaner at 1 1/4 vs 1 turn out, especiallythe exhaust pops.

After nearly a year trying to understand and fix the two slightly sooty plugs, I've been through the carbs, tappets and ignition and once the carbs are clean the bike has always run fine at exactly 1 turn out. As the plugs don't foul and as far as i can tell the exhaust pressure is the same on all four (my compression tester doesn't cope with the deep narrow spark plug position) I've decided to just live with it. Provided you're not running too lean, on a 50 year old bike, if it runs well, bank it as a win!

[dave500]

yours should have the early carbs,the air screw is behind the slide,turning it in cuts off air=makes it richer and visa versa,have yours got the hole drilled in them,i like the solid ones better,bit more control i think?you can solder them up solid.

[HondaMan]

Something to remember with these OLD carbs: they are soft metals. The mere act of having turned in the screw(s) tight (or snug, hopefully, instead) widens the hole of the taper just a bit. So, in many cases, the 1 turn setting is slightly more than 1 turn out, now.

Note that this change doesn't happen with the PD type carbs that use the tiny O-ring and flat washer to seal against: that was why those were created for these bikes, as the US DOT was really beating up Honda over how 'mushy' the settings actually are in the roundtop-type carbs. The O-ring and tiny washer are the seat in those later carbs, so 1 turn today is the same as 1 turn in 1976.

[Deltarider]

They look like this.