I first got this bike running with unrestored carbs borrowed from my other cb500. With these stock setup carbs fitted it ran almost perfect without changing anything despite having a 4 into 1 fitted!
So I sent the original highly corroded carb set that came with the bike to harisuluv to be reconditioned. They came back in pristine condition looking almost brand new.
I started with the original jets (100/40) and needle clips #4 position and initially still had the 4 into 1 with a rather loud muffler fitted. At first the bike would only run properly if it was stone cold - after 30 seconds it would start to blubber like as if the choke was left on full and soon after the plugs would stop firing and when removed, were found to be wet with fuel which had to be dried off to get them to spark again!
I bought second hand 4 into 4 pipes for it one by one hoping that they would make the tuning easier.... but it still took me years to get it to where it is now 
(on my low income I have to save up the money each time before being able to buy new different size genuine jets)
Very interesting. Do you know what your float height was before the overhaul? I am wondering if it was higher than the stock spec like mine was (= higher measured float level = lower measured fuel bowl level).
I seem to recall reading some other threads here where someone had experienced that their CB500 was running excessively rich after overhauling the carbs. Usually, those threads stopped before the problem was resolved. Starting to wonder if maybe there is some variable at hand related to float heights. If maybe the spec varied with years and/or markets… causing people going by the 22 mm spec to create this problem in some cases when they 'correct' the float height.
To summarize from my prior posts, I received my bike with ~24 mm float heights, stock jetting, and an aftermarket 4-1 exhaust (rusting out). And it actually ran okay in the initial 1/4 throttle range. And then after overhauling the carbs (to include correcting the float heights to 22 mm) and installing a new aftermarket 4-1 exhaust, my bike ran excessively rich in the initial 1/4.
And to save someone having to ask the question: Yes, I set my float height per the shop manual procedure. Starting with the carbs in the normal upright position, I slowly tilted them forward until the float tang just touched the float needle spring pin, without depressing it. Then I measured the float height using a dial caliper set to 22 mm - from the carb bowl flange to the highest point on the float pontoon. I considered the height correct when the caliper just touched the pontoon, without moving / depressing it. And I did that for both pontoons of each float. And I actually went through that process twice (once during overhaul, and then a second time when I had the carbs off again later).
First let's check if we all agree on what is a turn out. In my book one turn out is a 360o turn.
In mine as well. With the air screw seated, I made an alignment mark on the air screw and carb body. So as I back out the screw, I am 1 turn further out each time it aligns with that mark. I am typically making adjustments a 1/4 or 1/8 turn at time, over multiple riding sessions / days, etc. The marks help keep track of where I am and prevent rounding errors from accumulating (so that four consecutive 1/4 turns made at four different times always adds up to one full turn, etc). A few times along the way, I turned the air screws all the way in, counting the turns, just to confirm I was where I thought I was.
What I hope, is that you haven't turned out the airscrew so far out to achieve a highest rpm at idle. That may be common practice for most motors and will work fine for them, not for ours. I can turn my airscrews out as far as Mrmunsel has and I'll be rewarded with a silky engine that purs like a kitten. But the bike won't accelerate well anymore.
I do understand these bikes are supposed to run rich in the pilot circuit. I made my adjustments based on feedback from the bike (behavior, performance, and plugs). Not while idling nor based on idle speed / quality / etc.
Mine was excessively rich with the stock carb configuration - fouling plugs to the point of causing missing in a matter of minutes. Very blackened plugs.
The bike runs great with the configuration noted in my prior post. If anything, I suspect the pilot circuit may actually still be richer than necessary with that configuration. I can open the throttle quickly under any conditions I have tried thus far, and it handles it well (no hesitation, etc).
Since my prior post, I have tried turning the air screws further out. I wanted to experience what it was like when the pilot circuit was leaner than ideal (not necessarily lean, just not as rich as it should be, etc). And ultimately, I want to understand if the 2 3/4 setting was best or if there might be an even better setting. It seemed apparent to me when I had gone too far out. Cranking open the throttle too much / too fast sometimes results in a hesitation. Noticed popping on deacceleration more often (was pretty rare at 2 3/4). This was at 3 1/2 turns out. I am no carb expert… but it seemed like the bike is telling me it likes the air screws somewhere between 2 3/4 turns and 3 1/2 turns out (with the current jetting, intake, exhaust, etc). I have started going back the other way now (at 3 1/4 right now, but haven't ridden it yet). Performance / drivability was great at 2 3/4, but mileage was increasing with them further out… so just trying to find the best compromise between the two. It could be that 2 3/4 was the best compromise already... but given my inexperience with these bikes - I won't know until I have tried some settings beyond that.
My gas mileage after my carb overhaul was consistently 30-32 MPG US***. With all air screw settings I tried on the #40s. Ditto on the #38s. That didn't start improving until I got to the #35s. At 2 3/4 turns out on #35s, it was consistently getting 34-36 MPG US. I had several fill ups with that config. I don’t have a full tank with the air screws at a consistent position that is further out than 2 3/4 on the #35s. On my last tank though, I had the air screw at various settings between 3 and 3 1/2 turns out - and it got 38.8 MPG US. That is the best since the rebuild (prior best was 35.95 MPG at the 2 3/4 turns out).
***Note: That is only counting tanks that included mostly typical riding for me. For reasons I can only speculate about, my bike actually achieved better mileage early on in the tuning process on tanks that largely did not reflect my typical riding. Lots of WOT runs and hard acceleration, trying not to stay in the first 1/4 too long to avoid plug fouling, etc. Far less steady state cruising than typical. More typical conditions for me would be pretty much the opposite of what I just described. Lots of time in the first 1/4 throttle, occasional spirited runs, occasional hard acceleration to merge with highway traffic, etc. I am guessing that because the pilot circuit was so excessively rich at that point, I was actually better off from a fuel economy perspective on tanks where time spent at lower throttle angles was minimized.Since I had to turn my air screws so far out on #35s to get it running well, I have been considering going to #32 pilot jets. I was pretty close to ordering some last week, but decided to hold off for now and get some more time on the #35s. My concern is whether there is any overlap in metering from one available size to the next (in this case, #35 to #32). For example, if I went to #32s, would there be an air screw position that provides similar metering as my current #35s at ~3 turns out. If not, then I anticipate the pilot circuit will end up too lean with #32s. Also, I don’t want to make this small carb orifice any smaller than it truly needs to be. Plus it is running so well after so many iterations of adjustments, I am hesitant to make any major changes unnecessarily… just enjoying riding it for a little while.
technically each cylinder will require a slightly different setting.
Yes, the air screw settings I reference here are my ‘nominal setting’. I start by adjusting the carb air screw settings in tandem (1/4 or 1/8 step across all four, repeat as necessary). Once I get it to a setting that seems good, I start tweaking the cylinders individually based on the plug appearances. I have consistently found on my bike, #1 and #2 look the same with the same air screw setting. While #3 needs the air screw slightly further in to achieve similar appearance. And #4 a little further still. The exact difference in air screw setting across the cylinders varies (seems to require less difference when the air screws are further in, etc).
