NOT a typical Hitachi carb issue...?

Okay, been lurking the forum for the whole spring while building my XJ750S into a caferacer (I know, I didn't start the project, but I'm finishing it)

Anyways, I have gone through chacals carb posts with a fine comb and still can't get these stupid HSC33 carbs to work properly.
When I got the bike I immediately noted that these carbs are... let's say interesting and checked everything. "Luckily" for me the previous owner already did something to the bike since the carbs had 43 pilots and 112 main jets installed, but as far as I know it had been run like that prior disassembly. Unfortunately all the original plastics, including the airbox were missing.

Welp here comes the part most already guessed: pods.
Since there was no airbox and this was a cafe build the only option was to put pods onto the carb rack. Opted for foam pods instead of true metal pods since apparently Yamahas really dislike the metal net pods...

Since I wrongly assumed the jetting was stock (now know it doesn't match to anything chacal's info really) I threw on a 120 main jets and after wet setting the floats and syncing the carbs I needed to switch the pilot from 43 to 45 to get the mixture screw around the 2-3 rotation area. Now the idle is spot on and synced.

The issue is the main jets and middle area. I always assumed that there was gonna be some dead zone between the transfer from pilot to needle circuit, but no matter the jetting or shimming the needle there's an severe burple/rich zone at 3k rpm. After that it pulls well, but I'm down to 112 main jets again and it still feels extremely rich at WOT and middle area.

To further confuse me after test pulls the 1 and 3 spark plugs are completely sooted up BUT 2 and 4 seem good/a tad lean...how? What's happening? Can the YICS cause this or what am I missing?

 

Have you done a compression and valve check? Little things can add up.

 

Yup, compression is good and valve clearances within spec (although I did check these before running the engine after it had sat for a few years). At the same time I had all covers off and checked the internals. Also checked the cylinders with a borescope and everything seemed spotless (engine only ran for 50tkm)

Today I lowered the floats about an 1mm (wet level is now about 2-3mm) and I'm down to 110# mains and from cold it seemed to run extremely well, but still blubbers rich when warmed up, but it's frustatingly close and way better anyways.
I'm fairly confident the pilot circuit is spot on as the idle and 0-10% throttle is about perfect. I plan to further adjust the pilot circuit with a lambda sensor after I get the carbs otherwise set.

After the test run the plugs are the same: 1 and 3 sooted up while 2 and 4 remain almost more to the lean side, which makes no sense to me...

I also noted that it couldn't hurt to inprove the air flow into the carbs by tossing the uni filter collars and currently printing a velocity stack style mounting collars for the filters. Pulled the dimensions outta my behind but let's see...

 

Forgot to mention that the unifilter mounts I'm manufacturing will remove any harsh angles in front of the carb intakes and will provide a total of 6cm of stack style tubing of which half sits inside the foam filter.

In my head this should inprove the operation of the carbs and in theory might lean the mixture enough to suit the current jetting...? Easy test anyways.

 

Update:
Went down to 108# mains and tried the unifilters with and without the self made "laminar flow" tubes between the filters and carbs. Tried lowering the floats down to 5mm wet level, and did a test run between every change and basically it went worse.

What throws me off is the fact that this thing is supposedly close to it's stock jetting with pod filters and it's still running extremely rich ..what gives?

 

Aaand took the carbs to church with all steps this time and found out an issue with the enrichment circuit, which is basically leaking. Lapped the plungers and wells and plugged the extra breathers on there and made sure the plungers aren't leaking by sitting brake cleaner in the wells.

Slapped everything back on the bike and...it's still drowning in gas and randomly picking up revs at idle. Tried it with new sparkies and now change. Can't find any intake leaks, vacuum systems have all been deleted and even the idle is all over the place. Real freaking weird...

Maybe it's time to let this one sit for a while because I'm just stumped at this point.

 

Picking up revs at idle sounds like an intake air leak. Check that your head-to-carb boots arent cracked, & that the clamps aren't worn out & actually hold.

Once verified, do a full carb sync for a really smooth idle.

Also pull your plugs and verify they aren't fouled or running too lean.

https://turbododgeparts.com/content/faqs/how_to_read_a_spark_plug.html

Also, poor running with stock jetting and pod filters is what we expect. Stock jetting on pods will never run right.

Pod filters permit a different amount of airflow than the stock airbox does, and so, one must jet the bike to match the pods.

When I got my XS, the airbox was gone and someone installed pods with stock jetting, which ran like shiat. I went on ebay, got a used/correct airbox and now she runs awesome..

Pods and bobs and bling and all of that is about how the bike looks, or maybe how you look on the bike... Personally, I only really care about how it runs and these bikes all run best with the stock airbox.

 

Thx for the input but it was mostly unnecessary if you had read the previous posts...

Sure the original airbox would be nice, but not worth sourcing especially now when the whole bike is built to a specific look/style.
Someone else started this project and has done a bunch of misc. crap on top of losing most of the stock parts - including switching the jetting into "something" which I now realize is from a generic rebuild kit. Pilot was 43# and main 112# which I mistook as being stock and replaced them with 45 and 130 and have since come back down by steps until it's now 45 and 108 AND still running rich /.

All possible intakes have been ruled out with an overpressure smoke test and none found. Also visibly gone through everything.
That said I did found out the culprit for the wandering high idle rpm: it was the throttle axle seals. The outermost seals were already switched into double o-rings and all the rest were.those proper V-rings BUT I took another blunder by checking them and deeming them ok by visually checking them and determining they wete soft and tight on the outside seats...what I missed was that they were all almost 1-2mm loose on the axle itself. -> replaced all the rest with suitable fat o-rings and no more wandering idle + they synced great.

All this done the bike runs richer than ever. Apparently Hitachi carbs don't require as dramatic up-jetting than Mikunis and I now have way too large jet on the pilot at least. According to data I can find and crosscheck these euro spec XJ750's should have 40# as pilots and 104# mains on the outer two and 106# on the inner two cylinders.

After my holiday the trial and error continued...