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...

 

For most of the rest of the world, a combo like that is stock for the 650cc carbs.

The HSC33 carbs (if that is truly what is on your bike) used much leaner (smaller) mains and pilots but the air jets were changed and the main jet needle was massively richened up (probably to compensate for the much leaner fuel jets). The emulsion tube was also different than the HSC32 series, as well as the vac piston spring (which probably contributed to a greater and/or quicker rate of rise of the vac pistons and hence the richer main jet needle...........).

It's actually unusual to have any of these HSC series carbs run rich in stock form, unless:

a) too large jets or incorrect main jet needle
b) mixture screw is turned far out from proper position
c) choke plunger valves are not fully seated, or, there is a flaw (gouge, etc.) in the choke plunger valve seat machined into the carb body.
d) fuel levels in the bowl set way too high
e) some combo of the above.
f) someone has drilled out fuel jets to a larger size or installed one of those "performance" jet kits (which typically also involve drilling the vac piston air bleed holes to a larger size). NOTE: aftermarket "performance" fuel jets may not be marked with the correct Hitachi "size" designations. Hitachi fuel jets (but not the air jets) are marked in millimeter sizes: for example, a #120 fuel jets should have the drilled hole diameter or 1.20mm, a #130 should be 1.30mm diameter, etc.......a 340 pilot jet would be 0.40mm diameter). Aftermarket mfgs. might inscribe "43" on a pilot fuel jets, but measurements show it to actual be a size #50 (for example).

TOO LEAN is the issue most commonly encountered.

Maybe so.....and certainly not part of your current rich-condition issue.....but I would strongly suggest that you eventually replace those o-rings with the correct v-seals.

 

Hey chacal, I truly appreciate the reply!

Yeah, this thing quickly turned from an easy project to an headache caused mainly by the carbs.

The bike is without a doubt an XJ750S euro model, with the HSC33 carb rack.
No idea about the real model year since my country designates model year by registration and it's registered 1986, but it still has the same color carbs. Fuel inlet is between the 2/3 carbs, breathers between 1/2 and 3/4 and the extra breathers at the mixture screw base on every carb, which makes me certain these are HSC33.

The air jets on each one are 225# and 70# which should be stock. Now I also replaced the fuel jets into 41# pilot and 108# main since my own research points to the Hitachi's not being THAT sensitive to pod filters.
It seems to be way better mixture wise on the 41# pilots as it's no longer eye stinging rich...

That said, the throttle axle seals were a miss. Throttle is sticking bad and keep experiencing random intake leaks, although can't pinpoint the location. At the moment I can't proceed with adjustmens since it's all over the place, one second it's choking and the next it's pulling 4k while sitting on it's own.
Only thing I am sure is that it's not leaking from the boots or YICS...

And yes the enrichment plungers are still causing issues by not seating correctly. No idea how to fix that issue other than blocking them off completely for now. I might need to abandon these Hitachi's and get something else to get this thing working properly...

 

Update on the current plan:

So I know I could have get the correct seals from chacal, but living where I do those seals won't get to me for this riding season so....

I did an inquiry run around my city and found a set of 8x12x3mm actual axle shaft seals to go. I plan to install these onto the carbs "wrong way around" to keep air out rather than fluids in. In my head these proper shaft seals can't be worse than the original "V-seals" right...?
These seals are a bit too fat with that 3mm thickness, but the excess is on the outside lip which will poke out of the carb body -> exacto knife will take care of that ~ 0.7mm excess that would be binding on the shaft spacers.

On top of that I wen't ahead and bought a new arsenal of lapping compounds and will take my time lapping the enrichment plunger seats on each carb + thoroughly test them after that they absolutely do not leak.

These will be the final steps I'm willing to take with these carbs and if the enrichment plungers still leak these carbs are scrap anyways...

 

This is now turning into a project thread, but I need to vent...

So 2 out of 4 carbs now done. Took my time with each one, completely dismantling everything and spending about half an hour per enrichment plunger of lapping. Tested the plungers with penetrating oil (the extra breather nipples on HSC33's came handy on this) and neither one I lapped had any kind of leaks even with air pressure. So the choke/enrichment circuit shouldn't cause issues after I get the other two worked on.

Also took my time to soak and clean everything again, just to be sure. Got the new shaft seals on the carbs, which did need some modifying since the seats on the carb bodies are actually 11.5mm and the seals outer diameter was for 12mm hole, but damn they should be tight now. Also polished the throttle axles and rounded off any sharp edges on them before installing them on the carbs with plenty of grease.

I have to say I'm pretty confident on these seals working like a charm and the axles now move with basically zero friction...

 

Update:

Got all of the carbs "refurbished" so to say. For some reason the 4# carb enrichment plunger was leaking really bad when I originally thought the 1# was the worst with the couged plunger seat. On 4# it took about four times the work to get it lapped and sealing properly but got it done.

Finally bench synced the carb rack and took the effort to reposition the throttle flaps so that they have the exact same opening on the lower edge + exact same amount of pilot orifice showing.

Now I need to find the motivation (and time) to get the rack back on the bike, synch them and get on the road to see if the needle and mains still need work...

 

Wet set float levels before putting them back on the bike.
Just to make certain all 4 floats are shutting off

 

I've done this for half a dozen times already, mainly because there's contradicting info on what the levels on this spec bike should be. Tried the 1mm wet level first which was just ridiculously rich and now I have them wet set at 5mm(+/-1mm).
Took dry measurements before I dismantled everything and verified that the levels were the same while rebuilding... But you may be right, I might wanna wet set them again - again just to be sure...

Luckily this is a cafe bike now so it's pretty straight forward taking the carb rack out and back in again. Done it so many times in the last month I lost count...

Speaking of the float valves: does anyone have concrete info if the HSC33 should have rubber tipped needle valves or brass? Because this thing has the rubber tipped ones and again, contradicting info if these are original or some BS aftermarket ones...

 

Hitachi float valve needles were originally rubber-tipped; many (but not all) of the Mikuni carbs from that era used metal-tipped needles. Thru the aftermarket, you can purchase metal-tipped needles for the Hitachi HSC32 / 33 series carbs, and that's actually what is recommended for people who live in an area that has fuel (gasoline) with a high (10%-up) ethanol (alcohol) mixture as the available fuel (this is a very common mixture in North America). The reason for the use of metal-tipped needles is that they are far less prone to seizure within their seat, which is much more likely to occur with a rubber-tipped needle.....especially in the presence of alcohol (which will cause most types of rubber to swell a little or a lot, depending on the type of rubber used to make the tip).

So the metal-tipped needles greatly reduce the chances of fuel delivery issues due to a needle that gets seized in the closed position (no fuel!) or seized in a partially or fully open position (flooding).

 

Thanks @chacal, that confirms that everything inside the carbs should be correct. Clearly the previous dude bought some kinda kit for the carbs since needlevalves, seats etc. were new/spotless. Shame that he didn't bother to replace the seals while at it, but it is what it is...
Fortunately we still have 5% ethanol gas still available and that's what I use on all my gas guzzlers for obvious reasons. (Daily drivers are all EV, so never need to buy any other type either)

Got some motivation finally to test the current setup and determined that I'm a dum-dum...

Screw me sideways but after installing the newly sealed carb rack on and getting the engine warmed up the erratic extremely lean condition came back...LUCKILY I had switched into clear gas tubing and realized that my forward tilted tank(to allow adjusting) was low on gas and the rear mounted petcock was running dry...filled it up and repositioned the tank more vertical to continue adjusting. /end of dum-dum

That said the idle is now THIS CLOSE to being spot on but still a little bit lean while the screws being at 4.5 rotations open, any more open and it just chokes out so guess that's the end of adjustment for these screws. No matter, they shouldn't be that far open anyways.

Just ordered 42 and 43 pilots and will test with the smaller first. Didn't bother to test drive it for the full throttle or middle area because of the limping idle and living in the city, but stationary/against the clutch it seemed to be pretty peppy and revvy.