XJ750 Seca conundrum - can't lean it out

Hey folks.. Been a while! I still have my Seca, and it still runs great, keeps my two XS11's company.. But this post is not about it.

So now I'm wrenching on a 750 Seca that belongs to a friend of a friend.. Having a really odd issue with it.
It ran kind of rough, and was almost impossible to start, so I thought I'll do the usual.. Valve clearances, carb tuning etc.

The problem: I cannot get it to lean out. It insists on running very rich.. Not to the point of flooding, but close. Black plugs all around.. Even with airbox boots disconnected, to rule out bad air filter).
It idles fine. Starts fine (now, anyway). As soon as you rev, it starts loading up.
It even coughs a bit when hot with all four plug wires removed

What I have done so far:
-Checked and corrected valve clearances (a couple were really tight, the rest just out of spec)
-Rebuilt the carbs -- the owner took it to a shop, and the mechanic there did a half-ass job installing a carb kit.. Mains were 122's, pilots were 43's.. Float levels were non-existent (they all stuck up at about 45 degrees). Jets are all stock now - 120 mains, 40 pilots.. Air jets and compensator jets are stock. Y-13 needles.. Nice, clean emulsion tubes.
-float levels adjusted a bit on the lean side (about 4mm)
-Rebuilt the carbs AGAIN.. This time with a whole another body. Same results.
-Had vac gauges connected the whole time.. Carbs synced.
-Fiddled with pilot mixture screws.. All the way in til the cylinder goes away, then back til RPM picks up, then back in a bit. Double checked a couple with colortune plug.
-Check compression.. Right around 115-120psi.. Not perfect, but not the worst.
-Replaced plugs, which are (and were) stock BP7ES.
-Cursed a bit. Had a whiskey.

The ONLY thing that I can think of.. It has some aftermarket turnout mufflers.. Headers and collector appear to be stock. Could shitty aftermarket mufflers make it run stupid rich like that?

Could timing be off?

Any suggestions would be much appreciated. This is far from my first XJ wrenching experience.. Been messing with them for about 12 years now. This one got me stumped slightly.

Thank you much

 

plugs black and wet or black and dry?


timing could be off but can not be set. what tci does it have? part number please or color of label
5G2-82305-10-00 T1D14-06 red label?

could be the needles were shimmed leaving main jet open

 

Plugs sooty black and dry. Needles are stock, not shimmed. Even tried my dynajet needles, dropped a notch.. same results. TCI is red label TID14-06.

 

black and dry can be lean
is it a stock air filter?
air jets installed like this


what did you see with color tune plug?

jet washers flat not cupped?

 

Air filter is out of the picture.. Airbox boots not even connected. It billows smoke out that smells like raw fuel, so definitely not lean. I triple-checked the air jets, and they are where they're supposed to be. 225 in the front, 80 in the middle.

 

washers flat on jets or cupped?

could be worn mixture screws but i doubt all 4 would be bad

4mm is in spec for fuel level 3mm +- 1mm

 

I annealed and flipped the copper washers on the main jets.. Was concerned about the cupping as well. Mixture screws are brand new, with new o-rings. Turning the screws in effectively kills the cylinder.

 

check the timing you can not change timing but it will tell you if tci is not working correctly

 

I was gonna try swapping the TCI off my good 750 tomorrow. Hell, maybe even the carbs.. Will post results. Thank you for the suggestions!

 

Well, went ahead and tried swapping the TCI.. No change.

 

easier to try his tci in your bike first

 

Do you have a set of numbered drills, or a set of jet gauges?

My guess is that the fuel jets were drilled out when the exahust was put on, but not marked as such.

 

check the enrichment plungers they may not be sealing well

 

Will check the plungers.. Though it would be odd that two racks would have identical sealing issues on all four bodies.
As for the jets.. The 120's and 40's are the original jets from my Seca, which was re-jetted for a high flow air filter and a mac 4-1 exhaust. They've never been drilled out. The jets that were in this bike are from an ebay rebuild kit.. i promptly set them aside, as i don't trust them.

I'll try his TCI on my bike, as well.
i'm also gonna knock the mufflers off.. a buddy of mine with a '79 XS11 had the same problem, and it ended up being caused by a set of Mac 4-2 turnout mufflers.
worst case.. i'll swap carb racks from my bike, to see if the problem follows the rack or the bike.

i was thinking maybe failing coils, too.. but once again, the symptoms are identical across all four cylinders. not impossible, but improbable. also, the previous mechanic purposely dropped the fuel level in the bowls to where they would only fill about half way, to compensate for the rich condition... treating the symptom instead of fixing the problem and all that.

thank you, peeps.

 

Another member here had the same issue working on another members bike, drove him nuts until he checked the jets.

 

did you happen to check the cam timing ?

 

I haven't yet. I was wondering if that might somehow affect it. Is cam timing a possible culprit?

 

no need for a light, cam timing is the "C" on the crankshaft and the dots and marks on the cams.
the one i saw was one tooth off and it ran but badly, what led us to look into the cam timing was excessive blowback thru the carbs when it ran.
have anything like that?
depending on which way it was off the blowback might not happen

 

Nope, no backfire or blowback. Just runs very rich with stock settings, and loads up/shuts down at half to full throttle, chugging smoke and leaving the plugs solid black and sooty, but not wet. Idles just fine though.

 

try the mufflers