Cannot figure out idle adjustment

[unitedhow]

It seems so close to running properly and it's honestly becoming more depressing than exciting to work on.

I start the bike with the choke out and after about 30 seconds rpms increase so I close it some and again until it's all the way in. At this point the bike idles at 12-1400 rpm.

If I give it throttle it revs through fine but as it comes back down it sticks at 3k rpm. If I reduce the idle speed screw it slows back down to about 1k and I screw it back in to 12-1400.

From reading other posts this seems like a symptom of being lean (right?) But if I unscrew the idle mix screws it gets too rich and fouls the carb (currently 2.25 turns out). The carbs are very clean (4 or 5 cleans boiled and blown... All new jets, needles, seats, floats, float pins) bike is all stock battery is good and charged/charging.

Floats are set at 27.3 +/- 1 mm as per service manual and posts I've read. Had them at 26 but the crankcase kept flooding with gas (having them higher say 27-28 would stop that right? Not increase the odds, it was before I put in the new seats and needles)

I can't find any air leaks while it's running. Bike is a 1980 xs400g special II. Help.

 

[xschris]

A few things, did you replace the butterfly shaft seals or removed them before the boils? Have you synced the carbs with a manometer? If your floats are set at 26mm (brass floats and taking measurement with no gasket on the carb) they should not leak gas unless your float valves are bad.

 

[unitedhow]

Thanks again xsChris I was just nervous since it happened 3 times before I replaced the valve assembly. I reset them to 26mm (quadruple checked them). Rode it around until it was warm adjusted the mix and idle speed then synced the carbs.

Not one hanging rev, no pops, no backfires idled at about 12-14 (hard to tell exactly on stock gauge). As long as it doesn't flood overnight I think it may be good.

I did notice that it wants to inch forward a bit and that's clutch but is that a symptom of it being too tight or too loose at the engine, or could that be undone at the handle?

 

[xschris]

Adjust it at the engine first then the handle.

 

[unitedhow]

I have new symptoms that I'm having difficulty figuring out. The bike was running fine. I drove around about 5 miles in the city with no problems. I went from a ride today. Started the bike (choke out) and took off planning to push choke in as needed. The first time I let off the throttle the bike died. I pulled off to the side pushed the choke in and it started up again but the idle was really low and sounding like it wanted to die again.

I've also been noticing that the idle doesn't surge with the choke out as it warms up like it used to. Now if the choke is out I have to push it in or it seems to start bogging down.

The top end is also loud. Kind of a knocking sound.

(As a side note can the oil cap retain the gas smell though there is no more gas leaking into the oil? The cap smells gassy but the oil I wipe off of it does not also the crankcase doesn't seem to and the level has not changed at all)

These are the plugs
L. Bottom R. Top

 

[xschris]

Plugs look a little rich or oily. I would check your valve clearances but that noise should be a tap and not a knock.