Seems Lean, but plugs are black. Thoughts?

Okay all you amazing carb tuners, I have one to baffel the masses!!! I came into a 81 xj550. It had been parked since 1989 and only has 7,000 origional miles. As you can imagine, the carbs were extermely gummed up. I spent a good 8 hours dissasembling, rebuilding, and reinstalling the carbs. I bench sync'ed them, and put them back on. I used a YICS tool to then further sync the carbs. This was difficult as the engine would race as I tried to adjust the idle up to 1500 RPM's. Being smarter than the average bear, I richened the carbs up knowing that the racing is usually caused by a lean condition. I also checked for airleaks at the manifold, and it seemed okay. Now, here comes the weird part. I popped my colortune in and tried to adjust the mixtures back down. All I can get is a blue color. I bring the mixture screws almost all the way out, and still can't get it to go orange. I then remove the plugs and find them a little black and sooty which would be indicative of a rich condition. All of the jets are stock, and I'm running the stock pipes and airbox. All boots are hooked up, and the is an air filter in there. Any thoughts? The engine gets really hot even with my leaf blower cooling it while tuning. How hot is too hot?

 

My plugs always are sooty after idling for awhile too. Even a lean mixture makes some soot, and I suspect the plugs don't get hot enough at idle to clean themselves.

If you can't get the mixture to go rich you have too little fuel or too much air.

Too little fuel is likely caused by unsuccessful cleaning.

Too much air can be caused by leaks or the butterflies open too far. You get above 1200 rpm and the mixture screws seem to have very little effect.

As far as too hot - I have done very long syncing and colortuning sessions. I can set the idle to 1100 at the end of the session then take a couple mile run on the freeway. After the run the idle will creep up a bit. My conclusion, it gets hotter going down the freeway than it gets idling all day.

 

I actually cleaned them twice cause I though I might not have done it right the first time. OH they are clean!!! Thing idles at 1000 RPM's perfectly too!!

 

I think you're "idling" partially off the main jets. hence the reason you can't get it to go rich with the mixture screws.. as MiCarl pointed out, your butterflies might be open too far. This happens when you're still a bit out of sync, but close enough for it not to race (sync being out of whack is another common cause for racing idle).

Did you bench-sync the carbs?

 

you pretty much need to get up to 4500-5000rpm for a steady bit then it the kill and check the plugs. at idle they will appear darker than they should. If you have no hesitation across the board from idle to WOT quickly and good off the line pull you are doin alright.

 

I did bench sink the carbs. My racing idle is completely gone at this point, and really isn't much of an issue. There is no hesitation at all on the throttle. Thing pulls really hard, and sounds great. Just seems odd that I could be running so lean on stock jets. Great questions though. They are things to recheck.

 

Okay so I ran it a higher RPMS to burn the soot off the plugs. That worked, and they are a little white. So, I'm running lean and have the adjustment screws way out. Thoughts?