colortune and carbtune arrived now I have more questions!

Well I finally ordered the Colortune/Carbtune pro combo from Morgan. It arrived the other day and, like a kid with a new toy I immediately warmed the beast up and started tinkering.

I had just checked and re-shimmed the valves. All are within spec. I had also tuned the pilot mixture by ear but had not done any plug chops. The bike was running well and holding idle at 900 fairly smoothly with only the occasional arrhythmia. All plugs looked pretty rich when i pulled them but I had not done a proper chop.

I installed the colortune in #1 and fiddled with it till felt competent reading the flame then tuned all 4 carbs. There seemed to be a fairly wide range of what might be considered blue or yellow. I tuned lean until there was no hint of yellow at all then enriched until I started to see yellow and tweaked just a bit lean. She stumbled on start up but held idle once warm and hesitated accelerating from idle. Good throttle response over 2krpm but popped just a bit in the exhaust on let off. Chopped at 5.5k and all plugs still looked very rich so I installed new plugs and started over.

I re tuned all 4 with the colortune and new plugs with the same performance as above but now all plugs were completely clean. No coloration at all. I re-tuned by ear and then used the colortune to see where things were. I think I have the rich/lean break figured out now. All cylinders appear to be just a bit past perfect to the rich side. Idle is fairly smooth at 8-900rpm but still have the occasional off beat stumble. I cannot get the idle screw completely open. I can turn the idle down to 6-700rpm and it will hold but another tiny tweak and she dies. Could this be be because the bench sync wasn't done properly? Throttle response is great with just the slightest hesitation off idle.

Now here's what's puzzling me. Plugs 1,3 and 4 look just the tiniest bit rich. #2 is still clean like it has never been installed. I ran the colortune in 2 again to verified that it was firing and played with the mixture again to just be sure that the pilot screw had an effect. Everything looked good. Chopped again with the same results.

What could cause this?

 

Did you order from the UK, and how long did it take between order and delivery?
Mine's still "on the way"....

 

I ordered it on 5/31 it was in my mail box on 6/9 and yes, I ordered directly from Morgan in the UK.

 

You are trying to set your idle to low for starters. For my 1982 seca, the manual says to set it at 1050 rpm (and it's +/- 50 or 100 rpm, I can remember which).

Also, as you colorturn, you need to re-sync your carbs. Bench sync gets the carbs in sync relative to each other with respect to butterfly opening. Synching on a running engine syncs the actual cylinders to each other, as the cylinders are not identical. I suggest getting a yics tool (you to have yics on an 81 right?) and doing a synch. There are also suggestions that you can plug the yics passage with a Marvel Mystery Oil soaked t-shirt, but I think the tool from chacal is worth the $40. Or you can make your own.

You can repeat the colortune procedure if you want, or just work from plug chops. But at the end of the day you need to always sync, since adjusting mixtures of one cylinder will affect the vacuum it pulls relative to all the other cylinders. Do all syncing and colortuning at the recommended idle speed (1050 rpm)