Reading a Colortune on an XJ

All,
I'm looking for guidance on how to read a colortune plug, so I can be sure its dialed in correct. Whats blue white vs bunsen blue is hard to tell, and hunting for it doesn't inspire confidence that I've ended on an optimal setting.

Here is what I'm getting. If it turn the screw until it seats, I see spark and no combustion plus the engine stumbles a bit. Slowly turning out, i reach a point where I see spark and combustion and I see blue, plus engine runs smoother.

But is that blue white or is it the holy grail bunsen blue? I think to myself Maybe its blue white and im still on the lean side, I should keep turning until I find the blue just before the mixture turns rich (aka yellow/orange). So I keep turning, but after many turns, the blueness hasn't changed even after the screw is well turned out, unable to achieve a visual rich setting. Within that range is the optimal setting, but how to dial it in?

Assume I'm back at the point where I first saw blue. Is it safe to say I would maximum be a dimes width away from the sweet spot, or maybe I'm there and done?

For XJ engines, based on your experience, what is the process you use to get the optimal setting using a colotune plug?

Thanks
Bob

 

"Bunsen blue" is bluish-white, sort of a translucent or neon-like "baby blue". Think of a natural gas flame. If you've ever used an actual bunsen burner, recall there is a movable slide that adjusts the amount of air entering, and by closing it off a bit you get a lot of yellow/orange flame (and probably soot)......that's "rich". Yellow/orange indicate incomplete combustion of the fuel,

Each of the combustion mixture levels (colors) has a range, so for example: the first two turns of the mixture screw out (from fully bottomed) may give you the "no combustion or bright white" result: these are stages of lean-ness. The maybe another turn to turn-and-a-half out gets you varying shades of blue. Beyond that you start getting blue-yellow or blue-orange flame, finally transitioning to mostly yellow/orange (to easily witness this color, once you are "in the blue", start cranking the choke on; this will richen up the mixture pronto).

What you want is to get all the way "thru" the blue range, and just on the edge of transition between fully blue and blue-with-yellow/orange. THAT'S where the "dimes width of rotation" comes into play. Anywhere else, it's just an old wive's tale (or a mis-understanding).

Your best results will be just slightly (a dime's width of screw rotation) into the yellow/orange side of the transition point.

BTW, if you simply cannot get the flame to ever get to the yellow/orange stage of combustion color----no matter how far out you crank the mix screw---- then that points to some other factor(s) at play: a partially clogged (perhaps internal to the carb body) mixture fuel circuit, a big vac leak, no air filter or airbox in place, fuel level set way too low, etc.

 

Crystal clear, thanks for the reply,
Its a good idea to deliberately enrich while observing the visual result. I can use that as a baseline to determine if I can reach it or if there is a fault condition.
Bob

 

In making sure that the "air" side of the equation was sorted, i did the propane bottle test and discovered two boots not seated properly at the airbox. Thanks for steering me in that direction.

I was able to discern blue with white as lean condition on two cylinders, and corrected it. The blue to blue yellow threshold i am still trying to get dialed it.

I will have another go tomorrow. I find that doing this at dusk helps with seeing the colors more clearly while running the bike outside.
Bob

 

I found my issue. After some reading through the threads, I realized I wasn't using the copper sealing washer for the colortune plug.
Using plug and washer, I was able to get to yellow by turning out the mixture screw then turned back to the threshold point where it turns blue.
Bob

 

I took it for a spin today and dialed in clutch and new rear brake, but it bogs. Cylinders 1 and 4 I couldn't get to rich with the mixture screw so may be lean (2 and 3 are good).
Propane bottle test passes no problem. Thinking.....check fuel level in float bowl. Saw this:


That is way too low for sure. Bike is flat on its centerstand. I spent a couple hours on float level adjustment before the rack went in, but its coming out and getting redone.

Since it likely contributed to my original issue, I thought I'd update the thread in case it helps someone in the future.
Bob

 

Yes that does look a little low.

I've never had much luck with propane, spray starting fluid or carb cleaner (make sure its the flammable kind, yes they make non flammable for some areas) works best in my experience. Your intakes look a little cracked which is why I'm suggesting an alternative method.