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Using a Colortune

  • Thread starter Thread starter rickt
  • Start date Start date
R

rickt

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Just purchased a Colortune for carb adjustment on the '78 GS750C. Wondering about the best approach - should I initially set the air needles for each carb at idle rpm and then run the rpm up to ? and adjust the fuel needle for a blue flame?

rickt
 
You should set the pilot screws at idle to get the blue flame.I think i will geta colortune for myself.Let us know if you are happy with yours.
 
The Colortune will only get you in the ballpark, but you still have to fine-tune by using the best idle method, by observing the behavior when you blip the throttle, and by test-riding.

A lot of people have the mistaken idea that a Colortune is a precision tool. It's very useful when you don't know where to begin following rejetting or an exhaust/intake change, but it's not intended nor useful for fine-tuning.
 
bwringer said:
The Colortune will only get you in the ballpark, but you still have to fine-tune by using the best idle method, by observing the behavior when you blip the throttle, and by test-riding.

A lot of people have the mistaken idea that a Colortune is a precision tool. It's very useful when you don't know where to begin following rejetting or an exhaust/intake change, but it's not intended nor useful for fine-tuning.
Click to expand...
I agree and disagree with your post. I agree that the Colortune is not a precision tool, there is a reason modern fuel injected computerized engines have sensors all over the place. I disagree that it is not useful for fine-tuning as perhaps that fine-tuning is subjective. I have to assume from your post that you are an experienced carb artist/mechanic and have tweaked enough carbs to know what to look for, listen for, and how things should respond. Unfortunately for someone like me who tore apart their first carb just months ago, that experience is not available in a few paragraphs. I tried, but only got so far.

For me, the Colortune is precise enough to eliminate a lot of guesswork, save me a lot of time, and not require the effort and possible expense to locate an artist/expert. Having the Colortune was much like life before and after a torque wrench - guessing before, much more certain now. If I were re-jetting and required maximum performance, I agree, the Colortune is only part of the picture, there is little substitute for experience.
 
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Good point -- the Colortune will get the bike ridable, and may even improve things considerably, but if you know what you're after, there are further improvements available through further tweaking and fine-tuning.

For example, my GS850 is set up a bit richer at idle than the Colortune likes simply because that makes the off-idle transition so creamy-smooth and controllable. I can get back into the throttle sooner in a corner and so I can go faster with less effort.

I've also spent a lot of time fine-tuning the float height. An adjustment of 0.5mm makes a big difference -- once everything else is perfect. And again, the goal is smoothness and improved controllability in the low-to-midrange.

My GS850G is certainly no torque monster, and engine-wise, everything is stock. But I can get back into the throttle sooner in corners and I have extremely fine control at small throttle openings, and that makes a huge difference when cornering hard. It also makes the bike much more pleasant to ride in any situation.
 
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i would love a colourtune, it may not be precise(and i agree with you 100% on that), but for someone who has been on countless gunnery ranges, small arms ranges, louda$$ c-130's plus wind noise on the way down and 1 police action; 1 war and several little excursions where hearing protection wasn't practical: it would be invaluable because i cant tell the small changes that well since certain dec. of sound i am deaf to. ask my blue pipes off the #3+4 cyl. how good that works. lol. seriously though for some of us it would be a great asset.
 
I agree that the colortune is not exact.

But to answer the question if you know roughly where your fuel screws like to be (eg I discovered from a lot of hit and miss between 1 - 1 1/4) then for ease of use adjust the air screws to the right colour and then fine tune fuel screws from there.

I found highest idle method quite inexact too and had previously adjusted my pilot settings from plug colour and throttle response. After six months of messing around I got a colortune and it basically confirmed that I was pretty close. Wish I'd bought it six months ago though...
 
Never tried a "colortune."

Mostly by sound in the past. From what I have learned with actual AFR measurement, when I have tuned a bike to a desired point, the bike actually does run a tad on the rich side as bwringer explains. I often find it starts up easier in cool mornings. "Cold Starts" like a little rich condition, basically what the choke does. In the summer I'll back it off, or the lean the idle circut a tad with the screws.

Choke on for a few seconds until the RPMS go up, then off on the choke, and let it warm up a minute or two. Good to go.
 
So would I be better off with just the carb synchronizer? I was thinking about the Motion Pro Syncpro (Z1 sells it cheaper than anywhere else!)
 
It is interesting to me the number of 79 GS750L's in this string! I wonder if they tended to have more problems with carburation? I know I would like to extend an invitation to bwringer
to come and enjoy the fall foliage in Minnesota and put on a clinic on how to get the L running as smoothly as he is talking about!! Just joking! But the overall progress does seem to be hard to acheive without a LOT of tinkering. I just hope I can eventually come close and not have the deceleration dying and the lack of power that has been happening lately. I am thinking that I have to get back in the carbs and reassess the float height and the possibly rust clogged pilot jet.
Oh well I did want a project not just a bike to ride only
 
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