A question for you Colortune users ...

[Steve]

I had the pleasure of using a Colortune yesterday for the first time. The first bike was a 750 with VM carbs.
Got to see the color changes along with the RPM changes, all went perfectly. :clap: :clap:

Moved over to a 1000 with BS carbs. Tweaked the mixture screws, but did not see any color change. :-k
The only change I saw was some intermittency as I turned the screws IN, then blackness as they neared FULL IN.
As I went back out past two turns, the blue flame started popping back in, it was rather steady about three turns out.

QUESTION: Is it normal for the color to not change on the BS carbs?

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[Guest]

I've experienced the same "now you see it, now you don't" color shift on some of my carbs...

Worked like it should on my old 550L CV carbs (yellow to blue), but did as you observed (blue on, blue off) on my 750L CV carbs. Never could figure out why, both sets of carbs were dipped, & had with new o-rings.

Essentially I gave up using it because it seemed to be rather inconsistent IMHO.

 

[hampshirehog]

QUESTION: Is it normal for the color to not change on the BS carbs?

No, it's not. If you tweak the mixture screw on BS carbs you're doing the same thing as turning the airscrew on a VM (only the other way round) and the mixture is changing so the colour will change.

And this is why I really like the Colortune - it's telling you that something isn't right in your carb. Usually a bit of muck is the problem, or it could be a choke problem (worn rubber), a bit of wear, out of synch etc.

Trust your colortune, maybe not to set best colour (often going a bit more yellow can be better) but that bit of glass won't tell lies.

 

[Steve]

Well, I have only done the one bike with BS carbs, will do the other two tomorrow night.

There was no problem with carb sync. Not only were they JUST sync'd, the mercury sticks were still attached while I was using the color tune. :-\\\

I sort of expected a bit of a color change with the BS carbs, too, but the mixture adjustment screws only control the amount of a pre-set mixture, not just air or fuel. It was consistent on every cylinder, so I don't think that any individual carb would have been a problem. I guess I will have a better idea tommorow when I use it on "Junior" and "Angel".

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[1948man]

So how did Junior and Angel work out Steve? I'm experiencing the same thing you did.

 

[Steve]

That was quite a while ago, thanks for dragging back to the top.

Actually, I think I only checked the outer cylinders of one of them, but I can't remember which one.

I got the same results, that is, consistent color, then intermittent firing, then nothing as I turned the mixture screw in.

When the firing went intermittent, I could hear a change in engine speed, so I think I will save myself the expense of a Colortune and stick with listening to my CV-carbed engines.

 

[1948man]

I actually spoke a little soon after only checking one cylinder. I did get a transition from yellow to blue on the other three.

 

[81ZUKI75]

listening[/I] to my CV-carbed engines.

Well, I had the same results on both of my 750's . Unfortunately, I purchased mine in a combo offering with the Carbtune last year.

 

[Steve]

OK, you're way off here.

The Colortune is in use for such a short time and only at idle speed, so "heat range" does not really come into play.

The only important criteria is that the threads match so it will screw into the hole.

Because it's in use for such a short time, there is no opportunity for any build-up that would prevent combustion.

The non-firing is totally related to improper fuel mixture as the adjustment screws are tweaked.

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[Steve]

So the colortune isn't really worth much then?

As I noted at the beginning of this thread (almost 6 months ago), if I had a bike with VM carbs, I would definitely have a Colortune in my arsenal.

However, given the results of my (limited) experience, I'm not rushing out to get one. If one happens to come my way at a good price, maybe, but it's not nearly as high on the "want" list as it used to be.

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[bwringer]

I think it's important to understand that the Colo(u)rtune is not a device for precision tuning. It's a great way to get mixtures in the ballpark, but final fine-tuning must be guided by the bike's behavior.

On VM carbs, you have a very wide range of adjustment available. It's quite possible to be WAY off with very little movement of the air or fuel screws. So the Colortune is very useful for getting these carbs close enough to enable further testing. Usually, you'll end up going a little richer than best flame color at idle.

With CV carbs, the range of adjustment is quite narrow, and the Colortune isn't nearly as useful. The exception would be if you're trying to narrow down the choice of pilot jets for a new configuration. For example, if you installed a header and pods and ported the head, the existing data on carb setups might not address your situation, so the Colortune might be a way to assess this.


With the bike idling, blip the carbs (open the throttle briefly and let it snap back). If it takes a longer time than usual to return to idle, the idle mixture is too lean.

If it dips below idle speed and then recovers, the mixture is too rich.

You can get very close with this simple test (as long as the intake system is absolutely airtight, there are no exhaust leaks, valves are adjusted, carbs are perfectly clean, etc.).

If it bogs when you open the throttle, it may be either too rich or too lean. These do sound a little different, but it's hard to describe. However, your nose will usually tell you if you're too rich.

Next, it's time for a road test for the final fine-tuning -- see how the bike responds when pulling away from a stop and as it heats up. Also, check for backfiring under engine braking from high RPM, and how smooth it is when starting to apply throttle out of a corner.

If the idle speed climbs as the bike warms up, it's running too lean and may even have an air leak.

If it starts running rough at long stoplights, or has to "clear its throat" to pull away, it's likely too rich and is fouling plugs.

There are other signs as well, but these are the major ones.

I tend to have the idle screws set a bit richer because it smooths out the off-idle transition. Choke is still needed to start the bike, but I can ride away safely as soon as it starts, and turn the choke off after less than a minute.

 

[Steve]

I think you have hit it, Brian, as the adjustment on the CV carbs only controls how much of a pre-set mixture is admitted to the cylinder. Since the mixture is rather constant, it would tend to burn with the same color, which I observed. When there is sufficiently less of that mixture, there is simply nothing there to burn, hence the lack of ignition, which I observed.

I have a feeling that if I had changed either the pilot air jets in the intakes or the pilot fuel jets in the float bowls, I would have seen a different color during combustion, but still would have seen the same erratic behavior as the screws were turned in.

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[waterman]

I noticed a lighter blue when lean, darker blue in middle to yellow when rich. You are correct, as you go leaner, at some point the cylinder will not light up at all. The light blue may just be slight misfiring before blackout.

I tuned my 650 like Brian, slightly rich on pilots. Instant drive off is nice. Plus it will start at 32 degrees or less. May cut my mileage, but I think it is about perfect.

As much as you only use it at idle, rev it and watch the yellow color. Does give you a little perspective on how carbs work.

 

[Steve]

Does give you a little perspective on how carbs work.

I agree, but, having had the pleasure of doing a set of VM carbs, then almost immediately following that with a set of CV carbs, my hopes and expectations were a bit ... well ... dashed. If I had seen the same color change in the CV carbs that I saw in the VMs, there would be a Colortune in my tool box right now. Given the results that I saw, I will continue to tune 'by ear' on the CV carbs that I have.

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