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Carb sync/carbtune pics

Larry D

Larry D

Forum Sage
Past Site Supporter
Our intrepid bwringer stopped by today (12-26-08) with twr1776's carb tuning tools in hand and made gave my bike a Christmas present !

My bike and I say Thank You !

Here's some pics and a video.


This is what we're starting with.


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Here's the video. Somebody tell me it linked okay, please. Got it all sorted out and the bike's is running great ! Thanks again.

http://s345.photobucket.com/albums/p364/Larry_D/?action=view&current=MVI_0028.flv
 
I just got my carbtune the other day. Haven't had a chance to use it yet as the running bikes are winterized and stored somewhere else, and the bikes in the garage aren't running yet. :( Maybe soon though. Pretty slick little unit.
 
so that colortune is where its at, huh? i think im going to buy both.
 
thanks for doing the pics and vid
I have never seen a better demo of how this thing works
very well done
 
cyberdork said:
What's happening in the video?
Click to expand...


The carbtune is basically a see-through spark plug. It allow you to see the spark and tune as needed.

Too much blue is rich and too lean is bright yellow, almost white.

We tuned until they were yellow with just a slight hint of blue. Maybe a touch rich, but I know where they're set and can make a quarter turn later, if needed.
 
Very cool, I received my carbtune and colortune about two weeks ago. As soon as Nessism can rescue me enough to get my carbs back together, I'll be trying mine out.
 
In the video (that's my right foot...), I cranked the idle mixture screw out about half a turn to demonstrate how the flame color turns yellow, then in again to show it turning a nice blue.

You want to get the flame a nice blue, then make it a little richer than that for best idle and throttle pickup from idle. I made the flame nice and blue, then backed it out 1/4 turn from there. We may do some more tweaking once we get a break in the weather and can test-ride the bike, but it's very close now.

In the video, the spark appears to be missing a beat every so often, but I think that's sort of an artifact of how the video was recorded.

We got the mixture screws very close simply by listening to how the engine idled down and how it reacted to "blipping" the throttle rapidly:

  • If it "hangs", meaning that it tends to return to idle very slowly, that's a sign the idle mixture is too lean.
  • If it "dips", meaning that it goes below idle speed (or dies) when you release the throttle and then returns back up to idle speed, that's a sign the idle mixture is too rich.
  • A lean or very rich idle mixture can also cause stumbling when you blip the throttle.
  • If you have an intake leak, you might also notice the lean symptoms of a "hanging" idle and that the idle speed increases as the engine gets hotter. An intake leak also makes the engine run much hotter than it should.

To use these indications, you have to be in the ballpark already -- clean carbs with clean idle passages and a properly sealed intake system, along with a healthy ignition system. If one of these factors is off, then twiddling the idle screws doesn't tell you anything.


Those brass vacuum port tubes are from my mercury synchronizer. The Morgan comes with these little plastic tubes that are sort of a pain to deal with. They work fine, but it's just easier to grab hold of the brass tubes.

Lastly, you'll note that the vacuum readings aren't totally identical. I think I ended up getting the 3/4 readings a little closer after Larry took the picture, but the important thing to know is that you can't ever really get this absolutely perfect -- you'll make yourself crazy trying to get everything exact.
 
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Larry D said:
The carbtune is basically a see-through spark plug. It allow you to see the spark and tune as needed.

Too much blue is rich and too lean is bright yellow, almost white.

We tuned until they were yellow with just a slight hint of blue. Maybe a touch rich, but I know where they're set and can make a quarter turn later, if needed.
Click to expand...

Is the color chart different for different models with the colortune? i do know that the carbtune has two models.

I only ask because when i did my tuning according to the color chart yellow is rich and blue is correct mixture, light blue is lean. I have the twin carbs.

I know some like to have a yellow center ring with a blue outer ring to run slightly richer rather than leaner to prevent detonation etc.

For example when you blip the throttle it turns yellow because of the extra fuel admitted to the cylinder, then returns to blue when idling steadily.
 
Last edited:
Yes, a nice bright blue is the "correct" idle mixture (most complete burning), but you get the best throttle response when it's a touch richer than that.

The same applies to any engine with carburetors, from motorcycles to cars.

If you leave the mixture a bit lean, it'll stumble when you try to pick up the throttle. If you're riding hard in the twisties, you need the off-idle transition to be smooth as silk so you can ease into the throttle sooner.
 
bwringer said:
Lastly, you'll note that the vacuum readings aren't totally identical. I think I ended up getting the 3/4 readings a little closer after Larry took the picture, but the important thing to know is that you can't ever really get this absolutely perfect -- you'll make yourself crazy trying to get everything exact.
Click to expand...

But it sure is easier to get the readings DAMN close with the Carbtune. I love that the readings don't bounce around like with a mercury stick. Nice, steady readings:

 
Luckily there is an acceptable range they all have to be in to be correct.

It's about 1/2 an inch on the scale so long as they are all in this range it makes a world of difference.
 
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