Anyone use a Gunson Colortune?

gpzkat

gpzkat

Joined
Sep 15, 2020
Messages
486
Country flag
I got a couple of nice free '83 Suzuki GS1100Es from a local guy, and in the huge pile of parts was a Gunson Colortune with a 14mm adapter. Cool! I went for a 45-minute ride on my N15, and stopped to do a little back-and-forth idle mixture adjustment on the single Mikuni VM34 when it was warmed up. Halfway between lean vs. rich RPM drop gave good results but I could tell by the plugs that it was a tad rich - tan on top but a bit of carbon black on the main 'ring'. With the Colortune, the revs dropped about 100 RPM when the visible flame just got blue. About 1/4 turn out on the idle air mixture screw. I tried to do a video but messed it up. I'll ride it and check the plugs to see the results (and take a video). The Colortune is very easy to use. The bike's running great, I'm just dialing things in as best I can.

Anyone use a Gunson Colortune?


Anyone use a Gunson Colortune?
 
I use one. It is only good for setting the idle but you can get it very close. I put the perfect bunsen burner blue slightly to the ritch side.
Be careful of the ceramic stem as it is very fragile.
 
gpzkat said:
I got a couple of nice free '83 Suzuki GS1100Es from a local guy, and in the huge pile of parts was a Gunson Colortune with a 14mm adapter. Cool! I went for a 45-minute ride on my N15, and stopped to do a little back-and-forth idle mixture adjustment on the single Mikuni VM34 when it was warmed up. Halfway between lean vs. rich RPM drop gave good results but I could tell by the plugs that it was a tad rich - tan on top but a bit of carbon black on the main 'ring'. With the Colortune, the revs dropped about 100 RPM when the visible flame just got blue. About 1/4 turn out on the idle air mixture screw. I tried to do a video but messed it up. I'll ride it and check the plugs to see the results (and take a video). The Colortune is very easy to use. The bike's running great, I'm just dialing things in as best I can.

Anyone use a Gunson Colortune?


Anyone use a Gunson Colortune?
Click to expand...
I have one, got it like you. I've tried it and it does work, but my old-school technique is faster and IMHO, produces a better idle. When I have nothing to do (rare!), I'll have a look once I'm happy so it's decent to verify.
 
What is the blue flame supposed to represent AFR wise?

I have not used one. Butt dyno man all the way. Mine happens to be accurate. Verified many times.

Have fun with it.
 
The bunsen burner blue is a perfect burn. AFR. Too white and it is lean, too yellow and it is too rich. There is a clear view in the cylinder when it is firing by the special sparkplug view adapter to replace a regular sparkplug. Nothing too high tech. been around for a long time. Again only useful for setting idle.
 
CanukNortonNut said:
The bunsen burner blue is a perfect burn. AFR. Too white and it is lean, too yellow and it is too rich. There is a clear view in the cylinder when it is firing by the special sparkplug view adapter to replace a regular sparkplug. Nothing too high tech. been around for a long time. Again only useful for setting idle.
Click to expand...
Thanks I should not have posted. I'm testing a locally made bourbon. Never drink and derive.
 
CanukNortonNut said:
The bunsen burner blue is a perfect burn. AFR. Too white and it is lean, too yellow and it is too rich. There is a clear view in the cylinder when it is firing by the special sparkplug view adapter to replace a regular sparkplug. Nothing too high tech. been around for a long time. Again only useful for setting idle.
Click to expand...
It's that limited application that puts me off buying.
I can set idle myself - now if there was something to help with "running circuits"...
So for me it's chop, chop!
 
robs ss said:
It's that limited application that puts me off buying.
I can set idle myself - now if there was something to help with "running circuits"...
So for me it's chop, chop!
Click to expand...
I'm not selling the product. I'm just telling you how it works.
each to his own.
 
marshg246 said:
I have one, got it like you. I've tried it and it does work, but my old-school technique is faster and IMHO, produces a better idle. When I have nothing to do (rare!), I'll have a look once I'm happy so it's decent to verify.
Click to expand...
Yep, was free and sort of 'fun' to see in action. With a single Mikuni, it's pretty basic to set up and all it did was confirm I was very close.
 
I used to use them
But as others have said they are only really good for setting the idle
Plus in a lot of old dirty running engines if you set the mixture to a perfect Bunsen blue
When you snap the throttle the motor can die
So you end up setting the mixture by feel
I have used them to see what the engine is doing under load by riding at night on an industrial estate looking down to see the mixture at marked throttle positions
 
If you have an ignition with idle stabilisation then you can no longer tune by ear, the idle stabilisation fights your tuning and is trying to regain lost revs at tickover. So my old unused Colortune is now back in use.
 
My butt generally tunes to a low F#. I haven't tested the color since high school but then it was a yellow flame. We found Bic lighters worked better than Zippo.
 
Mike40M said:
Never had an alcohol fuelled bike that idles.
Click to expand...
If you're talking running on pure alcohol, I have nothing to add.

Otherwise, all mine idle using E10 (only thing available). At cold start, no chokes installed, they idle at 700-750 and when warmed up, 1050-1150.

E10 gas, Tri-Spark timed at 29-31 degrees targeting 30 but not being anal, correct Premier carbs properly installed and synced and the air screws properly set. As bas said earlier, perfect ColorTune, snap the throttle and they die - air screws in slightly and they do not die - that is always my last test no matter what and it is tested once warmed up. IMHO, Commando Engines, in general need to be slightly rich, at least for common street use.
 
My idle mixture test is whether they burble annoyingly on the downhill to the mail boxes. At that point the engine is still relatively cold. I find if set them so they idle best, the almost-off throttle surge is annoying. Set a little lean and that goes away. But it's a fine line. If set too lean they're harder to start. Once the engine is fully warm the condition is noticeably more pronounced. So I tend to compromise between idle speed at a given stop-screw position and throttle response. And they can't die on snap-close throttle. Then I go ride it and check the very light throttle performance.

My experience may be a combination of slightly plugged idle circuits, altitude and fuel quality, though the local pumps say 92 octane non-ethanol premium. If I had a fuel hydrometer I could check fuel quality to a degree. I used to do that on every aviation-gas delivery. There was a spec for each of the two grades I hauled. The post-trip bucket-drainings went into my motorcycles and 320i BMW. They loved it but those days are gone these 15 years. I don't remember the Nortons being so finicky on av gas.
 
I ended up enriching them just a tad. Per above I had gone 1/4 turn more lean where the color just went into the blue. But going back 1/8 richer makes it just right. At the blue setting I noticed a lower RPM idle and a couple coughs when cold and cracking the throttle. Very fine adjustments. My cold start routine (well, Southern California isn't cold, but the engine's not hot) is to push down the Mikuni's enrichener. It fires for a second and dies. If I keep kicking with the enrichener on I can flood it. So after one kick, I turn off the enrichener and it fires right up, seems that little remaining fuel boost is enough. 2nd kick cold which is fine by me, I need the exercise. After warming up is so easy to start I can do it sitting down (low comp 7.5:1 helps) or standing on the right side, which sounds weird but not as strange as my 1951 BMW R51/2! I remember my '66 Bonneville with twin concentric and the tickle routine was a first kick every time after I learned the routine.

It's amazing how much helpful knowledge is on these forums.
 
You must log in or register to reply here.

Similar threads

D
Tuning the mikuni low speed fuel circuit with air screw
Replies
6
Views
235
acotrel
acotrel
D
Can you give me advice about tuning/jets etc on my single Mikuni VM34
2 3
Replies
47
Views
1,460
DennisMo
D
Whiterabbit
Very rich carbs on a 71.
Replies
17
Views
713
L.A.B.
L.A.B.
maylar
  • Locked
anybody here use a Colortune?
Replies
14
Views
1,506
acadian
acadian
Derek Wilson
  • Locked
Well, That Escalated Quickly...
2
Replies
26
Views
2,339
comnoz
comnoz
Back
Top