# Looking Inside the Cylinder While Adjusting a Carb



## Bob Driver (Nov 1, 2017)

Ever wish you could look inside the combustion chamber while adjusting a mixture screw on a carb? You're sitting there with a big V-twin barking in your ear and listening for the RPM to fall off... Wouldn't it be nice just to be able to look down inside the cylinder, while you're listening to Lynyrd Skynyrd on the I-pod, and say "Yep.. that looks about right". Well, you can... Ever hear of a *Gunson Colortune*? Motorcycle mechanics have used them for years to tune carbs, but they work just as well on lawn mower engines. It's basically a "see-through" spark plug that you can look inside at the combustion flame.

Remember High School chemistry when they were eventually forced to trust you with a Bunson Burner in spite of your past history? Same principal applies with the Colortune, adjust the fuel/air mixture until the flame turns the shade of BLUE you want (thus the name Colortune) . You can use them to set mixture adjustments, see the change jet sizing makes at various RPM's, or just stare inside your running engine like it's a plasma ball 

Neat little tool I use a lot. Downside is they're kind of expensive for a DIY guy, especially since they're sold by sparkplug thread size 10mm, 12mm, 14mm. They run $40-$50 on Amazon, or E-bay, but they can save you a hell of a lot of time if you're jetting a lot of race bikes.

Here's a link to a You Tube video from Gunson that involves a classic motorcycle that FredM will appreciate and shows you how they work. The guy in traffic control vest is just setting the low speed mixture, but you can do way more than that with them once you know how.





It must be way more dangerous to work in a shop overseas than here. We just had to wear steel-toed boots and safety glasses. It was a gentlemen's agreement not to come through the shop doors at 30MPH, so we didn't need the vest


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## FredM (Nov 18, 2015)

How do you know that Bob ??, damn hard to pick up the make, at the moment I am going for an older 350cc OHV AJS, there is a motif on the timing chain cover for the maggy, but I can't read this, the primary chain case looks AJ though, some researching coming up.

Those tuning plugs are a great idea.


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## Bob Driver (Nov 1, 2017)

I've paid attention to your post/profile. You're like me.... Any bike with the kickstand on the back tire is just plain cool no matter who made it.

The #1 thing on my bucket list is to make it to the Isle of Man for the TT. The Dunlop brothers and John McGuinness are some badass riders


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## FredM (Nov 18, 2015)

I was close, it is the AJS's brother, a 350cc Matchless, this one has been restored much better and I am not going for a year model, although the telescopic forks were around 1941.


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## FredM (Nov 18, 2015)

Bob Driver said:


> The #1 thing on my bucket list is to make it to the Isle of Man for the TT


The closest I have been to the Isle of Man races is a T shirt that a friend brought back for me many years ago and I still have this.


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## Bob Driver (Nov 1, 2017)

FredM said:


> View attachment 54915
> 
> I was close, it is the AJS's brother, a 350cc Matchless, this one has been restored much better and I am not going for a year model, although the telescopic forks were around 1941.


I was thinking a Matchless... Painted OD green and without the Big M, I wasn't sure


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## FredM (Nov 18, 2015)

Must be motorcycle day Bob, Cub has just posted in "what did you accomplish today" and his photo shows a board track racer in a store where he shops.

The motif on the timing cover in the video is Matchless now that I can see the photo I posted.


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## Bob Driver (Nov 1, 2017)

FredM said:


> Must be motorcycle day Bob, Cub has just posted in "what did you accomplish today" and his photo shows a board track racer in a store where he shops.
> 
> The motif on the timing cover in the video is Matchless now that I can see the photo I posted.


This is just 2 hours from me... I find it hard not to drool when I'm there. Supposedly the largest motorcycle collection in the world...


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## Denver (Mar 30, 2020)

I did only once” broke my nose, and blacked my eyes! I would like to see a clear engine working at 7 k rpm,s


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## Hoodoo Valley (Nov 14, 2006)

Ewwww indeed! There's a YouTube video I saw where someone used glass on the head of s mower engine then did high speed video of the engine running for some awesome slow motion of the explosions inside the combustion chamber.


Denver said:


> I did only once” broke my nose, and blacked my eyes! I would like to see a clear engine working at 7 k rpm,s


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## FredM (Nov 18, 2015)

Bob, they would have to hog tie me if I ever got there, I would want to be lifting a few bikes, especially a 6 cylinder Honda that was new early 80's, and a 650cc BSA Rocket or what we called the "big valve BSA", I was writing to a mate on Vancouver Island up until January last year and the poor coot got a brain tumour and Passed, and now I am writing to his son and he has been there and he sent me lots of info and how to do a virtual tour, a really great museum.


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## Bob Driver (Nov 1, 2017)

Yep... The museum is cool anytime, but I usually make the annual pilgrimage in early October during the Vintage Bike Festival on my 1977 GL1000. It's considered a "late model" when you show up at a place like that. That's when they break out the steam powered bikes and guys are riding around the grounds on stuff with Thor engines, or Ace 4-cylinders, like they were pit bikes.

The very best thing is that they open the track for AHRMA vintage racing. Nothing like watching a good race between some Indian and Harley side shifters, or the sound of a dozen early 20's board trackers hitting 100MPH down the back stretch.

Some guys want their ashes spread somewhere on an exotic beach, some guys talk about a 14,000' peak in Colorado as a final resting place. I told my wife just drop me in a big salt shaker and spend $15 to sneak me into the Barber Museum.


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## FredM (Nov 18, 2015)

And what better place to be Bob!!.


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## bontai Joe (Sep 16, 2003)

A co-worker's husband picked her up after work on his Enfield with a side car. I dreamed about that bike for a couple of years. Way back when I was a snot nosed teenager, My older cousin had a Norton 750 Commando, another bike I drooled over. But I never got around to buying a bike, and now I'm too gimpy to ride. But I still like to look.


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