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Interesting Carb Tuning with Colortune article

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jsneddon

jsneddon

Jedi Knight
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NFI and all that blah blah blah.

I was reading Allan's post about valve sizes and did a quick google on David Vizard.

He has a rather interesting method of getting the optimum mixture on carbs with using the Colortune (for those of you not familiar it is a spark plug with a glass window so you can actually see the color of the spark).

The article is here:
https://www.niksula.hut.fi/~mdobruck/siililand/mini/diy/10/dyno.htm

he jacks the car up in the rear and with a buddy running in 3rd gear at WOT he has them drag the brakes until the revs drop to 2000 and looks at the spark color. Very interesting in-depth article.

Do please be careful out there though... jeez... one slip of the jack stands and something or somebody is toast.

/ubbthreads/images/graemlins/nonono.gif
 
I like it!

I'd take the rear wheels off the car, just to be sure, though.
My car has an S&S "Harley" carb with an adjustable main jet (like an old lawn mower). I keep thinking I should have a dash mounted knob to turn it...that would be even better.
 
Reminds me of the day at a Ferrari shop when it was time to fine tune the Daytona prototype that was being restored. The master pulled the exhaust headers back a bit and had me hold the throttle at 6,000, while he twisted about until a pretty blue flame came from each port. What a sound.
 
Has anybody used an O2 sensor with an Air Fuel Ratio gauge to set the carbs?? I have a Westach analog A/F gauge on my supercharged Miata that has proved to be very valuble on two occasions when it showed lean conditions when in boost. Since it has a buffered needle, I can see at any given moment how the air/fuel ratio looks. I believe I read an article awhile ago where someone with years of experience tuning LBCs thought that a certain car in question was running too lean. An O2 sensor was installed and discovered that the A/F ratio was too rich. The old mechanic thought it was poppycock, but they leaned out the carbs just for the heck of it. Well, the son-a-bi*** ran like a raped ape. Sometimes new technology can be applied to the old stuff with good results.
 
I had one of those Colortune plugs 35 years ago in the UK.
They were a new idea then and worked well, but I always had an uneasy feeling when leaning close over it peering at the flame colour. I couldn't help thinking that it was just a piece of glass between me and a lot of hot gas pressure, always had the idea that it was a rocket waiting to go off in my face. /ubbthreads/images/graemlins/cryin.gif
They used to have a warning not to exceed 3000 RPM.
 
I like the idea of testing with a load and seeing how the mixture burns on the way up to max power. The safety with the car running max-out on jack stands is a concern and with the modern equipment of today, it seems some one could rig up a digital camera to record it or with the fiber optics see it real time while inside the car. Alta, do you think the mfg ever thought of having a full load on the window?
 
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