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Lean cylinder, high EGT, beautiful pics!

Posted: Mon Apr 16, 2018 10:25 pm
by boeing7873
I bought a thermal camera and started playing with it to find the culprit to some stumbling on low RPM acceleration. Check these pics out!

Re: Lean cylinder, high EGT, beautiful pics!

Posted: Mon Apr 16, 2018 11:06 pm
by boeing7873
Another try at posting pics....

Re: Lean cylinder, high EGT, beautiful pics!

Posted: Mon Apr 16, 2018 11:08 pm
by boeing7873
A few more... Obviously something is wrong with my last cylinder...

Re: Lean cylinder, high EGT, beautiful pics!

Posted: Tue Apr 17, 2018 10:02 am
by pinzinator
Are the valves set correctly on cylinders 1 and 2? Is the front carb jetted the same as the rear?

Re: Lean cylinder, high EGT, beautiful pics!

Posted: Tue Apr 17, 2018 10:17 pm
by rmel
It will be hard to draw a conclusion from a Thermal imaging camera -- there's a fair amount
of error you can have versus the actual gas temperatures in the pipe. The only foolproof
measurement is with Pyrometers in the pipe and each at exact locations on the exhaust ports.

For accuracy measuring externally, your better off with a narrow beam IR gun with a Laser
spot -- and you want to get that spot exactly at the same place on each exhaust port. Your
imaging camera looks like it may support a spot beam? At that there's a number of things that
can throw the measurement off. The surface roughness of the metal, and if your headers are
treated with ceramic coating it's going to read very low and with variance -- I'm guessing that
is not your case though.

Even with Pyrometers in place, Temperatures at idle can show a significant variation from port to
port due to low flow rates, air mix and advance at idle. Try measuring the temperatures above idle,
at least up 2,000 to 2,500 RPM.

From my experience, idle temps are over 350C -- as measured in the tube. At load, chugging up a
steep grade for a period of time your going to be running about 650C on the coolest typically #1
and up to 800 on the hottest typically #3.

So you may or may not really have a problem here, but try higher RPM and see if things flatten
out a bit more -- and you should expect some variation between each port, up to 20% or so. Three's
air flow difference between these cylinders, also #2 and #3 have hot cylinders on both sides, then
there's the fuel flow differences etc etc.

Re: Lean cylinder, high EGT, beautiful pics!

Posted: Mon Apr 23, 2018 1:48 pm
by boeing7873
Excellent advice, will shoot the temps at 2000 RPM or more. Also, I took some new measurements with the camera and noticed the temperature readings vary with the angle from which they are shot. Getting closer to the pipes reduced the temp difference.
JC