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MG MGB Technical - Exaust Gas Analyzer (sp?)

I saw Moss has a Exaust Gas Analyzer for $200 do any of you know if they are any good? The part number is 386-220. I can't tell by the picture who makes it. I would like to see an owners book or hear some first hand experience before I spend $200 on a pig in a poke.
Joe Taylor

Joe. This is probably the gunson's CO meter. A true "exhaust gas analyzer" normally measures several different things--CO, HC, NO, CO2, etc. The professional grade machines cost several thousands of dollars. Most have to be calibrated using some form of bottled test gas or other test device. The Gunson's CO meter measures only the CO output of the car and its "test standard" is simply warming the meter up and setting the scale to read 2.0% in ambient air. Gunson's claims that, when the meter is set in this manner, the meter will accurately reflect the tailpipe CO emissions. I have not found anyone who has been able to set their car with a Gunson's CO meter, then drive to the emissions testing station and get a test reading that resembles the Gunson's reading in any way. Most commonly, the Gunson's reading will be much higher than the test inspection station's reading. Sometimes, to the point were the CO is so low that the HC skyrockets and you have to re-adjust the carbs. This leads me to question the ability of the Gunson's CO meter as an engine tune up tool. For emissions work, it is all most of us can afford and does provide some form of measuring device which may be used when adjusting the carb(s). Les
Les Bengtson

I've succesfully passed emissions with both my RB
midget and MGB using the Gunson's.

However, I know it is not especially accurate. My
first Gastester went way out of adjustment after
four or five uses. It read much higher than the
actual CO, hence I ended up setting the carb too
lean.

My second gastester seems to be working much better.
I get consistent readings when re-checking the
mixture every few months.

Be careful not to rev the engine with the gastester
connected, and let it sit for a while after
disconnecting the power.
Ronald

Also, check www.lbcarco.com for good prices on
the Gastester -- they seem to import many Gunson's
items directly at lower cost. (No financial interest,
just a customer.)
Ronald

Joe,

I bought the earlier version of this device from Moss, about 6-7 years ago, specifically to help my '67B pass California smog test. I can't tell you that the readings will match one-for-one with the test printout, because I don't recall comparing the numbers. However, I will tell you that I got better results than any other method I've ever tried. Using this tool, I was able to lean the carbs down to just the right setting, without going too far. And it's the only tune-up method I've used that I could count on for repeatable, predictable results. I am also more confident than ever that my mixtures are balanced.

A caveat though: this tool is a bit fiddly to use. In my experience, you have to be anal about calibrating and keeping as many things constant as you can. And I found that I had to move fast, before the calibration shifted, or the thing filled up with water (condensed exhaust vapor). The measurement tends to creep over time, so if you're too slow, you won't know whether it's the device moving or your mixture is.

If you're going to have to pass smog every year, and you prefer to do your own work, or you like these kind of toys (like me) I'd recommend it. Otherwise no. In my case, they did away with the smog test, so after the last check and after resetting the carbs for peak power, I haven't needed to touch them. I haven't used the tool for 4-5 years.
Terrence Goodell

Gunsons make two models - the Digital and the Professional at nearly twice the price, around UKP80 and UKP150 respectively. For the extra cost of the Professional you don't seem to get any more than from an auto multi-meter which is a bit easier to carry around! I have the Gunsons and find it has become consistently pessimistic by about 2%, but at least it *is* consistent so I can compensate when checking before the annual test.
Paul Hunt

I purchased the Gunsons professional model last year from JC Whitney. It was a great help in getting my car to pass Colorado emissions. Here is my take on the readings; If you calibrate the tester to 2.0 at ambient air then insert the probe into your tail pipe and it now reads 3.5 then you are emitting a concentraion of 1.5 % CO (3.5-2.0). That is assuming that the ambient air that you are reading is free from carbon monoxide. So if you set it at 2.0 ambient air and you then get a reading of 2.0 while measuring your exhaust, then your exhaust is just as free from carbon monoxide as the ambient air was.
This is just my take on it.
John
John F

I recently bought a brand new Gunson Gas Analyzer and I've never used it, as here in New Orleans emission tuning is not the issue. I set up the SUs on my MGA perfectly going through the factory procedure. If anyone is interested in purchasing it (brand new) I'll give you a good price.
-M.S.
Martin Straka

This thread was discussed between 16/10/2002 and 20/10/2002

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