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MG MGB Technical - Gunson Exhaust Gas Analyzer

Have any of you had any experience with the gunson exhaust analyzer? I'm considering picking one up to make carb tuning a bit simpler. I'm currently running a Weber downdraft but may switch to SU HIFs.

I'd be curious to hear any feedback about the Gunson.

Thanks!
Steve Lipofsky

It works, I've passed smog using it. However,
it has a limited lifespan, two of mine didn't
last longer than a year.

Gunson's has a repair service in the UK, but
it doesn't seem possible to get it repaired in the
U.S.
Ronald

Mine is regularly pessimistic by about 2%. Before each annual test I set the carbs to just below the limit, then get a printout back from the test which more than 2% better than it needs to be, then adjust them back on the Gunsons to the limit+2%. If you see what I mean.

It doesn't help with carb tuning on twin SUs, you still have to use something like the Gunsons Carbalancer and the lifting pin and Mk I ear. Once you have twin carbs balanced for volume and mixture you then use the exhaust analiser to achieve the required tailpipe emissions, if required, by adjusting both carbs by *the same amount and in the same direction*.
Paul Hunt

Thanks!
I realize that I'll still have to balance the carbs and my BGT doesn't need to pass emissions here in Mass. I thought the Gunson might be useful for adjusting idle mixture on the Weber and/or SUs, jets on the SUs, and help with proper jet selection on the Weber as well.
Steve Lipofsky

Steve. My experience is similar to the above. You calibrate the meter in ambient air so that it shows 2%. This is supposed to be a reference standard, unrelated to the amount of actual CO in the air, but I am not sure I believe it. Like Paul, I find the readings on my machine to differ significantly from those of the emissions inspection station, with the Gunson meter showing higher than the station test equipment. But, the use of the meter does introduce some element of repeatable tuning as opposed to the "by guess and by gosh" form of tuning by ear. As Ron notes, the meters are somewhat fragile. My first one lasted about three years before it became useless. (It reads in negative numbers between -5 and -13.) E-mails to Gunson's have produced no reply, so their level of customer support cannot be considered good. When working properly, the CO meter makes tuning much easier. Better yet would be a mixture analyzer reading out fuel/air mixture. These used to be available, but, with the emphasis on emissions rather than performance over the last 25 years, I have not seen any being sold. Les
Les Bengtson

Steve,
Last fall I was looking at the same unit, as I wanted something to help in the tuning process. The one problem that I noticed about the Gunson was that it might be very helpful to set up the mixture at idle, but since it wasn't mobile, it would not help when the car was actually being driven under load, which funny enough is where I spend 95% of my MGB time (when my car is actually running...). Since I wanted something to measure my mixture while cruising, part throttle, full throttle, going up and down hills, etc. I had to look elsewhere. I'd seen comments on this BBS and elsewhere suggesting that an air/fuel ratio meter might be the ticket, since it can be temporarily/permanently mounted in the car, and thus you can see if your mixture is correct in all types of driving conditions. I have a couple of different needles for my SU's, and I wanted to know which one met my needs best. Short of spending many hours & dollars on a dynomometer, this seemed like the best alternative. I ended up buying an Edelbrock kit from Summit Racing. You will need to have a bung welded into the manifold/header, as close to the collector as possible where the exhaust is the hottest. The oxygen sensor screws in there, and is connected to the monitor which is in the car. Now I'd like to tell you how wonderful this setup works, but I'm still waiting to get my reconditioned head back on the car, and then I'll find out if my logic was correct.
Theoretically this sounds like the ultimate way of setting the carbs up, short of finding a dyno. Once I have mine set up as best as I can, I'll take it to the local British shop that has a dyno, and see if I'm anywhere close. Summit has a couple of different air/fuel ratio monitors in their catalogue running around $125.00 US. Hope this helps.
SteveO

I bought one of these three years ago.

Love it.

Buy the Gunson see-through sparkplug and use it as well, makes tuning the twin SUs even easier.

I got it spot on using the both of them, makes the engine nice and smooth through the revs.

Erik.
Erik

This thread was discussed on 11/01/2002

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