years ago i brought a gunsons gas tester mk2..its the yellow one with a needle (no digital readout)
i never used it and kinda expect it to be none too accurate
has anyone used one and found it any good? with proof from a calibrated tester?
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I have but to be honest with all the cars now needing cat tests the old analogue is not accurate enough for this but if you work with pre 93 cars of any type then so long as you follow the warmup period and make sure the pickup pipe is clear then it is 100% accurate if a little slow to show the true result if accelerator is blipped.
The later digital one is even better and i have one at work.At the side of my proper machine the results are excellant and can certainly help you get a cat equipped car through the mot,and you can use them outside powered off the car battery.
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\"a little man in a big world/\"
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all my cars are older than 93
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Yes, I have a green one with the digital display. I used to use it on the BX 16v.
Before the MOT, (pass level below 3.5%) I used to set the mixture at about 2 to 2 1/2% The official test figure was always 1/2% above the Gunson setting. (Used to richen it up after, it ran smoother!)
I found that it payed to let it warm and settle, adjusting as necessary, for as long as possible. (used to connect it to a doner car,adjust until it seemed to be stable and go and warm the BX up in an Italian fashion, come back and check it.
It also pays to adjust mixture as required, rev engine to clear it, then let reading settle again.
I don't use it on the Xantia or MX5, but I may be able to use it on the MR2.
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I've got the digital one & it's great. Just used on the Porsche which failed at 5% CO and wouldn't adjust. Now showing at 1.8% after an AFM change and will get booked back in for MOT next week!
Funny how many of my mates borrow it as well!
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The old Gunsons, mk1 & 2, actually used to measure CO2 and by calibration to the CO2 in normal air would give an approximation of the CO in the exhaust gas. This method is barely more accurate than the previous diy method of looking at the exhaust pipe, black = rich, white = weak. A museum might be interested in aquiring it! Actually I've also got a Mk2 at the back of the garage but it hasn't been used for 20 years.
The later Gunsons, with digital display, actually measure CO so they can be useful.
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A good idea is to run the tester from a spare fully charged battery. This avoids any voltage variations when running the tested car engine at different speeds.
The tester is also sensitive to movement so try to set it it up in ts final postion when setting the the initial 2% figure.
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pmh (was peter)
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I used one for years and years on a MkII Golf. The reading on the analogue dial would drift over a period of a minute or two by about 0.5%, but the average was bang on compared to the readings I sometimes got from MOT stations. In 18 years the car never failed on emissions. Much, much better than looking at the exhaust pipe.
A thorough warm up of both car and meter is essential, and as someone said, don't move the meter around once it's calibrated.
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Not particularly accurate but at least it gives you an indication that you're turning your CO up or down and that you are not way over the limit.
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