%age Carbon Monoxide - Gunsons Gastester

B

Brian-Northampton

Administrator
All,

While tuning up my P6 (2000 TC 1971) I put the Gunsons Gastester probe up the exhaust (all according to the instructions). My reading was 8% - I think this is high and would be interested in other forum members to pitch in with their values - if they've done the test.

I understand that the MOT requires 4.5% for cars built post 1975 (and a visual only prior to this) but I don't know if Rover made any emission modifications prior to '75

I believe that I'm tuned correctly, as I used both the colourtune and the carb lifting pin to confirm the correct mixture. My timing is correct at 6deg BTDC (running leaded fuel)

My carbs/dizzy have all been overhauled in the last few years, she's been reshimmed and I have good compression on all cylinders (>190psi)

BTW - I have the HS8 carbies

Cheers,
Bri.
 
I have one of these testers and have found it to be quite accurate if calibrated correctly. I always found the colourtune to be a bit hit and miss, and certainly didn't help with the MOTs.

8% is quite high, I used to be able to get my 2.2TC to run about 3% easily, you should certainly be able to get it down to the 4.5% Post 75 MOT limit.

Usually you can just wind the jets in a little to acheive this and you'll probably find it runs a little smoother too. (not to mention saving you a bit of petrol) Make sure you do both evenly 1/4 turn at a time and give it a little rev up and allow it to settle between adjustments and checking the meter.

Obviously make sure everything else is ok first (air filter, timing, spark plugs etc) and make sure the choke is fully off. Plus make sure the carbs are ballanced properly, as one can be running lean but the other rich.
 
Interesting Richard thanks.

I must say that I found her to be a complete dog trying to tune with just the Colortune kit - hence I also use the lifting pin.
The front carb would give me a lovely bunsun blue and the lifting pin reacted accordingly.
The rear carb always looked to orange (indicating Rich) and when I tried to turn down to get a blue, the lifting pin wanted to stall showing a weak mixture.... in the end I kept increasing the mixture and until the lifting pin decided that I was right!

Maybe at the weekend I'll follow your recommendation and stick the GasTester on, double check with the lifting pin that I think I'm balanced (I'm confident about the throttles), and then turn down the mixture screws a flat at a time (or maybe a quarter depending on sensitivity) until I get to 4.5% and then see how she runs ............. I'm not feeling that confident though but lets see!

Cheers,
Bri.
 
You really need a flow meter to check the balance, the wonderful people at Gunsons do one of those too, carbalancer or something like that, I've got one. Or of course you can use the "bit of pipe" method and listen to the hissing.
 
Hi Richard,

Yes, I've got a CarBalancer - great piece of kit when you can get it to work. Trick is trying to get a good seal round the venturi without fouling the air cleaner studs. This photo shows how I acheived this with a small Christmas pudding bowl, stanley knife, bostik, kitchen sealant and draught excluder.

Dogs danglies - works beautifully!

Bri.
carbtune.jpg
 
On the V8 my Carbalancer fits easily on the carbs. Does removing the flange on the end of your carbs make it any easier?

Before worrying about the emmisions too much , give the carbs a good clean and check how deep each jet is set below the bridge . If the carbs aren't both the same , then you have problems with the jets/needle/floats and the carbs need an overhaul before going any further

Also check the needles are both set to the same depth in the body of the piston
 
I have both the Colourtune and the CO Meter.
In order for my car to pass the emissions test I moved the timing as close to TDC as I could get, and leaned each carb. I had the emissions report from the testing station and compared the official test with my CO Meter. I learned what numbers I needed to pass the test using my meter.

The car barely ran to the testing station.

After the test, I made the car run more smoothly. The end result was that the car idled better and had less emissions.

Eric
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smilie
 
Your right, I do need to give them a bit of an thorough checking over - I'm thinking about making this a winter job and get the inlet manifold off the car and check them over on the bench - there's very little room in the engine bay to set and check jets.

On a slightly different note, and I'd value the forum's opinion on this one. To tune the mixture on the TC, I've got 2 Gunsons Colortunes. When I last did them, I used Cyl 2 and 4. What does the forum think about which to choose. Obviously choosing the 1,2 and 3,4 banks of cyls but will you get the same results for 1&4, 1&3 etc.

The reason for me asking this question regards my earlier comment where I couldn't get a bunsun blue on the rear carb (cyl 4), when I did get close to blue, the mixture was way too weak.

Cheers,
Bri.
 
I don't know which carb feeds which cylinders on a 4 cylinder Presumably they are paired 1+2 , 3+4 . As long as you test one cylinder fed by each carb , you should be OK

Might be worth swappiing over the Colortunes to see if they both show weak on no. 4 cylinder

Are there any vacuum take offs on no. 4 ? EG the servo , breather etc .If one was laeking that could cause your problem

Does no. 4 spark plug come out looking as if it's been burning weak ?
 
Don't forget there is a balance tube across the inlet manifold (where the servo vacuum is taken off) this will have an effect on the overall isolation of the two carbs.

P.s. that's a diferent setup to the one on my old 2.2tc, mine just had a large air filter box which meant you didn't have those two carb extensions (the bit you've put the christmas pud tub on ).

I spent ages trying to get mine to run straight, rebuilt the carbs with new needles and jets etc, balanced on and off the car, several times, and they were never quite right, I suspected either the pistons were badly worn or the bimetalic temperature compensators in the floats were dodgy, it was ok once fully warm but terrible when cold. I gave up in the end. Would have been much easier with a single carb !!
 
Thanks for your replies everyone. I think that I've probably got a slight problem with one/both of them and so I've put them on the list of Winter jobs - first time for me to dismantle them, so I need plenty of time - It's Knebworth Car Show on August Bank Holi weekend, and I don't want to jeopardise that one, so it'll be after that.

Look out for my cries of joy or help over winter depending on whether I've managed to get them back together or not!!!

Cheers,
Bri.
 
Just a quick update on this one.

I've had the carbs off (and discussed on other posts) but the cause of all my problems was the inlet manifold gasket. When I took them off, the old paper was soaking wet - no wonder the rear carb was way out and always reading rich on the colour tune. I had to tune it with so much fuel just to idle with all that water going in! %CO is now very good!

Morale of the story? As stated so many times on this forum - careful about trusting a garage to do work. Your best checking them afterwards. My garage obviously didn't tighten the manifold down enough. My guess is, they couldn't work out how to tighten those middle two nuts - where you have to get your socket set through the inlet manifold to reach them!

All fixed now - now other idling problems.......... but when I've had a look this weekend, I might be asking about potential air leaks from the servo - And no, it's not the carb 'O' rings ;-)

Cheers,
Brian.
 
I didn't get to see that carb tool adapter the first time through the posting. I love it!! I'm going to make myself a similar adapter. Last time out I used those silly SU kit rods that you put in the dashpots.
 
I've seen those rods on an MG website. I thought the theory sounded good, is your experience different?

I still find using the carbalancer difficult to be accurate, it's not an easy tool and needs alot of shaking to stop the peg sticking. Perhaps using both carbalancer and rods would give a very good result indeed.

Glad you like my home made tool - necessity being the mother of invention! (and a love for Christmas Pudding!) The size of the bowl in this case was ½ pint. That would be half a British pint!

Brian
 
I used to have a "Unisyn" balancer which worked well on the Jag,but that tool has disappeared. I have a "Synchrometer" which just fits in the space between the firewall and carbs, but then you can't read it. But your plastic bowl convertor will solve this, I think.

As the metal rod kit measures the height of the carb pistons, I'm not sure it takes into consideration vacuum leaks or other carb mechanical differences which affect actual intake.
 
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