Carburettor Tuning

[Farmerpug]

Ive got the 305 as ready as it can be for the MOT, all the things it previously failed on have been fixed, other problems and niggles have been sorted but im not sure about the emissions i cant really test them at home.

 

I see exhaust gas analysers coming up for sale on ebay, they all read C0, but not HC, would one be worth buying?

[Dead_E23]

Gunson's Colortune ftw; it's essentially a spark plug with a window in it. Works well enough and is quite interesting to use because you can see the colour of the flame changing as you fiddle with the mixture - if you can't get it to go dark blue it generally means your carb is full of gunge and needs pulling to bits on the kitchen table.

 

I've also got a Gunson Gastester. It works quite well, but isn't quite as much fun.

 

ETA: the HC test isn't very strict at all for older cars. There would have to be something pretty wrong with your engine before it failed.

[michael1703]

Pre August 86 registered cars are 4.5 CO and most cars will pass that*

[fordperv]

As already said a colortune would be spot on for you, if your m.o.t tester is friendly they may let you adjust your carb on the ramp

[jonny69]

CO and HC are going to be pretty much the same thing with a carburettor. Excess CO is present because of incomplete combustion due to rich mixture, so there will be HC (unburned fuel) present as well if it's running really rich.

[alf892]

Best just check timing first then lean it off till it hunts and then back a bit so it idles nicely.........should be close enough for an oldie

[steve_earwig]

if your m.o.t tester is friendly they may let you adjust your carb on the ramp

This. Although you've got more chance if you pick a quiet period.

 

Wind mixture screw in until maximum revs are achieved, then wind it back out 1/4 of a turn (well, it works on lawnmowers anyway...)

[lisbon_road]

Plenty of good advice there - especially the bit about doing it live at the MOT test which I always do.

 

I've often wondered if you could rig up a lambda sensor with heater on the end of the exhaust and run it with a voltmeter and see if the mixture is right - or are older cars always too rich to do that?  Might make a really accurate way of doing it though.

[spike60]

I think someone on here had made a DIY CO meter from a Lambda sensor, IIRC he posted in answer to when I asked about CO meters.

[spike60]

"I know nothing of the Gunson machines, probably a bit of a faff and for what they cost you could probably rig up a lambda probe in a metal tube with a bit of silicone hose to slip over your tailpipe to read with a voltmeter, and still have change for a couple of pies from Lidl."

 

From Des in answer to my CO meter question. I didn't try it, I bought a 2nd hand meter and now don't own a car it's any use for!

[fordperv]

The gunson gas tester isn't a bad bit of kit, I've had one for years, easy to use you connect your power, calibrate to 2.0% in air then shove your probe in the exhaust and adjust your carb to the desired figure, job done

[Farmerpug]

I Bought a sealey compression tester, The readings i got back from it do show some variance across the cylinders.

Quoting the PSI readings from each cylnder 160, 150, 180, 180. The car is not loosing any coolant or oil, and they are not getting mixed, its not overheating but the exhaust does have some white smoke coming out.