Thread: Tuning a carbie - Gas Analyser

providing you have the right version of the book you dont need it...

it will give you a basic setup to get the thing started and running and then it will tell you how to go about adjusting it while its running to get it all right....

then you can do a fine tune with the analyser

If youve got it running it usually only costs $30 or so to swing it past a place with an analyser and get the fine tune done.

The simple answer is no,
on a new car yes
but as the carbies get older the engine gets abit tired then the factory settings are just a starting point, to get the car ruining and idling so you can properly tune it.

You used to be able to get a thingy me bob that allowed you to see in the custombion chamber while the car was ruining that worked well you could set the mixture quite well

But nothing beats a gas analyser, I managed to pick up an old vane 2 gas one, have set the rangie up with this then checked the AFR with a Snap on MT25000 and it was spot on

T

The series would send the modern gas analyser Off the scale!
These were dirty engines as far as CO emissions were concerned, and if the engine is worn in any one of 3 areas,(Distributor, cam timing, compression) then you'll have no hope of satisfying the gas anyliser. Fuel mixtures at idle are easy to adjust, but if the carb has problems with the main or power circuits, then these will need attention also.

However, The old SU was a fantastic bit of gear, hardly any moving parts, no throttle pump or power valve, simplicity in action

The Suby will need a valve adjustment (If it is a OHV EA81 engine) to ensure proper running, and if it is a L series with the EA82 OHC cambelt driven engine, these have a more complex carb etc that could have vacuum leaks etc which will cause poor adjustability and running.

JC

also.......if you were expecting to see a nice grey tailpipe like the good ol days........
you can pretty much forget it.......unleaded will leave the tailpipe black......



all you need to set up a carby......is a vacuum guage......
then you tune the carby till you get maximum manifold vacuum at idle......

you want your engine to run at its best........
to set it via an exhaust gas analyser is pretty much only for passing an emissions test.....

running an engine a touch richer is always better for the engine.......
and that small amount of fuel charge that gets drawn into the combustion chamber
on each stroke.....is pretty much all that cools down the combustion chamber......

and also part of the reason why running an engine leaner can cause overheating.......which leads to detonation...........


just make sure you dont have black smoke coming out the exhaust.....

OK - so let's forget the analyser then!

Justin - It is an EA82 so no valve adjustments and lots of spaghetti attached to the carbie.

Tony - I remember them I think, you screwed them in in place of the spark plug or something.

I am not so worried about passing an emissions test, more just wanting to know how to get it to the leanest reasonable mixture, without being too lean of course.

So should I be going out and getting myself a vacuum gauge? I can see how this might be used at idle, but how do you fine tune the main mixture screw at running revs (say 3000RPM), or is this not critical?

Originally Posted by spudboy

OK - so let's forget the analyser then!

Justin - It is an EA82 so no valve adjustments and lots of spaghetti attached to the carbie.

Tony - I remember them I think, you screwed them in in place of the spark plug or something.

I am not so worried about passing an emissions test, more just wanting to know how to get it to the leanest reasonable mixture, without being too lean of course.

So should I be going out and getting myself a vacuum gauge? I can see how this might be used at idle, but how do you fine tune the main mixture screw at running revs (say 3000RPM), or is this not critical?

In the suby,Main running mixtures are set with the jet size. Some older carbs had adjustable main jets, and all SU type carbs are adjustable in this department by changing needle profiles, and a small amount of needle height adjustment is possible until it affects the idle mix.


The EA82 was a pain in the carb department with all the vac hoses etc, even the auto choke model was overly complex

If it has serious fuel economy issues, check the wear in the throttle shaft, it'll cause a lot of fuel to be drawn in on the overrun, causing enrichment on downhill and coasting = more fuel consumption.

JC

Originally Posted by DEFENDERZOOK

all you need to set up a carby......is a vacuum guage......
then you tune the carby till you get maximum manifold vacuum at idle......

Thanks for that info - didn't know about that. I've just done a lot of reading on this on the internet and have learnt a lot. Better get myself a vacuum gauge.......