I would put the 45 back in, and adjust fuelling via the mixture screw.

Whats the ATV box then? Its fun messing with jets ain't it :-)

I would put the 45 back in, and adjust fuelling via the mixture screw.

Whats the ATV box then? Its fun messing with jets ain't it :-)

I tried adjusting the mixture, doesnt work, its way to far out of range with the Redline best lean idle adjustment to be 'right' in my opinion and still not smooth. I'm going for 50 now I think (dvdlerm has 50 if you notice). Its much, much smoother pulling away with the 55, and for that I would bear the initial flooding on start up and econ. loss.

the ATV (g40 box) is as it sounds :-D got one recently off another member. Just means you dont hit 2500 in second untill you get to like 32mph ha. Pretty sure I wouldnt need 3rd in a 0-60 (but then I supose many people dont use it with their shorter boxes.. ha)

That just goes to show you that no two engines, even similar specs require the same fueling. Mine was taken a few stages further than your spec and a 45 was slightly too big!!

Have you thought about a slightly bigger camshaft?

of course. GT would be the obvious next move I'm guessing as I'm running the ABD head on a facet pump.

I'm still not clear as to wether or not I will lose torque down at like 1500..? Thing is I really need a shedload of torque at around 2K cos thats where 5th is at 60mph. Also I'm a pretty gentle driver most of the time and dont often feel the need/ want to take her much past 2500.

also does the GT cam give a lumpier idle?, and if so by how much (bearing in mind I'm properly OCD ha!).

btw, might be of interest, I also gasket-matched my MH manifold (just thought it would be quite a rare thing..)

I doubt you would notice a decrease torque below 1500rpm, best thing you can do is try it and see how it feels!

That just goes to show you that no two engines, even similar specs require the same fueling. Mine was taken a few stages further than your spec and a 45 was slightly too big!!

This is what you try explaining to people that sell bike carbs and put "Jetted to suit GT" and it just doesnt sink in that the carbs would still need setting up again on the engine there being fitted too.

hmm. It would be good if I could get my colortune to work nicely.. Tried gapping it, perhaps it needs a different sealing ring, cos at idle its acts like a faulty HT lead and I'm not sure I want to trust it if thats the case.

I now have main jets of every size from 100-135 (plus the 150 LOL)

Also, I'll be pissing people off around here if I do get the colortune to work smoothly as I'll be having to hold the revs at like 5000rpm just to open the second choke haha!

Btw I've found the 50 idle jet is definately correct for my engine.

The correct setting is around two turns out and there is a definate 'range' of screw turns between revs dipping because its too lean and dipping because its too rich.. whereas before I could only get one or the other.

Just thought I'd update.

I've fitted a new Newman 264 camshaft and now playing with tuning again.

Just reading through peoples jetting again and I notice both Maxmax and Dvdlerm have larger primary air correctors than secondary.. whereas I started off the otherway around.

You have to remember, obviously the primary choke requires less fuel than the bigger secondary choke.

The "Air corrector" jet metre's air, not fuel. The bigger the "Air corrector", the leaner the mixture.

Thus, having a bigger "Air corrector" in the choke requiring less fuel is what you want, having it the other way round is false practice.

Also, bear in mind that the "Air corrector" works together with the main jet, a change in the main jet and the air jet needs to be looked at.

Are you doing it all by ear then? Looks like your doing well tbh, get it hooked up to a gas anaylser and see whats what!

yeh as far as the idle is concerned the 'best lean idle' method works 'by ear' and there definately is a very narrow sweet spot where the engine runs really smooth.

Something's bugging me though...

if the theory is 'use the largest air corrector combination available' (i.e. 210,185 or whatever) then richen your mains a little to suit... aren't we just calibrating our carb like we would for a 2 litre engine? And what would the owners of the 2 litre engine do to boost their performance if they already are using the largest air correctors as standard?

..Does this make any sense? Surely there is a 'correct' air calibration for the amount of suck your engine can generate? I thought a stoichiometric AFR was the way to go for performance with Nat.Asp. engines?

Plus I wish I had a gas analyser permanently in my car, it would make things so much easier! but I fear the faffing with welding a boss to the exhaust may upset my parents!

Never heard of that before to be honest, the first thing to get right on the main circuit is the main jet, then see what needs to be done to the "air corrector", not the other way round!

either one would lean/richen the mixture though?

Yes, but at different engine speeds, the air corrector only has a real influence above 4k!

oh rite, this I did not know..

would really like to learn more about the carb. I obviously haven't quite grasped it yet.

I switched back to the jets I got set up at the rolling road and it does pull better higher up the rev range.. I'm starting to see what the camshaft has allowed. But what I'm a bit miffed about is that 2000-2700ish is untouched really.. Was hoping for a significant increase there.

The igntion side of things may be hampering the perfomance now, maybe try sending the dizzy off to H&H Ignition solutions, they will be able to re-set the dizzy weights to allow for the new modifications etc, though it may not be much.

When i was using this carburettor, if i found somewhere that was a bit flat etc, i just changed the relavent jet(s) a few sizes up or down, if the problem worsened then you know you need to go the other way, and vice versa. Its all trial and error, spend a sunday swapping out the jets and different dizzy static timing settings, record everything on a spread sheet and log what the car pulled like on half and full throttle loads at each additional 1000rpm engine speeds.

yeh thats good advice, thanks. What I did was to retard the ignition timing a degree, seems to work best with the cam.

tbh its very smooth, and I'm definately noticing the difference now, though as I say seems not to have done anything down at 2K.

Every time I do these sort of mods I realise how gentle my driving style is/was and go a bit more revvy. Thing is, I used to think the gearing (in general) on these cars was exceptionally short.. but to be honest I'm now realising thats not the case. I mean my ATV box is really long, but the AAU 4 speed I had wasnt terrible. I was getting a lift in a mates Renault Clio 1.2 the other day and looked at the tach at 40mph reading 2K and said 'why not go into 5th'.. then he told me he already was! ha. My G40 4th does 1750 at that speed!!!

You have to remember, obviously the primary choke requires less fuel than the bigger secondary choke.

The "Air corrector" jet metre's air, not fuel. The bigger the "Air corrector", the leaner the mixture.

Thus, having a bigger "Air corrector" in the choke requiring less fuel is what you want, having it the other way round is false practice.

hmm, well as I say I got it set up at a RR and he got it as 155, 185. Thats what I'm currently using. I swapped them round and straight away and it felt very flat.. So I don't know wether that's just my engine being weird but..

Also I only tested it under 2K and straight away I just thought.. this won't do.. So at least on my carb the air corrector is having a very significant influence down low.

plus the 'less fuel' is dealt with by the smaller primary jet?

Engine code/capacity : GK / 1272

(I think it says 1263 cm3 on the Zulassungsbrief)

Tuning modifications: Raceland 4 branch exhaust manifold, 3F centre box, custom rear box, K&N top mount pancake filter, Huco suction pump, Bosch W5DC plugs, Hotwires leads, Flamethrower coil.

Carburettor: Weber DMTL with 24mm/25mm venturi's, swirl pot, on 5cm high Bakelite spacer.

Jet set-up:

IDLE: 50 70

MAIN: xxx 127

(Was 125 primary main, now 112.5)

EMULSION TUBE: F33 F33

AIR : 185 220

PUMP JET : 40

Edited 16 July, 201214 yr by dvderlm

You have to remember, obviously the primary choke requires less fuel than the bigger secondary choke.

The "Air corrector" jet metre's air, not fuel. The bigger the "Air corrector", the leaner the mixture.

Thus, having a bigger "Air corrector" in the choke requiring less fuel is what you want, having it the other way round is false practice.

No, I think it depends...

Not sure what on, tribology and fluid dynamics I suppose.

Maker's settings:

Ford Cortina GT 1500cc Weber 28/36 DCD

50/140/F30/230

70/155/F30/180

Peugeot 403 1500cc Weber 28/36 DCD

55/125/F13/200

55/130/F13/220

Not forgetting Lancia Beta coupe 1.3 (more powerful than the 78bhp Cortina GT with 84bhp)

with a 22/22 32 DATR 3/250 Weber

50/110/F??/190

70/115/F??/260

Edited 12 July, 201214 yr by dvderlm

Engine code/capacity : GK / 1272

(I think it says 1263 cm3 on the Zulassungsbrief)

Tuning modifications: Raceland 4 branch exhaust manifold, 3F centre box, custom rear box, K&N top mount pancake filter, Huco suction pump, Bosch W5DC plugs, Hotwires leads, Flamethrower coil.

Carburettor: Weber DMTL with 24mm/25mm venturi's, swirl pot, on 5cm high Bakelite spacer.

Jet set-up:

IDLE: 50 70

MAIN: 125 127

EMULSION TUBE: F33 F33

AIR : 185 220

PUMP JET : 40

Have you now got good colour spark plugs? I've tried a range of jet sizes, I did think the 125 primary felt good.. but fuel econ?