Weber tuning

[stevemersey]

My son and I have made great progress with the 1991 Zetec engined 7 on twin 40's we bought at Christmas, and it runs and drives pretty well now, but we can't help looking for more.

 

We just had it hub dyno'd at a very helpful outfit in Birkenhead, Auto Sport North, and got some reassuring numbers for peak power, but at lower revs the fuelling was very rich and the torque curve all over the place. Long term we may well go to fuel injection but for the moment we want to extract the best from what we have. Oh and our fuel consumption is awful.

 

So two questions, is it possible to get good fuelling across the whole rev range with Webers or am I being too ambitious?

 

And, following on, if we should be able to get things better than they are, can anyone recommend someone to look at it who is based here in the North West?

 

 

[Andrew Walker]

I had an 1800 Zetec on twin 40s and would get 30mpg on the usual road driving.

 

What engine management are you using and does it include a throttle potentiometer?

 

 

[Roger King]

A well set up pair of Webers will drive near as dammit as well as a well set up injection system. The problem is that most aren't and many assume that that's what they're meant to be like.

 

There's no magic to this, just experience. I'd like to ask what the dyno did if they didn't sort this out? To be honest, getting the big numbers is relatively easy, it's the driveability that takes real skill.

 

To give an example, it's perfectly possible to build Crossflows with a 264 (full race) cam that will happily poodle around a multi-story car park looking for a space.

 

You won't get the fuel consumption as good as properly set up injection, but fitting 3d mapping will generally improve matters by about 20%; if you're already too rich on part throttle a proper set-up will also make a big difference. 3D will also make a big difference to part throttle torque and make the engine subjectively feel bigger, even though peak power figs will be the same.

[stevemersey]

Roger,

thanks for the comments. The dyno session was short and cheap for us to get a baseline, they made it clear they could not help with webers, and the runs were for our information only so I have no complaint. They were very helpful and seemed to be pretty experienced at working with injection if we need them in the future.

 

I am encouraged by your information though, and will put some effort into improving the set up we have. The car is pretty drivable, I can pootle in traffic quite happily, but it just does not feel as torquey as I might expect. And the fuel consumption and plugs demonstrate that we are way too rich.

 

Andrew,

30mpg sounds a good target to aim for then. We have a gems engine management system that seems to predate any I can see on their website and yes we do have a throttle potentiometer. I am only just looking at the engine management for the first time and will do some further research.

 

 

[Roger King]

Yes, that's fair enough if they made the situation clear, and it is getting harder to find genuinely experienced Weber technicians.

[Klunk]

Hi Steve ,

 

Is it a 1.8 or 2.0 litre? Any modifications to the cams etc? Can you post what size chokes/emulsion tubes/mains/idles/pumps you have in?

 

Regards,

 

Giles

 

 

[stevemersey]

High Klunk,

 

It is a 1.8. The previous owner did not have a lot information on the engine. It has visible Raceline external parts and a lightened flywheel and what were described as Kent Cams but no model number. I suspect the head is unmodified.

 

Peak power was given as 125 at the rear wheels at 6500 on the hub dyno. It feels "cammy" but very drivable at low revs.

 

Chokes are 34mm

The main jets are 135

Emulsion tubes F16

Idles F8 60

 

I am suspicious that 60 seems large for the idle jet, and the air bleed similarly rich, yet I can get a very smooth idle at 1000rpm or less at about 1 1/2 turns out on the idle mixture screws.

 

All advice welcome.

 

 

[Klunk]

Steve,

 

Sounds like you probably have a 130ps engine with 2 litre cams (~150bhp at flywheel) assuming no headwork. Are cam verniers fitted? What air jets are you running?

 

34mm chokes are fine. Often people try and run 40's with 36mm chokes which, whilst giving a little bit more bhp at peak revs, normally leads to a loss of midrange torque and increased fuel consumption due to poor fuel atomisation.

 

My past zetecs have all been rich on idle so the idle may be okay - I will have a look through some of my old settings and report back.

 

Regards,

 

Giles

 

 

[Eugene]

Eugene is a 210 BHP 2L Zetec.

I get well over 200 miles to a tank, so as a 7L tank that's above 30MPG.

And it is very drivable - no issues at all.

 

But, I have 5 hole progression Webers (45s).

This made a big difference!

Before that I had to run rich to overcome the fulling issue at low revs, especially during the progression stage (obviously).

 

There is a Dropbox account with a load of Omex maps in for Zetecs if that helps?

 

[stevemersey]

Eugene,

thank you for that. These tales of 30 mpg give me hope.

[Klunk]

Steve,

 

Sods law, I can't find my old 1800 settings. However, by way of comparison my 2.1 litre (no, that's not a typo ) Zetec has mild porting with newman 270 cams and dcoe 40's. This was set up on an engine dyno with the following settings

 

Chokes = 34mm

Emulsions = F11

Main = 115

Airs = 150

Idles = 50F9

Pumps = 40

 

Idle screws are 2 1/4 turns out and the carbs are type 151 with 3 progression holes.

 

Looking at the figures it looks way too lean but this setup has run perfectly for 10,000 miles and easily passes the pre 95 emissions checks and returns 28 mpg with a 5spd box and 3.92 diff. I got 35mpg by changing the diff to 3.14 for a european tour!

 

I agree with Eugene that 5 holes carbs are better but these are really only necessary for 45s on a 2 litre zetec. I have never had a problem with hesitation on progression with 40s with 3 progression holes on either a 1.8 or 2.0 litre engine

 

Obviously there are many variables and a dyno would be best, however you could try some 50F9 or 55F8 idles as a first step if it's rich on idle.

 

On another tack, is the throttle pot adjusted correctly?

 

If you can make it to North Shropshire you're welcome to try what I've got lying around before you go to the expense of new jets etc.

 

Regards,

 

Giles

[stevemersey]

Giles,

Thank you for the offer. Those are interesting looking specifications and will give me something to mull over.

 

 

[millsn]

With the zetec it is a progression (holes) issue which is why so many people originally running carbs are now on tbs.

[Eugene]

Already been said...

 

If it helps, my carbs setup is:

 

45 Webers

 

Idle: 50f9

Main: 140

Air: 155

Pump: 45

Spill: 40

Choke: 36

Emulsion: f16

 

As said, I get great economy, and good pickup.

 

😬 😬 😬

[zetec]

Oh yes! As its a zetec thread Can i join in???

 

Carb tuning/ 100% northampton motorsport.

 

My latest tune & r/r set up was done "in house" by webers ( the very man that set up the JPE's)

As Eugene said above mine is running slightly rich with large mains to overcome issues with progression flat spots.

 

Mine runs fine if a bit rich, well mine used more fuel than an r400