Weber Balancing

[Duckpit]

I am currently running in my upgraded Zetec for which I have new 45's. I know how to balance one carb to another but I seem to have a difference on the individual barrels on one carburettor. Is there an adjustment on the carb to balance the barrels across a single carb/

 

thanks

[BlackSeven]

Sadly, its not uncommon with the newer Spanish built Weber's to have some imbalance between the left and right sides; one of mine is the same. Assuming they are the new 5 progression hole 45's they will have "idle bypass" circuitry and it should be possible to loosen the locking nut and open up the idle bypass slightly on the low barrel to balance airflow. It's not a perfect fix but easier than the other options of replacing the spindle, trying to twist the spindle or modifying the butterfly on the lower flowing side to balance within the carb.

Incidentally, what emulsion tubes are you using? A lot are supplied with F16's which in my experience left a slight gap in the progression phase no matter how rich you go on the idle jets. After a lot of research I have recently ended up with F4's which were recommended by someone else running a 2.0 Zetec and they are like a magic fix - I can now run sensible idle jets, (giving good emissions and economy) and have perfect progression with instant response at any RPM - F4's are not easy to find but well worth finding for a Zetec.

Rob

[Duckpit]

Thanks Rob

Yup they are Spanish & 5 hole progression, I will look at the emulsion tubes, but I have a 1.8 as I want to be in a particular class.

I bought them from Dunnell along with the upgrade

Nick

[Paul Deslandes]

The adjustment screws are usually 'hidden' underneath a little white plastic cap and there should be one for each choke.  Remove both caps on each carb, slacken the lock-nuts and gently ensure the screws are fully home.  Do not overtighten or you'll damage the screw tip, the seat, or both! 

Start with one carb first, then do the other.  Check the airflow for each choke of the first carb and balance by slowly undoing the screw of lower flow rate side. Re-tighten lock-nuts and replace white plastic caps. Do the same for carb 2 then balance the two carbs in the usual way.

You should end up with one screw on each carb fully home and the other slightly unscrewed sufficiently for balanced air flow.

Paul

[Duckpit]

Thanks Paul, now balanced (I hope ) and No 4 responding much better to tuning 

Rob - My tubes are F16, I havent pushed the engine yet but there is a bit of a pick up issue at low revs but once passed 2500 it flies but I haven't yet been above 5500 & rev limits at 7700. The head & pistons etc have been modified by Dunnell and I now have there hi spec cams, reputedly 210bhp

I have found a set of F4's so I will give them a go

I seem to have a problem with filters, the engine runs like a dog with the spongy socks, but once off it is fine, the K&N's dont quite fit the bonnet although they also work fine, currently running with gauze across each intake

Nick

[BlackSeven]

Nick, glad you managed to bring the airflow on no.4 using the idle bypass adjustment screw;  I presume you only needed to adjust one of the four idle bypass screws if you just had one carb with imbalance between its two chokes?

As regards air filters; I've had issues with the "sock" type on a crossflow; they proved very restrictive which may be why you are having issues. I have no experience of gauze filters on intakes but Dave Walker of Emerald writes a monthly piece in PPC magazine about setting up cars on his rolling road and he has recounted on more than one occasion that he has found gauze covers on the intake to also cost a lot of power.

Presumably you can't use K&N's as they no longer align with the bonnet cut-out now that you have the Zetec installed? The deepest K&N you can lay your hands on plus trumpets would however probably be the best option; maybe you could get the cut-out altered?

I hope the F4's help you out. Hesitation around 2,500 rpm  sounds like classic progression phase weakness and was exactly what I was having. You can improve with over-large idle jets but the best solution for me was F4's which bring the mains in earlier and fixed the problem completely.

Rob

[Duckpit]

Rob

The F4's made probably made the engine worse. What state of tune is your Zetec ?

I think I will go back to the F16's

Nick

[BlackSeven]

Hi Nick,

It's a 2.0 Blacktop that is standard other than the (5 progression hole) Weber's, Omex ignition only ECU and a 4-1 exhaust. 

Sounds like you may need some rolling road time to optimise the jetting for your modified 1.8 although some degree of low speed progression is probably inevitable when using modified cams with carbs.

Hopefully you'll be able to get your money back on the F4's via Ebay?

Rob