I've had my weber on my mk2 for a couple of weeks now and the fuel consumption has nearly doubled since i changed from pierberg.I'm pretty much getting 115 miles to £20

also i am suffering from spluttering when i get up the revs but this only happens now and again.itys also nearly impossible to drive when flat cold even with the choke on but when it wams up slightly its fine.

when i accelaorate i can smel fuel too.

I'm pretty new to carbs and i dont know wich jets are for what.when i got the carb it was on a mk2 that i broke for spares and i pretty much just bolted it onto mine when i swapped the engine(not what the carb came from)

the engine is a mk3gt bottom end with mk2 1.3 head,and slightly ported and polished inlet.

Edited 9 May, 200917 yr by herrod

Sounds like you need to lean the carb out,sort idle and choke adjustment idle. Also clean jets and establish what jets you have. I'm no expert, Steveo3002 and dvderlm on here will no doubt give better info.

Also check both the weber threads in the F.A.Q's above which have pretty much all there is to know. Also here's a few good threads that will help:-

http://www.clubpolo.co.uk/forum/index.php?...922&hl=jets

http://www.clubpolo.co.uk/forum/index.php?...c=94138&hl=

http://www.clubpolo.co.uk/forum/index.php?...=110518&hl=

cool cheers.ill have a good look at the jets later and come back with what I've got

the jets i have are 95 main and 120 secondary main

i have a weber filter on there could this be causing the ridiculous fuel consumption?

what is the best thing to do with the vacume pipe that comes from the box on the bulkhead?

cheers ross

i have also had a play with the mixture screw and it dosent realy make a difference to the fuel consumption but dose run better 2.5-3 turns out

MIxture screw is for idle only, the mixture during driving is metered by the fixed fuel jetting and their respective air jets, hence why you haven't really noticed much change in the fuel consumption.

Although if your mixture screw is near the end of the thread, either in or out, it is wrong. Generally if its too far out it means the idle jet is too big

Edited 28 April, 200917 yr by RedRoller

sounds like it's not jetted quite right, what are the rest of the jets?

primary secondary

155 185

f22 f30

95 120

If it was previously on a Mk2 Polo the jetting surely can't be that far out...

but 95 is a tiny bit mean for primary main (maybe it's tuned for economy - would be sweet if it was paired with a rich-tending emulsion

tube like an F24 or F33), and 120 is a bit generous for secondary main, but you say you've got some head porting..

It's fairly close to the stock Weber, and wiith a more free flowing filter probably okay. K&N say go up 5 om main jet sizes for example.

The other parts emulsion/air of F22/155 and F30/185 look fine.

What size are the idles? I'd expect 45 and 70.

Now then:

Idle mixture screw should be 1.5 to 2 turns out from bottom.

Three turns out is too much - idle jet is too _small_ (or the idle circuit passageway is partially blocked).

Blocked idle circuit is consistent with poor driveability/stuttering/kangarooing.

(Search for 'redline lean best idle weber' on the web or on this forum)

If it smells of fuel when accelerating that's because fuel is escaping unburnt.

Either it's not making it into the pistons, or it's not being ignited and burnt when in the pistons.

(that's assuming it's reaching the carburettor wells from the pump and not leaking at inline filter, carb inlet,

return pipe, swirl pot etc).

Does it smell bad at the exhaust? Or under the bonnet?

If under the bonnet;

• Likely cause: Split accelerator pump diaphragm

.

If at the exhaust:

• the mixture is too rich.

That's either not enough air:-

• The Weber filter should be okay if you can see pinpricks of daylight through it
• otherwise clean it otherwise the mixture will be too rich.
• Air correctors too small (most noticeable gutless at high revs)

Or too much petrol:-

• Dirty or worn needle valve.
• Float level set too high (less than 7mm gap from top cover with gasket).
• Hole in the floats (sinking floats).
• Jets too large (white smoke and sooty black exhaust)

Other possible causes of poor mpg:

• Sticking choke plate - if the brass UFO pulldown unit is bust, but I think they are near indestructible.
• (in winter) Warmed air inlet pipe and flap mecahnism bust.
• Worn ignition components (cables, rotor arm, plugs, coil, Hall sender).
• Bad ignition timing.
• Cracked petrol hoses (invisible beneath cotton overbraid).
• Fuel tank leak.
• Broken exhaust.
• Broken temperature sensor.
• Leaking/missing/unconnected vacuum tubes.

What box on the bulkhead with a vacuum tube ?

Do mean near the fuses ?

Does it have cables going to it as well ?

You're using a Mk3 bottom end.

Have you got electronic ignition management from a Mk3 injection car on a carb engine ?

It would need a vacuum pipe for the manifold pressure sensor to known when to retard ignition.

Here's the link for redline best idle, I think it's the one?

http://www.redlineweber.com/html/Tech/carb..._lean_best_.htm

I'm interested to see how you get on with this because I'm pretty sure I'm getting crap fuel mileage too. I don't have porting done and just have a basic MH bottom end but I do have a GK manifold which I'm about to fit. Your GT bottom end will surely influence things with jetting, wouldn't it?

All the info above from dvderlm could potentally answer our problems.

I've got standard jets in mine for your reference:-

Primary

idle 45

main 100

emulsion f22

air 155

Secondary

idle 70

main 115

emulsion f30

air 185

Interested in how you end up although probably not comparable to my basic engine.

Good luck

thanks for all this guys the idles are 70 and 45.i had a good look round the carb yesterday replacing the paper base gasket and gasket sealed the rubber seat top and bottom but still eats petrol and is shite when cold.

the rubber seat looks slightly perished an when i revved the engine it seamed to kinda lift slightly.i have ordered a new one from ebay so i guess ill have to wait and see if that solves anything.

can you buy any kind or servcing kit?wheres the best place to buy these etc?

Edited 30 April, 200917 yr by herrod

Here's the link for redline best idle, I think it's the one?

Aye! That's the one. There's a troubleshooter too.

I'm interested to see how you get on with this because I'm pretty sure I'm getting crap fuel mileage too. I don't have porting done and just have a basic MH bottom end but I do have a GK manifold which I'm about to fit.

I've just skimmed some of Hillier's "Fundamentals of Motor Vehicle Technology".

Fundamentals - Inlet manifold design chapter

I'll add

• Poor distributing inlet manifold heating

to my previous list of causes of poor fuel economy.

It appears the GK manifold is good not just because the pipes are larger, but because of the heating which keeps the fuel droplets in suspension and the resonant chamber which I think means the hammer effect when one cylinder's inlet valve closes pulses a wave back and pushes mixture into a cylinder with a just opening valve.

The formula for tube resonance is something like:

3rd pulse length in inches = (1117 * cam_duration/2 * .75 ) / rpm

Hillier also points out that distibuting manifolds need SHARP edges at changes of direction so the turbulence eddies keep fuel droplets in suspension! So I wonder what porting and polishing might have done.

Hard to believe it brings consumption down to about 26mpg 10 l/100km. It's surely some fault.

But herrod's car is better once warm. Is the inlet manifold getting sufficient heat to prevent condensation?

Otherwise I assume there's only underbonnet warmth for the Weber air filter.

An air leak at mounting gasket would also explain why the idle mixture screw has to be so far out.

All that extra unwanted air coming in.

And a smell of petrol.

And if the carb lifts backwards at angle the fuel level will be too high for the holes in the jets

like when driving up hill.

I've bought service kits from fastroadcars. Quick and good.

bo selecta.ill get one ordered how do i find out if its a dmtr or dtml?

DMTLs tend to have a larger/more rounded choke flap. (post a pic and I'll tell you what you've got) They both use the same service kit. If you do have a DMTL you might find it has different venturis to the DMTR that's fitted to the polo. If the venturis are bigger, you tend to need bigger main jets for the same size engine. (multiply venturi size by 5 gives a rough figure. Example, mk2 golf 1.6 DMTL has these jets

Idle 55

Main 120

Air 155

Emulsion F25

Idle 60

Main 125

Air 155

Emulsion F30

That's with 24 and 25mm venturis. The polo weber has 22mm and 22mm venturis. Check behind accelerator linkage on the side of the carb for two numbers stamped there - these are the venturi sizes. With a slight tweak I ran a 1.6 weber on my 1.3 for a good while, fuel economy was excellent too, but performance was flat on the 2nd stage as it was allowing too much air in.

I now have a polo weber on with this setup:

Idle 45

Main 105

Air 165

Emulsion F30

Idle 70

Main 120

Air 165

Emulsion F22

Sounds a bit backwards but I was finding the second stage very flat with the F30 in there. Every engine is different though so it depends on your mods. My engine is a HH with a metal headgasket, GK inlet and ignition, G40 exhaust manifold. Last time I had it RR'd it was putting out 76bhp. (with standard polo jettings listed above by MacColl)

Exhaust manifold heating - the hedgehog preheater thing only operates when the engine's cold. Once the coolant in the manifold has warmed up a temperature switch near the water pipes goes open circuit and knocks out a relay, shutting it off. All post '83 1.3s have water heated & electrically preheated manifolds. I had to convert mine, was a bit of a mission as the head as two holes in it on the inlet side for exhaust gases to come out of! After about two years I finally wired up the hedgehog a few months ago. Does make a difference on cold mornings. :)

theres an oval kinda stamp with 22/22 on the side near throttle linkage

heres a pic of the top

what is this outlet for on the right hand side of the carb?what should it go to

That looks like a DMTR, and the numbers you found are the ones I meant, so it's the right carb. :) Just looking at the plumbing of the fuel lines it looks like you haven't got a swirl pot?

When I used to have one, i put it on the bulkhead, slightly above the level of the carb (to the right of the carb in the pic below)

The brass pipe on the carb I've blocked off on mine as it's not needed, but you can't leave it open like that. Where's the one from the inlet manfiold going? (green pipe)

no i haven't got a swirl pot.ill take a pic of the fuel lines when i get home from work.probly easier than trying to explaine

Because the carb you've got only has an inlet pipe for fuel, you need a swirl pot to send excess fuel back to the tank. At the moment the only thing stopping excess fuel getting into the carb is the needle valve which doesn't sound like it's doing a very good job! :)

Another great thread for info,

Firstly thanks dvderlm for that Hillier stuff which is well interesting. I've got so much literature on carbs now that I'll need to sit down and read between my Uni work.

I have the return on mine so no swirl pot needed.

Gaz does the brass pipe on the right hand side not have to go to the vac on the dizzy? That's what mine does.

The front brass pipe is blocked off on mine which I believe is important.

I've also potentially discovered where I'm loosing coolant (an on going problem involving 3 headgasket changes), was speaking to the engineer who skimmed my head. He reckoned the actual inlet manifold is corroded which is allowing coolant into the chamber therefore into the head. So fitting the GK is hopefully fingers crossed going to solve things.

Finally I'm seeing both of your cars with a K+N bolt on filter. I had one fitted but it was letting dirt into the carb(had to clean jets to often). Is a cleaning kit going to revive it? you know,the kit with the filter cleaner and filter oil.

Once again,

Good luck herrod

I'm actually thinking of going back to a dustbin lid setup on mine because the k&n needs cleaning all the time. As long as you remove the restrictor trumpet from the end they can flow plenty of air. You can replace the trupet with a bit of 70mm hose and direct it to the front of the grille too if the mood takes you.

I think one of those holes is fed by vacuum above the throttle plates and the other is fed by vaccum below the throttle plates. It can make a difference to ignition timing which one you use for the distributor. I think the distributor should be fed from one above the throttle plates but I'm not absolutely certain. I'll have a look at my setup at the weekend. I think I have the front one going to the dizzy (higher up implies it's above the throttle plates although I've never investigated properly) and the side one blocked off.

I remember reading about where to put the vacuum feed for the dizzy in another thread. I've managed to dig it out:

http://www.clubpolo.co.uk/forum/index.php?...t=0&start=0

i cant seem to get my standard air box to fit.the rubber base came today so ill be putting that on on monday.

Yes my standard box didn't fit either. One of the three bolts is out by about 10mm and they are a bit short, so I just unscrewed them and put a bit of thread lock to allow them to sit higher and I made a little plate to catch that third bolt onto the original pierburg plate. I'll eventually be cutting and welding it to make it less of a bodge. If you need pics I can probably get something by tomorrow eve.

that would be great maccoll,I've already butchered one airbox by cutting the plastic when i did eventually get it to sit on the carb it was rubbing on the bulkhead

Here's two shots (in the dark, amazed by how well the flash worked) basically the second shows you how two of the lower bolts line up fine but the top one is out. The little plate is just thin steel that catches the original pierburg plate. My car is a 89 mk2 MH 1272cc, I don't know if maybe you have a different type of filter housing maybe it was on a smaller or earlier type of head? There have been a few different types of these housings.

Hope this helps?