id imagine once the air leaks are cured and youve set it up properly that the original jets will be fine

youve been trying to rejet it to get around other problems imo

Thanks for the advice, I'll look into that. As long as the current set up isn't completely stupid I can do that when I get time.

I tried adjusting the idle today, I had to take the airfilter off to get at the screws, so I blocked off the air temperature pipe. I got it to 800rpm idle hot, choke in and 1,500rpm with choke and the mixture screw was turned in as much as I could get it without reducing RPM (now when I wind it out all the way the engine stalls btw). I put the air filter back on and it's idling at about 500rpm without choke and right on the brink of stalling (but doesn't)... guessing that's the resistance from the filter so I'll need to increase it. Not tried it cold yet got to do that tomorrow morning.

I did try blowing through the pipe into the vacuum advance on the distributor, someone mentioned that it might be causing a vacuum leak, and there is no resistance at all to me blowing through it apart from the width of the pipe. Should I be able to do that?

you can reach both ajustment screws with the aircleaner on...as you say it will alter once its taken off

its a bit tricky but you can just about feel for the idle screw by hand....

Yeah, I'll have another crack at it tomorrow.

I did try blowing through the pipe into the vacuum advance on the distributor, someone mentioned that it might be causing a vacuum leak, and there is no resistance at all to me blowing through it apart from the width of the pipe. Should I be able to do that?

That might imply the diaphragm in the distributor vacuum advance unit is split.

Normally you test this pipe (and the unit) by sucking on it and see if it sticks to your tongue.

I'd try sucking on some clean new pipe myself...

I I'd try sucking on some clean new pipe myself...

quote of the week

Vacuum advance has definitely gone, I tried fitting a new one today but I couldn't get at the bottom screw. Looks like I need to take the distributor off. For now I've just plugged the pipe with a large bit of blu tack and duct tape.

At the moment it runs pretty good hot, doesn't drink fuel either. It has problems starting from cold though, it takes several tries. It will fire up for about a second then drop off. To keep it going I have to rev it right up to about 3k for a few seconds and it misfires for a bit then its ok.

Starting it this morning was a job in itself (it's been very cold), with the choke out it started up but the revs slowly dropped off until the only way I could get it to run was to keep my foot on the accelerator with the choke fully in until it warmed up, so it took me 15-20 minutes to get going after i messed around for a bit. Vacuum pipes have no leaks, replaced most of the ignition system now (sparks, leads, cap, rotor, coil). I'm looking out for a DMTR carb instead because this is just getting ridiculous.

have you messed with the fast idle and idle screws at all?

set up the mixture?

(bad weather, holidays, stuff...)

I tried setting the carburettor up again yesterday. I waited for a good 30 minutes to get it warm. Got the idle speed, mixture and fast idle set up properly so it was 1,500rpm fast idle, 800rpm normal with the mixture screw in just before the point where it starts to reduce engine speed.

I took it out for a drive and it seemed OK for about 10 minutes driving, then whenever I let it idle it would drop to about 400rpm and sit there chugging away. Few minutes later it just kept stalling and wouldn't restart unless I had the throttle open. I opened up the mixture screw a bit and that seemed to help for about 5 minutes before it started doing it again. Screwed it out further, fine for a few, then starts slowing up and dies.

The vacuum advance is still disconnected, but the pipe is blocked off and the air temp pipe is fine too. It has the hot air feed connected to the airbox. It seems alright idling until I actually drive it, then it starts to have problems.

hmm doesnt sound good

cant help but think it wouldnt drive well at all with no vac advance

sounds like the 400 rpm is choking from being rich maybes...I'm losing track now , but did you put the orig jets and stuff back in?

No, it's running richer than normal jets (primary is richer I think), idle should be the same as stock.

EDIT:

Main: 115/120

Air Corrector: 155/185

Emulsion Tube: F22/F30

Idle: 45/70

I think that's normally 100/120 or something like that.

Edited 16 January, 201016 yr by anessen

i personaly wouldnt have changed the jetting at all ...in my opinon it should be close enough to run okay

i feel you was mislead people saying re jet it , theres either a fault in the carb , fitted badly or set up badly (plus the advance needs fixing) i cant really offer up much more ...think its time to let someone have a look , either someone off here or a decent garage that knows webers

good luck

Edited 17 January, 201016 yr by steveo3002

I agree, think you need to team up with someone and eliminate what could be a number of issues. Put it this way my car was a non runner when I got it but started up 1st time on old fuel but wouldn't idle with the Pierburg. So the next time it was started with the weber DMTR with standard jets and it ran effortlessly with a bit of choke and then a few minutes later without. Admittedly it runs a bit rich but thats going to take some subtle adjustments on a rolling road.

I appreciate it's hard to get help, I only know one friend who knows about cars but he didn't have the knowledge on the carb that I had. He could however eliminate other potential issues. Try and get someone from here maybe local to you involved or a helpful oldskool garage.

Good luck

(bad weather, holidays, stuff...)

snip. It seems alright idling until I actually drive it, then it starts to have problems.

It's always diffficult to diagnose at a distance. I'd be happy to have a look.

You anywhere near next weekend's rolling road event at Aldon automotive?

There should be a high density of Polo enthusiasts and I even think Aldon are Weber dealers.

Anyway :

At warmed up idle the only things involved inside the carb are the idle jet, the well, the float, the throttle flap and the mixture screw.

Since it idles fine before it's driven a 45 idle is okay. You could make sure with a CO2 exhaust probe or a Gunson Colortune. And we have to assume these things are all setup close enough to good settings for a static system to keep working.

What changes when you drive it?

There might be some crud in the well being sucked onto the bottom of the idle jet.

But it's new carb with a new filter, new pipes(?) and a swirl pot so I'll discount that.

Before blowing the idle circuit with compressed air I'd use the RAC patrolman trick to suck through any such crud.

Or maybe the throttle plate is sticking open or closed yet the 34DMTL choke lever has a cam which opens the throttle butterfly slightly when choke is first applied and you've set idle speed right with hot engine - so unless that cam is damaged,.. Shine a torch down past choke flap to see the throttle buterfly flap move smoothly. But it's new carb so I'll discount that too.

And setting off would be very bucking bronco like.

Disconnected advance. The extra retard of the spark timing is not happening other than by sprung weights or a Hall sender and simpe TCI-H lookup table but it'll still run perhaps not as efficiently and back at idle who cares.

So it's a different dynamc problem at idle.

Under load more fuel is sucked by the pump. More than when revving the engine by hand in neutral.

And to me the symptoms sound like rust/sludge in a fuel line (feed or return).

The well becomes slowly exhausted after driving a bit because insufficient pressure is psuhing fueil in past the opening inlet valve as the float falls leaning the mixture so the revs drop and eventually you stall. Often you can wait a while and the sludge will fall back down the fuel pipe under gravity. Car restarts on the accelerator pump jet shot. There's then sufficient flow at idle to refill the well and let you drive for 10 minutes or more at moderate speeds.

Other symptom of sludge is bubbles in the fuel filter or fuel lines.

There are some black deposits on the outside of some of the jets and some white stuff on the outside of the primary main jet.

When I'm driving it seems to have a decent amount of power but the jets are set up to run richer than what should be necessary. I have the idle set higher (about 1,000 RPM) and it doesn't dip down to the point it stalls when its hot, but when it goes to idle it does dip below that for a couple of seconds then comes back.

Smaller primary does make it run too lean, I can feel it surging on the accelerator pump and then dropping back slightly.

It does look like theres some crap in the carb now, whats the best way to get that out without taking the carb apart?

Carb cleaning without dismantling.

If car will idle, first use the RAC patrolman trick.

Remove the air cleaner.

Lightly put your hand over the chokes and rev the engine using the throttle quadrant.

There's hardly any air so just petrol washes through the jets taking small crud with it.

It might make large crud stick in a jet.

It is the suction of 50 vacuum cleaners so your hand will be hard to remove

even after the engine has been stopped. Red circles indicate good compression.

Now remove and dismantle each jet. They should pull apart by hand.

Small pliers sometimes needed, gently - brass is soft.

I do primary first: idle then main on primary side then replace main then idle.

Idle jet is most likely to be blocked as smallest. Idle is two part: jet and holder.

Main is three part, jet - emulsion - air corrector.

Hold them up to the sky to look through them.

If you just ran the engine and the jets are dry then either your needle valve is stuck closed:

perhaps your floats are resting on a sidewall or a fuel filter or inlet line is clogged.

Sometimes you have to bend apart tube lugs for a tight fit on reassembly.

Always put main back first - getting an idle jet out of the main hole

is hard. I suggest a sharp pointed jeweller's screwdriver into soft brass or

superglue or turning the car upside down will all do the trick.

After replacing primary jets - so no chance of mixing them up - clean secondary idle then main and replace,

Once again always replace secondary main before secondary idle.

Cleaning a jet usually just requires blowing through. Your mouth is fine but

a compressed air keyboard duster plus short length of windscreen washer tube

works well. You really can see the aerosol atomization of the fuel

by the emulsion tube. Make sure no naked flames nearby!

Stubborn cases need soaking in carb cleaner - which appears to be

xylene based. I guess nail polish remover, dry cleaning fluid, meths, or even petrol would be okay.

Finally clean the idle circuit. This does need compressed air and a tube.

Carefully screw in the mixture screw counting the 1/2 turns.

Note the start position of the screwdriver and final position.

(I use a screwdriver with a bit of tape to make it visible).

Unscrew the mixture screw. Pull it out (there's a rubber grommet).

Put tube into the mixture screw hole. Blow compressed air through.

It should bubble in the well. Refit idle screw all the way in gently,

ensure screwdriver at same position then rewind out to original counted 1/2 turns,

Make sure screwdriver reaches same position. This saves having to reset mixture if it

was previously correct (if it wasn't right, google for redline's lean best idle method

or use a Gunson Colortune to set the idle mixture).

You can't clean the pump jet with this method, but you can suck the well clean of petrol using a hand

pump and a thin tube down a main jet hole. With luck this will pick up anything that came

in through the needle valve.

Nice one, thanks. I'll have a go this weekend. The car does idle fine so hopefully this works.

I took the air filter cover off while the car was running to have a look and I could hear popping/spitting noises coming from the carb. Another symptom of crap in the fuel?