1.8l carb issues: oil in the airbox, sticky throttle

Just got back from Wörthersee, so now I can have a look at the problems that developed while I was out there! I get the occasional nasty smell and puff of white smoke through the bonnet vents while driving - especially when the engine's thoroughly warmed up when I corner enthusiastically. Had a quick look and there's a small drip of oil from the back-left corner of the joint in the airbox (the one you split to get the air filter out). When this drips it lands square on the exhaust manifold, hence the smell and smoke…

I've cleaned it all out with a bit of rag but it just recurs. The air filter isn't saturated with oil, but it's present all along the lower edge of the rubber seal. I assume it's coming from the crankcase breather, but why so much? Don't think it's overfilled, the level's in the centre of the dipstick…

The engine's been running a bit fast (combination of a sticky throttle cable with a poorly-adjusted idle - doesn't seem to respond to the idle screw on the carb, but maybe I've been tweaking it wrong?) and it's had a fairly long motorway run back from Europe at 3000-4000rpm, but it happens in town driving too so seems to be here to stay.

Any ideas? Not hugely keen on getting used to smoke from the engine bay, as you can imagine! Stone

Mini update to this, as I was digging about trying to work out what model of carb is fitted. Here are a couple of pics of my carb (nb: it's an auto so may differ from manual ones..?): I'm pretty confident it's a Weber 32/34 DMTL but looking at internet pics it seems the throttle linkage is different. I'm missing the return spring from the bracket on the right-hand side, but there's no place to hook it up on the linkage I have, and the spring's mounted directly on the throttle cable instead. Maybe swapping this over would help with my non-returning throttle issues…?

See these examples:
Stone

yah is a weber, lack of spring may just be an auto thing but not 100%.

anyway yes you will see some oil in the airbox this is normal, if the breather mesh (if fitted) is blocked it can make  the block breathe a bit heavier but the trouble is if it has a mesh these are next to impossible to clean as they are multi layered mesh stacked together. some have had success chopping out for proper cleaning, or getting other random mesh and welding back in.

if its leaking out the airbox tho it could be its loose or seal is missing

And your choke cable seems to be not fitted correctly as it's bending when the choke if off and I don't think it's set up right as the gap between screw/bolt and the metal bracket which moves when you pull the choke out to increase the idle looks to big, how does the car start/idle when cold?

It won't start at all without any choke (just revs and instantly dies), normally needs 1/2 to 3/4 choke for 2-4 minutes but then the choke can all be closed at once and it runs fine. It also won't start sometimes if the choke's 100% out, it struggles and coughs (eventually stalling) until the choke's pushed in a little.

It also needs to run in P or N for 10-20 seconds when first started, putting it into a driving gear stalls it - again it runs fine after it's slightly warm.

Would it be worth pulling a bit more of the choke inner cable through then, so it's tighter? Wondering if it was left that way to account for the non-returning throttle arm. Operating the throttle lever progressively, the choke butterfly opens at the end of its travel so that seems to be working as expected.

The airbox was all replaced by CQ recently as the previous one's front rubber mount was snapped off.

Is there supposed to be a seal between front and halves of the airbox? I only have the rubber lip around the air filter sandwiched into that gap at the moment. I guess if there's an air leak it has to be upstream of the carb to cause increased idle speed, so the seal between carb and airbox is propbably ok. The top bolt holding airbox to carb is definitely wrong, it's just a regular hex bolt and (bent) washer when it looks like it's supposed to have a top-hat washer - might see if I can get something machined up, but I don't know if that would improve the del. Might stop it vibrating loose, mind…

Stone

theres no seperate seal between the 2 halves of the airbox, thats done by the air filter there is one between the airbox and carb though, probably 037129625A as I assume its EW/EX engine right?

the EW/EX airbox it would be clipped on originally but since you have a weber you loose the clip and instead it is bolted down, the proper hardware is like an odd T shape nut that threads down onto a stud on the bracket. its shaped this way to slip nice down the hole in the airbox and tighten fully to the bracket, if you dont have this then a self-lockign nut should help or find a sleeve that drops down the stud so a nut and washer can tighten proper

Yep, it's an EX. Is the seal the same for both Weber and Pierberg? Might be worth changing just for added confidence.

I don't have the correct fixing hardware up top, just a bolt and washer - if it's vibrating loose it might explain why it gets a faster and faster idle over time - thought it could have been a heat issue…

I have two single piece clips on the top of the airbox and one jointed one either side, is that the right number? Maybe they're not holding the halves tight enough as the oil drip is from the bottom.

Stone

yeah the bottom seal is the same, if its there you wont need to worry. as you say any air leak upstream of the carb wont affect the running just means a bit of unfiltered air can get in. but with all the oil and rubbish that comes in from the breather a little more dirt cant really hurt

a self locking nut should stop it working loose, but the worst thing that can happen with a loose airbox other than rubbish getting in the carb is the warm air feed will loose vacuum and eventually you might get a bit of carb icing, it wouldnt affect the idle really

the clips all sound right, probably just too much oil to seal against affectively. you could get yourself a catch tank to stop the oil, I rigged up a milkshake bottle temp just to see if crank case gasses were affecting anything. once it was clear it made no difference i put it back.  as i say maybe the mesh in the rocker cover if there is blocked causing excessive breathing?

It was icing up a little recently (same symptoms as when the foil pipe tore open a couple of years ago - replaced it with a silicone one) so maybe the seal's not 100%. Looking closely there's a tiny hole in the right place in the throttle arm for a return spring so I might add one of the Weber ones as well - can't hurt. The pedal cable runs to the gearbox and then a second cable from the gearbox drives the carb on autos, so it's got a bit further to go…

Adjusted the choke cable a little - runs a little better now but the outer cable's not clamped very well, feels like the thread on the clamp may have stripped. Hoping a new spring, seal and air filter might calm it down a bit, if not I may just have to live with it

Stone

Had a thought: am I supposed to have one of these on the dipstick tube? If so I may have been overfilling the engine!

Pictures of my carb, it's slight different from your's as it's off my Mk1 Scirocco, manual and it's at Webber DMTR.
Set up of choke cable and the adjustment of the screw (circled in red) which when you pull the choke cable out increases the idle speed by opening the throttle, there is a light gap so the screw is not touching the throttle adjustment when the choke is off but it's not easy to see in the photo.


Set up of spring, it was orginally attached in the little hole but after a couple of years it started to make the hole bigger and I thought it might wear it's way through the metal to moved it to the bolt which holds the accelerator cable but just keep an eye on yours.


As for the dipstick tube have you got a picture of what type of dipstick you have, a picture of it in the engine and out of the engine would be good?
I've one of those tubes on my Golf but not one on my Scirocco so you may not need it

yeah you deffo should have one on your cabrio, thats probably why it keeps spitting out so much oil

edit: they came in 31/7/1983 onwards

False alarm, sorry. Didn't know they came in colours other than orange!

yeah that one is fine

It's really getting sad now The surging / intermittent loss of power is now happening from cold at anything above around 3000rpm, which restricts me to about 50mph. Any more throttle and it really struggles and I have to back off to under 2000rpm to recover it. Feels the same as when my warm air duct hose tore way back when (ie carb icing) but the hose is now a silicon one and secure to both the deflector and airbox.

The warm air flap vacuum feed seems ok - putting a finger over the end when it's hot it alternates between very slight vacuum and a bit stronger, so I guess that's probably ok? Haven't checked the actual flap yet, maybe it's gunged up and stuck closed?

The airbox is still secure to the top of the carb so I don't think it's vibrating loose. Will be taking it all apart for a clean and a new air filter later but I'm not wildly hopeful…

I've also gained an intermittent rattle / knock underneath somewhere, had trouble with the middle exhaust mount before so hopefully it's just loose? Doubt the engine mounts are very happy either, the dieselling when I turn it off and the surging can't be doing them any good!

Stone

Just a thought but I did read somewhere about restricting the fuel return to fuel tank?
I'll try and find it….

Found it, does this sound likr your problem?
http://sciroccoregister.co.uk/carforum/viewtopic.php?f=12&t=15397&p=108435&hilit=Restricting#p108435
 

Stone said

Doubt the engine mounts are very happy either, the dieselling when I turn it off and the surging can't be doing them any good!

Stone

What do you mean by "dieselling when I turn it off"?

mark1gls said

Just a thought but I did read somewhere about restricting the fuel return to fuel tank?
I'll try and find it….




Found it, does this sound likr your problem?
http://sciroccoregister.co.uk/carforum/viewtopic.php?f=12&t=15397&p=108435&hilit=Restricting#p108435

That does sound exactly like it, actually. Not sure why restricting it would help though - and why are people removing the vapour separator also? Wouldn't VW have left it off if it was unnecessary? 

mark1gls said

What do you mean by "dieselling when I turn it off"?

When I turn the ignition off, the engine stops, then coughs a couple of times and either stops completely or comes back to life, runs really rough for another second or two and then stops. Since the coil's disconnected with the ignition off, the spark plugs shouldn't be firing and it's most likely that residual heat in the cylinder walls is providing enough heat to ignite the fuel that's admitted by the carb. - that's why it stops after a second or so as the cylinder walls cool and the fuel stops igniting. It's called dieselling because the engine's running by compression ignition, like a diesel engine…

Edit: just popped over to our machine shop and been gifted a 0.8mm MIG welder tip. Is trying it out as obvious as removing the vapour separator, tapping the return feed to M8 and inserting the tip? (after a good clean, naturally!) Would ideally like to get it sorted before I try to drive home as doing such low speeds on the motorway is quite unsafe…!

Stone

Just taken the inlet off for the umpteenth time. Looks like someone's trodden on this airbox so that might explain why it doesn't seal properly and drips oil on that side…

Taking the return pipe off the separator, there is a restriction already in the pipe - but the hole in it is huge. Going to try removing it and fitting the MIG tip instead for the drive home…



Stone

Just got home and it was fine all the way

I realised the MIG tip was too big to tap into the separator (unless I snapped off the outlet and tapped into the hole, but I couldn't see how to take it apart so didn't want to get bits of swarf stuck on the inside…); the old restrictor was just stuck into the pipe so I gave the new one some WD40 and forced it in, then put the pipe back. Changed the air filter while I was there just in case, old one looked alright but the new one has a thicker foam-type seal so might stop the oil a bit better!

Comparison of old with new:


The old one was almost equal in size to the bore of the fuel hose, and it looks like it's stretched slightly over the years so fuel could get all around it as well as through the big hole in the middle. The new one is quite substantial and thoroughly blocking the pipe off so none can get round the edges…and it suddenly feels a lot sportier! Revs much more easily and needed choke for far less time to get it going well. Fingers crossed but it may be sorted, I'll give it a week or so to recur just in case

Thanks for the help!

Stone