Mk 1 Cabriolet Pierburg to Weber Conversion

I moved to Cyprus 20 years ago and brought my 1990 Mk 1 Clipper automatic with me - only 57,000 miles since new showing on the odo.

The expansion element (waxstat) was changed by VW 25 years ago but I believe that it is playing up again - fast idle at 1800 rpm and overrun when I switch the engine off.

The Pierburg had new gaskets fitted by the local garage in my village to stop a fuel leak and the old man seemed to know what he was doing despite the language barrier.

I do not have a garage so I cannot play with the element.  I am going to ask him to remove the element, give it to me to plunge in boiling water, then refit it.  If this does not work then a Weber conversion seems to be the way forward.

I note the Weber has a manual choke.  Is there any drilling involved or does it slide through somewhere?  Where is the best place on the dasboard for it?  I am a little hesitant to let Costas just "drill, baby drill".

Any advice greatly appreciated.

I can't help with Weber conversion, but have some experience on the Pierburg 2E2. Is the idle speed excessive in all conditions or just during warm-up? Do the coolant hoses feeding the wax stat and choke get hot as the engine warms up? A blockage in that coolant path would interfere with both wax stat and choke operation  Corrosion byproducts in the coolant channel of the choke housing caused mine to idle excessively high through and after warm up.

Overrun after switch-off doesn't sound like a wax stat issue

typ_53b said

I can't help with Weber conversion, but have some experience on the Pierburg 2E2. Is the idle speed excessive in all conditions or just during warm-up?

All conditions

 Do the coolant hoses feeding the wax stat and choke get hot as the engine warms up?

Yes!

A blockage in that coolant path would interfere with both wax stat and choke operation  Corrosion byproducts in the coolant channel of the choke housing caused mine to idle excessively high through and after warm up.

Overrun after switch-off doesn't sound like a wax stat issue

Thanks for posting.

Yeah, a faulty wax stat may well cause the fast idle issue. I'm a bit dubious about the benefit of immersing it in hot water - the coolant flow should approach 90 degrees or so when the engine is run to full temperature.

However, as you also have a problem over-running , I am wondering if both issues could be caused by a fault related to the 4-point unit (throttle plate actuator), which would likely be vacuum related.

This relatively recent video gives an overview of idle speed control components on the 2E2 carburettor and highlights a few easy observations you can make to check they are working properly - probably the most informative and accurate explanatory video I have seen on this topic:

Pierburg 2e2 carb, function and problem solving - YouTube

typ_53b said

Yeah, a faulty wax stat may well cause the fast idle issue. I'm a bit dubious about the benefit of immersing it in hot water - the coolant flow should approach 90 degrees or so when the engine is run to full temperature.

However, as you also have a problem over-running , I am wondering if both issues could be caused by a fault related to the 4-point unit (throttle plate actuator), which would likely be vacuum related.

This relatively recent video gives an overview of idle speed control components on the 2E2 carburettor and highlights a few easy observations you can make to check they are working properly - probably the most informative and accurate explanatory video I have seen on this topic:

Pierburg 2e2 carb, function and problem solving - YouTube

Thank you again for posting.

I was wrong in my previous repy - the choke gets warm but not hot.  I am off on holiday tomorrow so research will have to wait until I get back in 6 weeks.

Thank you for the link!

Marc C said

typ_53b said

Yeah, a faulty wax stat may well cause the fast idle issue. I'm a bit dubious about the benefit of immersing it in hot water - the coolant flow should approach 90 degrees or so when the engine is run to full temperature.

However, as you also have a problem over-running , I am wondering if both issues could be caused by a fault related to the 4-point unit (throttle plate actuator), which would likely be vacuum related.

This relatively recent video gives an overview of idle speed control components on the 2E2 carburettor and highlights a few easy observations you can make to check they are working properly - probably the most informative and accurate explanatory video I have seen on this topic:

Pierburg 2e2 carb, function and problem solving - YouTube

Thank you again for posting.

I was wrong in my previous repy - the choke gets warm but not hot.  I am off on holiday tomorrow so research will have to wait until I get back in 6 weeks.

Thank you for the link!

Back home in Cyprus now.  At normal running temperatures, the hose from the inlet manifold to the autochoke is haerdly warm at all.  I assume the hose to the waxstat comess from the autochoke.

I agree, there must be a blockage somewhere and I am beginning to think the grommet in the inlet manifold must be blocked.  Could the blockage be somewhere else?

I toyed with the idea of removing the waxstat to test it but it looks as if I have to remove the carb first which is way beyond me.

Can the waxstat be removed without disturbing the carb?  If so, what needs to be removed?

I will be working outside - how I am missing by UK garage, sigh…

I renewed my wax stat with the carb in situ, and can't remember any particular access issues. I had previously had very poor coolant frow through the wax stat and choke, which made me fear the inlet manifold grommet, but it turned out to be oxidation of the aluminium surface within the coolant nozzle of the choke cover - I imagine where an air lock had formed while the car was in storage for 9 years. I took my choke cover apart to clean it out and fitted a new o-ring seal, but it could probably have been cleared through the nozzles. That was 8 years ago and it has been fine since

Thank you very much for the additional information.  I will go and have a closer look to see what options I have.

If not, perhaps I should take the car to Costas to sort it out.  When I asked him to fix a coolant leak I said that I was concerned that it might be the inlet gasket which I showed him.  He asked me if I had the grommet as well (which I did).  This suggested to me that he knew all about the issues with the 2E2 carb installation so I will at least have confidence in his work.

He sorted out the coolant leak  - replacing a fitting near the front of the engine.  

I might be partly responsible….  I had always thought that the antifreeze in the radiator was to prevent the water from freezing and, since I was now in Cyprus near the coast where it doesn't get down to 0C, it was alright to top up the coolant with distilled water.  

It was only when my neighbour noticed what I was doing that I found out about the anti corrosion properties of antifreeze!

Marc C said

…If not, perhaps I should take the car to Costas to sort it out.  ..

Booked in for next Tuesday.  He agreed that the hose from the inlet manifold to the autochoke was cold and that it should be hot - but he is sure that the grommet in the inlet hose is not the problem.

I shall report back.

A little disappointing…….

Costas said that he had cleaned the carburettor and made adjustments.  Car now idling at 1,200 rpm but the hose to the autochoke is still cool.

I will take it out on a run tomorrow and if the hose is still cool I will go back to him.  Cyprus shuts down for Easter so It may have to wait until next week.

Would anyone care to estimate how many man hours it would take to change the inlet manifold gasket and grommet?

Not an easy job, certainly - access with engine in situ  looks challenging. Could the coolant flow through the inlet manifold be tested before dismantling?

Has Costas checked for free flow through the wax stat and the choke cover?

typ_53b said

…Has Costas checked for free flow through the wax stat and the choke cover?

Thank you for the suggestion.  I will suggest same next week (without hurting his feelings!).

Marc C said

…I will take it out on a run tomorrow and if the hose is still cool I will go back to him….

45 Minutes on the motorway followed by 15 mins slow traffic - the fan was running when I shut the engine off.

The hose to the autochoke was hotter than it has been but not as hot as the upper radiator hose when I almost burnt myself.

Does this suggest that there is some flow through the autochoke I wonder?

The engine idles at 1,200 rpm and will "run on" with a few knocks before shutting down.  If I leave it in drive but with my foot on the footbrake and turn off the ignition it shuts down instantly.

Yes, it sounds like a very small flow of coolant is seeping through, but not enough to operate the warm-up system correctly.

1200 rpm is a pretty fast idle, from memory it should be between 900 and 1,000 rpm on auto gearbox versions (700-800 rpm on a manual). The idle settings will of course have to be reset, once the  warm-up system is functioning as it should

typ_53b said

..1200 rpm is a pretty fast idle, from memory it should be between 900 and 1,000 rpm on auto gearbox versions ''

Mine is an automatic so I know what the target should be.

If Costas is unable to find anything, would I be wasting my time flushing the coolant system with something like Wynns radiator flush?

I don't know anything about coolant system cleaners, but I guess it would depend on the type of blockage and would obviously only work if a significant amount of coolant is getting through

typ_53b said

…. and would obviously only work if a significant amount of coolant is getting through

Yes, that makes sense.  Let's hope Costas can sort it out.

Marc C said

… would I be wasting my time flushing the coolant system with something like Wynns radiator flush?

It would appear so:  Jetta Troubles

Marc C said

… Let's hope Costas can sort it out..

Went back to Costas.  He assures me that he cleaned out the autochoke and the carb and that the temperature of the coolant hose and autochoke is hot (I think they are warm).   He explained that the bore of the hose from the manifold to the autochoke is small - he estimates about 2 mm - so that coolant hose will not be as hot as the upper radiator hose.

Sounds genuine?

A few days later the hot idling speed dropped to 200 rpm!  I went straight to Costas.  He stopped what he was doing, removed the air box, and fiddled with a screw at the bottom of a 2 inch tube pointing up.  As he adjusted the screw left and right the idling speed varied but eventually settled at 1,000 rpm so I left a little happier.  It seemed to me that he was adjusting the mixture screw but it all works now.

Was he adjusting the mixture screw or was it really the idling screw?

I recently adjusted my 2E2 carb settings after adjusting the ignition timing to suit super unleaded (98 RON) petrol. Due this petrol being unavailable in the UK at the time of manufacture (1992), legislation had been introduced that required the timing to be retarded to allow use of 95 RON unleaded, slightly reducing performance and efficiency. However, now that super unleaded is widely available, it made sense to restore the engine's design parameters.

Idle speed is controlled via a 13mm hexagon headed screw on the back of the 3-point unit (4-point for automatic engines). This is on the rear left of the carb when viewed from the front of the car. This is very awkward to access, which probably explains why it is often overlooked. Idle mixture is controlled via the vertical screw in the tube at the top of the carb - the one you mention. This operates in the opposite direction to most mixture screws - clockwise to enrich, anti-clockwise to weaken.

I can confirm that the choke housing should get burning hot to touch once the engine has fully warmed up. The coolant channels through the wax stat and choke housing are probably around 8 mm inside diameter. As I mentioned before, the coolant channel through the choke housing had virtually blocked with aluminium corrosion sludge when I first bought the car, but having cleared this out 8 years ago, fitted a new wax stat, and readjusted the warm up cam (which had previously been incorrectly adjusted to compensate for the faulty wax stat), the carb still works perfectly