Club 80-90 Forums

Thanks for replies.
I am sticking with the Weber until I change everything back to Digifant.
I sourced a rebuild kit from Eurocarbs, and I have an ultrasonic bath at my disposal so should make a difference

P.S. I have long since removed that fuel filter it was the first thing I did

kevtherev wrote:

ajsimmo wrote:Yuk! I would just bin it. Pierburg 2e3 is still available new from VWClassic for £400 odd. Would run beautifully (if all else is in good nick).

X2

Does anyone have any real world experience with these Weber 34 DAT carburettors?

I'm just curious as I am currently rebuilding mine and have taken note of all the jet sizes so if there's a better combination I'd like to know?

Also why is this carb "not suited for a wbx engine" I have come across this comment a lot on various forums but no information to back it up.
Obviously my running issues aside until I confirm it is in a serviceable condition.

Many thanks.

I have no idea about recommended jet sizes, there appears to be some carb snobbery around this Weber conversion, I have had one of these fitted to a 1.9DG now 2.1 MV with no issues whatsoever for the past 5 years( the previous Pierburg had second stage vacuum pull down issues and obsolete parts)
you should have no problems if it is set up correctly

P.S sourced from Southern Carburettors and supposedly jetted for the 1.9 as a replacement kit.

weimarbus wrote:P.S sourced from Southern Carburettors and supposedly jetted for the 1.9 as a replacement kit.

Thanks for reply, I believe the fuel air ratio is the same for 1.9's and 2.1's therefore this conversion kit jetted for a 1.9 should go straight on a 2.1 with no problems as you mention.
Is your power delivery smooth at the bottom end of the rev range? This is where I was having jerky issues and erratic / no idle so if it does not go away I may try changing the primary idle and main jets...

The proof is in the pudding today as I'll be fitting my rebuilt carb, wish me luck!

The air/fuel ratio (afr) changes dependant on fuel not by engine, running on petrol the magic number is 14.7 - 1.
The main issue with the weber carbs is the choke size (the venturi the air passes through), the pierburg uses quite a small choke size for the engine size meaning that the air speed is very high, this means that a small jet is needed due to the vaccum acting on it leading to smaller droplets of fuel which will stay in suspension longer through the very long inlet tract of the boxer engine, the weber carb by comparison has much larger choke sizes meaning the air speed is lower as is the vaccum acting on the jets meaning bigger jets are needed leading to bigger droplets of fuel which fall out of suspension quicker.
The weber carb is a good unit and on most applications where it is used to replace the 2e pierburg it is generally an improvement, however the volumetric efficiency of the boxer engine is quite low so not ideal for getting the bigger chokes working properly at low engine speeds and small throttle openings, obviously the more wear on the engine and the resulting lower compression figures will only make it worse.

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AIR_CHILLED wrote:

kevtherev wrote:

ajsimmo wrote:Yuk! I would just bin it. Pierburg 2e3 is still available new from VWClassic for £400 odd. Would run beautifully (if all else is in good nick).

X2

Also why is this carb "not suited for a wbx engine" I have come across this comment a lot on various forums but no information to back it up.

Many thanks.

No Idea. Million of cars from loads of different manufactures where fitted with Webers including flat four Alfa's.

One of the problems people just fit them and expect them to work without set them up. As they where not an original fitment then they have to be tuned to the engine. Jet sizes and float level determined preferably on a rolling road.
Vac advance signals vary between different types of carburetors so the vac advance can should be matched to the signal. Webbers have a softer vac more like the air cooled engines than the stronger "WBX Pierburg.


I see you have fundamentals of motor vehicle technology written by my old college lecturer Vic Hillier.

MGP wrote:The air/fuel ratio (afr) changes dependant on fuel not by engine, running on petrol the magic number is 14.7 - 1.
The main issue with the weber carbs is the choke size (the venturi the air passes through), the pierburg uses quite a small choke size for the engine size meaning that the air speed is very high, this means that a small jet is needed due to the vaccum acting on it leading to smaller droplets of fuel which will stay in suspension longer through the very long inlet tract of the boxer engine, the weber carb by comparison has much larger choke sizes meaning the air speed is lower as is the vaccum acting on the jets meaning bigger jets are needed leading to bigger droplets of fuel which fall out of suspension quicker.
The weber carb is a good unit and on most applications where it is used to replace the 2e pierburg it is generally an improvement, however the volumetric efficiency of the boxer engine is quite low so not ideal for getting the bigger chokes working properly at low engine speeds and small throttle openings, obviously the more wear on the engine and the resulting lower compression figures will only make it worse.

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Wow thanks MGP that is exactly the sort of answer I was looking for.
This helps explains the precise symptoms I have which is under partial throttle and low engine speeds (under 2000 rpm) it hesitates / kangaroos but is perfectly smooth and powerful further up the rev range.

So as I can't do anything about the size of the venturi on the primary barrel could I fit smaller primary idle and main jets?
And... if I posted up the sizes could you recommend an alternative size to try?

Now as you mention fuel suspension it occurred to me that the manifold to coolant preheater is not connected and blanked off!
Could connecting this create warmer inlet temperatures and help keep more fuel atomised / in suspension?

Thanks.

bigherb wrote:

AIR_CHILLED wrote:

kevtherev wrote:
X2

Also why is this carb "not suited for a wbx engine" I have come across this comment a lot on various forums but no information to back it up.

Many thanks.

No Idea. Million of cars from loads of different manufactures where fitted with Webers including flat four Alfa's.

One of the problems people just fit them and expect them to work without set them up. As they where not an original fitment then they have to be tuned to the engine. Jet sizes and float level determined preferably on a rolling road.
Vac advance signals vary between different types of carburetors so the vac advance can should be matched to the signal. Webbers have a softer vac more like the air cooled engines than the stronger "WBX Pierburg.


I see you have fundamentals of motor vehicle technology written by my old college lecturer Vic Hillier.

A rolling road tune may be the ideal solution but the extra cost is something I'm trying to avoid. This carburettor is a temporary set-up and needs to see me through the winter camping months however in the Lake District last weekend the lack of bottom end power on steep climbs was beyond frustrating!!
Nice spot by the way with the book it's great! My friend who's an automotive engineer lent it to me as I mentioned I wanted to rebuild the carburettor.

I fitted the rebuilt carb today and apart from helping with the erratic idle and stalling the low end power is still hesitant and lacking

Does anyone have a Pierberg lol...

A cold manifold will cause the fuel droplets to stick to the manifold so best to get that sorted to start with.
Next up i would get a dti on the rockers and measure the lift on the cam, whilst there check that the preload on the lifters is bob on, the VE on these engines is poor to start with if the valve train isn't bob on the losses will be high.
Check all the gaskets between heads and manifold, and manifold and carb, also are you still running the insulator between the carb and manifold? Check all vac lines and the diaphragm in the vac advance, once you have eliminated any chance of an air leak and you know that your not loosing any VE then you need to know what is going on with the afr during the transition from the idle jet to the main jet as this sounds like where your problem lies.

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Another thought what distributor are you running?

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MGP wrote:Another thought what distributor are you running?

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I have sourced and fitted a DJ dual vac distributor along with new plugs, leads, ignition amp and coil all from Brickwerks.

Ignition wiring loom from mk2 golf with no idle stabiliser connected.

Vac lines are new and retard connection on vacuum diaphragm is blanked.

Timing is been set at 5 degrees BTDC

Full advanced (dynamic) checked: 35 degrees BTDC at 2000 rpm

This was all done previous to looking at the carburettor because this is where I thought the problem lied. The Previous owner but one had fitted an Aircooled ignition system.

Also cheers for your above post, some more checks to consider.

There is a thick plastic black spacer between adaptor plate and carb so I'm assuming this is the insulator.

All gaskets checked and replaced or remade.

The problem I have as regards to plumbing in the coolant system to the inlet manifold is that the engine is a 2.1 DJ so where would the pipes connect to on a DG in comparison?

Sorry for all the questions.

Sorry just seen yesterdays posts, I am running the DG distributor (single vac) and standard DG timing on the MV (5 degrees BTDC @900RPM vacuum disconnected and plugged to set) I do have the manifold preheater connected and the engine will happily drive in tickover on the flat and pull away with no hesitation or flat spot, it does this on both LPG and petrol. The main issue that I have had in the past is the vacuum advance pipe being larger on the Weber than the distributor and needing an adapter (now sorted having turned my own) the plastic ones tend to split the pipe.

Top man weimarbus,

I will get this manifold connected up to the coolant supply.
looks like I need to run the hose as follows:
• Thermostat housing to the LHS of manifold
• RHS of manifold to choke.
• Other side of choke to bleed rail.

Is this how your Weber is set up?

And out of interest did you connect the electrical manifold heater up also?

If you have any pictures of these areas I would like to see them.

Cheers.

I connected up the aforementioned manifold coolant hoses and can confirm this has solved the hesitation issues I had at low rpm.
I also connected up electrical heater underneath the carburettor with a thermoswitch and relay to help with the cold starting.
Finally getting there!