Club 80-90 Forums

It's early, so yes, I guess I'll be measuring on just one cylinder. Is there a particular place you'd recommend?

Close to the silencer so at least you get two cylinders
I'd do 3&4 because you are more likely to get air leaks that side

I can't remember the detail of the pipe configuration, but the wiki has this diagram of the early exhaust, so I assume mine is the same.



So that means that all four cylinders remain separate until the silencer. I reckon that the single carb/long manifold configuration means that the mixture in all four cylinders is likely to be the same, so I'd guess that measuring in one will be representative. I think it'll come down to whichever cylinder gives the best access for welding the boss on in-situ. I think that's likely to be #3.

Booked into my local garage by the way.

Ah yes you are right
not ideal is it

itchyfeet wrote: not ideal is it

No - maybe I should just shove it up the tailpipe.

The gauge arrived today, so I hooked everything up and tried stuffing the sensor up the tailpipe. I got a reading, but it wasn't stable. So I'll go ahead with a boss, probably on cylinder 3.

The heater draws about an amp by the way, once it's reached a steady state. Resistance when cold is 4 ohms (-> 3A), but I'm guessing that goes up when it gets hot.

boss is cheap, you could have one welded both sides, on 1&3, fit a plug on the side not used but allows you to check both sides, gives more confidence.

That's true, I could. But I still have the air warmer gubbins around the cylinder #1 J-pipe, and it's in good condition, so that doesn't leave much space for another boss. I've actually got two different bosses on order to make sure at least one is available for Friday morning's trip to the garage, but I'll stick to fitting just one for now. After all, it's just to give me an idea how a sweetly running DG with a standard Pierburg measures. The serious stuff comes when I fit the 2.1 and start playing with the LT carb.

Well my LT carb arrived today, and unfortunately I think that's where this little experiment is going to end. It's not as similar to the DG carb as I'd hoped, and isn't going to fit without some engineering work that I can't do by myself.

Here's what it looks like:


A few obvious differences.

1) the choke is on the opposite side, and isn't operated by water temperature - it seems like it's only electrically operated. I could probably get to the bottom of that, so that wouldn't be a show-stopper.

2) The throttle cable attachment is slightly different - again, no biggie.

3) The airbox evidently attaches with a single stud, and is a bigger diameter than the one on the DG carb. I could probably source an LT airbox and adapt the air intake to suit, so again, not a show-stopper.

4) The show-stoppers for me though are the fact that the carb attaches to the inlet manifold via four studs, compared to the three of the DG carb (and even the two that look common have a different separation), and the two venturis exceed the outer dimensions of the hole in the top of the DG manifold. You can see the difference in the photo below - the manifold hole is no bigger than the two venturi holes in the DG base. I should have thought about this before - if I'd noticed that the manifold is an exact fit for the DG venturis I'd have realised that bigger venturis wouldn't fit. I reckon this could all be fixed by a capable engineering outfit - new studs, and some reworking of the manifold hole - but this isn't the simple plug and play stealth fit I was hoping for, i.e. even when it's done, it won't look like a standard DG, so if I'm looking for bigger carbs I might as well go for something tried and tested. But that wasn't the point.



So I might hang on to it and revisit it in the future, perhaps getting another manifold in to modify, and picking up an LT airbox, but I'll probably send it back to the seller (he said he'd take it back if it didn't fit). For now I'll probably just put the standard carb on.

you could make a plate adapter in place of fibre spacer out of say 6mm aluminium plate, CSK screws through plate into old stud holes in manufold and the thread new studding into tapped holes in plate, would need paper gaskets making.

a plate like that could be made with hole saw, hacksaw, drills, taps, files, not rocket science, you can buy plate on ebay or I may be able to get a bit for you

having a small bottle neck is not so much of an issue, manufold and adapter plate could be ground back (ported) a bit to smooth the flow.

Height may be your problem if the LT carb is taller.

I thought about an adapter plate, but without porting the manifold I think the benefit of the larger venturis would be somewhat lost. But the main thing for me is that it won't look like a standard DG anymore, even if I get it to fit. If the object was simply to fit a bigger carb I'd probably go for something that someone else has had good results with, like a Dellorto (or two).

Maybe this line of enquiry isn't dead after all. Today I finally got around to giving the LT carb a bit of a clean, ready to post an advert on ebay, and in the process I discovered why it won’t fit my T25 inlet manifold. It’s not the model I thought it was - the model designation was hidden under some grime. It turns out it’s a Pierburg 2B (073 129 015), and I’m looking for a 2E (073 129 015A). I bought this one from a 1987 2.4LT, and my Haynes carburettor book says the 2B was superseded by the 2E in October 1986. I guess the van this one came off was manufactured before then but not registered until 1987.

I think this means that a 2E from later 2.4LT might still work - back to trawling ebay.

Found one! On German eBay. And what a beauty - apparently it's been on a shelf for 20 years having been bought as part of a job lot from a German carburettor supplier, where it had been used to train their technicians. It's never been used.





At first sight it's a straight bolt-on replacement. But there are some differences, which may or may not be important. The biggies first.

No nozzle for full-load enrichment, secondary venturi. Maybe the bigger venturi and bigger jets make up for this, but this doesn't seem good.


No fuel return spigot! What happens to excess fuel pressure?


And some more minor issues.

An extra vacuum spigot in the top plate, and a blanking cap that needs replacing.


Another extra vacuum spigot.


An extra temperature sender on the choke heater and a different throttle cable bracket.


That punctured blanking cap again, and a missing vacuum spigot.


Something different in the throat of the primary venturi.


Nearly all of these differences can be ignored, or fixed by swapping over bits from a T25 carb. The essential difference between the carbs is the bigger primary venturi (24mm versus 22mm) and I'm working on the theory that since this is roughly 10% bigger this will be better suited to the 2.1 than the carb fitted to a 1.9, since the extra capacity is also roughly 10%. The jets are different too.

I'm tempted to swap the top plate for a T25 top plate, and perhaps swap over the jets - that way I get the jets and venturi size from a 2.4 LT, and the enrichment nozzle and fuel return spigot from a T25. But I'm floundering a bit, and would appreciate any opinions.

Trying to understand the two main differences between the LT carb and the T25 carb, namely the missing fuel return spigot and the missing full load enrichment nozzle.

Fuel return spigot:
My Haynes manual says that:

Haynes wrote:A calibrated fuel return system is provided, to ensure that relatively cool fuel is supplied to the carburettor.

So it's not to deal with excess fuel pressure - the float valve takes care of that of course. It's to allow a steady stream of fuel back to the tank, to be replenished in the float chamber by new cooler fuel from the pump. So I'm thinking that may not be such a critical issue after all. Maybe in the LT configuration they decided they could do without that, perhaps because the carburettor was located in a cooler spot (or perhaps because it used fuel so fast it didn't have time to get hot in the float chamber ). Anyway, in the T25 the carb is a long way from the hot exhausts so I'm prepared to take a risk that this cooling isn't necessary. I just have a nagging doubt that I heard somewhere that the LT had a reputation for leaking fuel from the carb, so maybe ditching the return circuit isn't a good idea.

Full load enrichment nozzle:

Haynes wrote:At full-load and high engine speeds, the velocity of air creates a depression sufficient to raise fuel from the float chamber into the base of a vertical tube. The fuel then passes through a calibrated bushing to the upper section of the secondary air intake, where it is discharged into the airstream from the full-load enrichment nozzle.

So this is to squirt more fuel in at full-load and high engine speeds. So why's it missing from the LT carb then? Maybe the 2.4 6-cylinder engine never got to high revs . Maybe the bigger main jet (135 whatevers to the T25's 110 whatevers) is such that it already gets enough fuel and doesn't need further enrichment at high revs.

This doesn't seem like such an easy difference to dismiss as the missing return spigot. Thoughts anyone? I'm tempted now to use the complete LT carb 'as is', since I think messing about with swapping jets over to effectively add the enrichment nozzle to the LT configuration might cause more problems. I'm pretty sure I've read that someone's done this swap before (Ian perhaps?), but I don't think there were any details of how these differences were addressed.

I'm also tempted to try this carb on my DG before the DJ is ready - I'm guessing that if the fuelling isn't right, the bigger jets are more likely to make for a rich mixture than a lean mixture, so am I only risking increased fuel consumption?

All of the pierburg cards I have seen without the return spigot had a vapour canister mounted on the front of the carb, it's basically a canister with 3 spigots on it , supply from pump, feed to carb, return to tank.
I would agree that it's probably best to just fit it as is and go from there.