Early 1.9 to 2.1 conversion - stop me if I'm being stupid!

[CJH]

I'm inclined to agree, but an air leak somewhere in the manifold would affect both carbs (manifold to head gaskets, hedgehog seal, brake servo hose, even the little core plug could have sprung a leak - this is a secondhand manifold that I grit blasted to clean it up).

I can see the actuator arm moving inside the distributor when I apply a vacuum pump - I didn't notice whether the rotor arm moved or not, should it? This is a rebuilt distributor, with a new correct vacuum unit, which I tested briefly on the DG. I suppose it's possible the actuator has become detached inside.

Yes, the idle bypass seems to work - it clicks when I connect the live cable.

I'd love to check and adjust the timing, but I need it running to do that accurately.

E D I T: Just a thought - the LT carb ran very rich on the DG. Chances are it's still a bit rich on the DJ, so that may be the difference between the LT carb coping with an air leak and the DG carb not.

[itchyfeet]

I can see the actuator arm moving inside the distributor when I apply a vacuum pump - I didn't notice whether the rotor arm moved or not, should it? 

no rotor arm is fixed to drive gear, the vacuum moves the mechaism with the hall sender so you cant see movement without removing the dust cover.

[CJH]

no rotor arm is fixed to drive gear, the vacuum moves the mechaism with the hall sender so you cant see movement without removing the dust cover.

Yeah, I discovered that this evening. I compared what happens with another distributor, and realised that the actuator arm had become detached from that hall sensor base plate. I took it out, took it apart, and reattached the arm. I'm going to do that again I think, because the connection doesn't seem very positive - it's just a small disc on the underside of the baseplate that locates in a hole in the actuator arm. It seems like it could easily drop out again.

I also stripped and checked the LT carb, and fitted all the new bits from the refurb kit. The choke adjustment was way off, would never have set the fast idle, and would have cancelled it completely with the first use of the throttle, and there was a bent spring (that's where a 'parts' carb comes in handy) but everything else seemed ok. So the only issue I'm aware of was those loose screws holding the two body halves together, and actually that's not as bad as it sounds because the three nuts that hold the carb to the manifold will do much of the job of those screws. I didn't find any other leaks or problems with the intake. The core plug in the manifold is for the water circuit, not the airways.

So two possible faults then - the disconnected vacuum advance arm, and a possible air leak between the carb body halves. Anyway, with it all adjusted and reassembled it works! After I remembered that it needs the idle cut-off valve connected to idle below about 1400rpm (and boy does it idle rough even above that speed without it) , I was able to set the timing (10º BTDC now) and the idle speed, and it's fabulous! I'm puzzled why it felt better yesterday after I fixed the split vacuum advance hose - maybe it was just wishful thinking - because with the actuator arm disconnected it can't have made any difference. I suspect my gradually worsening problem yesterday was a combination of that arm disconnecting at some point, and the carb leak getting worse. But I'm not convinced.

Anyway, on the road it's smooth, clean, lively and pulls like a train! Much better than it's ever been since I've had the engine running, so one or both of those problems must have been there since the start - it's surprising that it ran at all, but it did, and it felt quite good.

Now I'd like another day in the peak district to make the most of it!

[itchyfeet]

you set timing without vac conneced so the change it gives could not have been the only problem at idle, it should still idle although revs will be lower, I wonder if the hall sender plate is free to move much more without the vac arm connected.

[CJH]

Yes, that's true. And I suspect you're right that the actuator arm does limit the movement of the sender plate. So either the actuator arm was never attached, and the sender plate drifted around during my journey, resulting in worse and worse performance, or perhaps the arm became detached while it was under vacuum, leaving the plate in the wrong position. Either possibility would be enough to explain the inability to idle, without the need to blame an air leak.

[bigherb]

Yeah, I discovered that this evening. I compared what happens with another distributor, and realised that the actuator arm had become detached from that hall sensor base plate. I took it out, took it apart, and reattached the arm. I'm going to do that again I think, because the connection doesn't seem very positive - it's just a small disc on the underside of the baseplate that locates in a hole in the actuator arm. It seems like it could easily drop out again.

The vacuum arm should be retained by a lip on the baseplate. When replacing the vac unit you have to make sure the arm does not drop off the spigot and slide the other side of the lip.

This one had shown by the witness marks on the baseplate
Shown in the disconnect position


This how it would be when the vac is screwed on.

[CJH]

Ah yes, of course, thank you. So once it's on and working it can't come off. Definitely looks like I must have made a mistake when I first assembled it then. It's amazing that the poor thing ran at all, but actually I was reasonably happy with it at first. There's a world of difference now though, now that the vacuum advance is working properly.

[itchyfeet]

CJH please can you remind viewers exactly what LTcarb you have, there was detail some where but can't find it?
Interested to see how the rejetting goes too.

thanks

LTCarb (one word as you can't search on lt and carb gives too many results)

[CJH]

It's a 073129015A - discussion here. It's from a 2.4LT, 1986 to 1992. It differs from the DG carb in that the primary venturi is 24mm diameter, rather than 22mm. The jet sizes are different too. According to the Haynes carburettor book it's the only variant that's bigger than the DG carb. When I first looked at it I thought the ~10% increase in the venturi diameter was a perfect fit for the ~10% increase in engine capacity of the 2.1 over the 1.9. But of course that 10% increase in the venturi diameter equates to almost 20% more area (a better match in fact for the 26% increase in capacity of the 2.4 over the 1.9).

What this means in practice I don't know - that's why I'm doing this, to find out. But my first thought is that the air speed through the LT carb on a 2.1 will be a bit slower than through a DG carb on a 1.9. I guess this means something for jetting, because I think the airspeed may affect the amount of fuel that gets pulled through. Or maybe only the vacuum pressure matters. Who knows.

When I had it tested on the rolling road there was almost no measurable difference on a DG engine. My 'seat of the pants' impression was that the LT carb was a bit smoother at very low revs (below where the rolling road started in fact), but it's incredibly difficult to compare setups I've found. The rolling road showed that it ran very rich and would need jetting to see any benefits of the larger venturi, but the guys there were quite clear that the bigger carb was the better starting point for the bigger engine.



I've got the LT carb running just-so now on the DJ (famous last words!), idle CO, cold start, accelerator pump all working as they should and it feels very good on the road. But then we know that the DG carb works well on the 2.1 too. I'm hoping the rolling road people will get back to me while I can still use up one of this year's remaining leave days to get it jetted. I got fed up with switching carbs over for a while, but I will also make sure the DG carb is running right so I can have that one jetted at the same time, for a proper comparison.

PS - these carbs show up occasionally on eBay. I've only ever seen 'new' ones, and they're not cheap. The bracketry and linkages are all a bit different from a DG carb, but they can all be swapped over.

[CJH]

I digitised that plot, in preparation for plotting the re-jetted carb(s) on the same chart for comparison.

[itchyfeet]

Looking forward to the results

[itchyfeet]

Injection throttle body vs 2e3

Ignoring the throttle spindles and flaps ( snigger) just looking at the diameter and area

Injection throttle body diameter 50mm = 1964mm2

2e3 1.9 DG diameters 22mm and 26mm = 380mm2 plus 531mm2 =911mm2
2e3 LT 2.4 diameters 24mm and 26mm =452 plus 531mm = 983mm2

This is why I'm interested to know what BHP you can get from carb on a DJ, we know what Injection can give ( if you believe VW)

20170901_155902 by Paul_Barr, on Flickr

[CJH]

That's a huge difference - it dwarfs the 10-20% difference between carbs. There must be more to this than meets the eye. I'm not suggesting that the LT carb will match the power of the injected versions, but I can't believe it would take a carb twice as big to do so.

[itchyfeet]

78 to 112 is 34 BHP increase which is 43% of 78BHP
I want to fit a DJ to my LPG DG tintop which is why I'm so interested it what it will make on carb.
an LT 2.4 makes 89 BHP is you can expect at least that I think
https://en.m.wikipedia.org/wiki/Volkswagen_LT" onclick="window.open(this.href);return false;

[CJH]

78 to 112 is 34 BHP increase which is 43% of 78BHP
I want to fit a DJ to my LPG DG tintop which is why I'm so interested it what it will make on carb.
an LT 2.4 makes 89 BHP is you can expect at least that I think
https://en.m.wikipedia.org/wiki/Volkswagen_LT" onclick="window.open(this.href);return false;

78 on the 1.9 DG to 89 on the 2.4 LT - doesn't seem much of a gain for all that extra capacity (and two extra cylinders). I'm guessing it might have been set up for gains elsewhere - torque, or fuel consumption perhaps - rather than power. The DJ feels a lot more lively than my old DG, so I'm hoping to see this borne out in the numbers. Rolling road is fully booked until late October unfortunately, but I've asked to be kept in reserve in case there's an opening next week. Fingers crossed.

I fitted my remote oil cooler today. Bit of a job getting the right angle connectors fitted to the cooler, in such a way that the spare wheel doesn't push on them. In the end I had to remove the spare wheel frame rods (again) and then refit them once the cooler was in.







I had hoped to install the cooler lower down, so as not to block so much of the radiator, but this proved impossible due to the spare wheel. In the end I'm glad I didn't, because I now realise the oil cooler is doing a huge job, and it would be counter-productive to use less of it.

First impressions, after a short high speed run (in today's warm weather): where previously I'd have seen 100º-110º oil temperature, this time the needle didn't go above 80º (as set by the Mocal thermostatic sandwich plate), and since oil pressure and oil temperature are directly related the result was a higher oil pressure. Not only that, but the water temperature needle sat 2-3mm to left of where it sat without the oil cooler.

So I have the impression that the oil cooler has taken a huge load off the cooling system, and despite partially blanking off quite a sizeable area of the radiator, the overall system temperature is much lower. Of course, the oil cooler doesn't blank off the radiator completely - air still gets through it, and I would imagine that even though that air has been warmed by the oil cooler it's still cool enough to cool the radiator a bit.

I needed to do this because I've heard the 2.1 needs to cool its oil a bit, and I'm really glad I went this route. And still no leaks!