Club 80-90 Forums

Ah yes, I've seen a few carbs on ebay with those canisters. I guess that takes the pressure off the float valve. Now I look, there seem to be quite a few configurations that don't have the return spigot. I have Pierburg's exploded diagram of the LT's carb, and there's no sign of a vapour canister for this particular model (or a return spigot). Oddly though, the diagram does show an enrichment nozzle, but the one I have has definitely never had one - the casting isn't drilled for it.

I'll probably convert the carb over to the T25 configuration, block off the vacuum nozzles that I don't need and give it a whirl.

Here it is all dressed up in T25 parts, ready for a trial run on my DG. My donor carb came in very handy. I had to change the throttle spindle over, to get rid of the bracket on one end of the LT version - the spindle on the LT isn't exactly the same as the T25 version. I had to add the throttle body heater from my donor carb. I had to make a couple of vacuum bungs - there's an extra nozzle on the choke pull-down unit, and the extra nozzle in the top plate. The extra nozzle by the heater (bottom of the first and third photos) I just left connected up to its neighbour with a t-piece, as it had been on the LT.

In changing over the throttle spindle I noticed that the butterfly on the primary venturi has a small hole in it on the T25 carb but doesn't on the LT carb. I kept the LT version, without the hole, as I'm assuming the complete carb works well as it is.

I fitted the carb to my DG this morning. After transferring over the relevant parts from my donor T25 carb it was an easy swap. Only the blanked off and tied up fuel return pipe gives it away.



One small issue with fitting: the toe of the accelerator pump lever, where it rides on the cam at the end of the throttle spindle, was just touching the inlet manifold, so the cam was getting stuck behind the lever at full throttle - with the result that the throttle was sticking open. That's a bit scary on the road! I swapped the pump lever for the one on my original carb - on closer inspection this seems to have been trimmed down at the very end - you can just see that in the second photo below.




I set the idle mixture crudely by ear - wound it in till the revs started to drop and then wound it out half a turn. With the new carb the engine runs smooth and even. Just like it did before in fact. I'm hard-pressed to tell any difference on the road. Maaaybe there's a little more torque at low revs, but I wouldn't swear to it. At 70mph there's still plenty of pedal left, but then there was before too. Certainly there doesn't seem to be any issue with the lack of the full load enrichment nozzle that I can detect from the driver's seat. Maybe a gas analyser might show a difference. The exhaust doesn't smell any different at idle, but the idle mixture is only a small part of the story.

So one way to interpret this is that the normal carb is big enough for the 1.9, and the LT carb is even bigger enough. In other words, it's extra capacity is not needed for the 1.9, but maybe it has enough margin to supply a 2.1 as well. But then maybe the original carb does too.

I think I'll fill up with petrol and run this carb for a week or two to monitor fuel consumption.

After pootling around on local roads for a few days, I've got a better feel for the difference the LT's carb has made. It definitely pulls more smoothly and more willingly from very low revs. I can pull off in second for instance and it takes much less clutch slipping. I haven't been on any more open roads at high speeds, but across the normal rev range it seems to pull a lot more smoothly. Having serviced my carb and had the mixture set only a year or two ago I always felt it was running well, with no flat spots etc, but it's noticeably smoother now, especially pulling away from rest.

Logically I think it can only be doing this by throwing more fuel down the pipes, so I'm expecting heavier fuel consumption. Half in anticipation of this I'm making a conscious effort to use less throttle, and I'm using the extra go at low revs to help with changing up sooner. Maybe this is contributing to my impression that it's altogether smoother.

It's possible this is all in my mind, and the test will be to put the original carb back on, now I know what I think I'm looking for. I don't know that I want to bother with that though, just for the proper scientific principle, since it's running so well with the new carb.

Cheers for the update Chris has been an interesting read. Do you have a rev counter fitted & if so do you know the rev range for top gear at say 50 mph compared to your old carb? Just wondered if it was any different.

I don't have a rev counter, but I'm not sure I understand the question - the engine speed is related to road speed via the gearbox and the wheels, so the carb won't have changed anything. If you mean what rev range am I using now, compared to with the original carb, then I agree that would be interesting to know. But I've only ever had the vaguest idea what revs I'm using.

Hi Chris, sorry mate I typed that out on my phone whilst on a packed train home (that's my excuse anyway) - yeah it was the latter part re the rev range. Put a rev counter on your Xmas list

This carb really does need some data from a rolling rd.
If it can deliver us from the hill misery I will chip in something for the cost of a test on a dyno

Certainly would be interesting - I'm gonna get my Weber dyno'd one day so will put the stats up when done. I think it pulls really well and seems pretty reasonable when going uphill for such a little carb on a big vehicle. That said I do drive like an old f4rt

Yes, that's an interesting idea. I think I'll save that for when the 2.1 is in and run in, since the result will be of more interest to me personally. I could take both carbs along for a direct comparison, and that way the fact that I'll have Ian's cam and a Speedshop exhaust shouldn't really matter - it's the comparison between the carbs that will be interesting.

I've got no idea where I'd go for a rolling road test, but I'll start looking into it.

Not sure how far you are away from this chap Chris, but he has good reviews:

http://www.ssvc.org.uk/phpbb/viewtopic.php?t=55804" onclick="window.open(this.href);return false;

That's not far away at all. And he's experienced with VW vans too. Sounds like he's worth contacting, thank you.

I'm getting a good feeling about Peter Burgess from 300CE's link above. We've already had a bit of an email exchange this morning. For quite a reasonable sum he'll measure both carbs and re-jet one or the other (drilling and/or soldering as necessary) to get the best setup. Definitely something for next year when the new engine goes in.

I've booked a dyno session with Peter Burgess. To his credit he's adamant that it's not really useful to just 'measure' a new carb without re-jetting and adjusting it, but I just want to get an initial idea how the DG performs, both with the stock carb and with the bolt-on LT carb. If nothing else, the stock result will be something I can use if I decide to sell the DG. It'll also tell me if my impression of the improvement at low rpm is anything more than wishful thinking.

Once the DJ is in I'll take him up on his re-jetting/tuning service to get the best from whichever carb he thinks has the most potential. After that second visit I should have a full set of measurements:
- DG with stock carb
- DG with bolt-on LT carb
- DJ with stock DG carb
- DJ with bolt-on LT carb
- DJ with tuned LT carb

As a lot of us have 2.1 carbed engines, with the standard pierburg, I for one would be interested in any pierburg adjustments to enhance the 2.1