bmwe21.net forums

Despite the long saga getting my Weber carb & fuel system to work as they should I am now faced with a new issue.

The car starts fine & idles ok if a little lumpily. At speed (60mph +) it's fine but low speed pick up is pretty sluggish - one big flatspot really. Let the revs drop too fast (sudden braking at a junction) & the engine will die.

I suspect an air leak or similar. All fuel lines, filters etc have been replaced. I don't know the age of the carb (or if it's even jetted correctly) so it may be a 'split diaphram' or similar. It should be a DGMS but there doesn't appear to be any identification on it. Any suggestions on what I should look for?

Should I try & overhaul the carb myself or is it best to send it off for a professional job?

Hi Andy,

I bought a second-hand DGAS and went through 18months of tinkering before I got it to run nicely - even then it is not as smooth as the original solex 4A1. Although IMO the weber is easier to tinker with. I replaced the following;

- idle jets to 60s
- main jets to 155s
- replaced spindle bearings (nylon sleaves) with sealed micro bearings
- eliminated the anti-stall valve vacuum - that over fuelled on run down and used to force the car to stall
- blanked the emission tube
- junked the fuel pressure return valve

My main problem was with vacuum leaks; I eventually bought a new insulator block and gaskets and with a smear of Hylomar gasket seal, BINGO!

I suffered poor acceleration, remedied with 155 mains - I can't recommend fitting a rebuild kit more strongly - also IMO put an inline fuel filter (hengst) and ditch the filter in the carb; when you tighten it into position it can twist and then cause a blockage.

I hope the above is of use.

Ta, Simon.

Thanks for the reply Simon.

My car has a manual choke which I guess makes it a DGMS. I'll make a note of your jet sizes as I have no idea what's in there at the moment. I think I need to check for air leaks.

I have two in-line filters - the oem canister filter going into the fuel pump & a clear plastic in-line filter between pump & carb.

I forgot to push the choke fully in on the way home on Friday The the flat spot disappeared & the car drove like a dream but I'm not sure what that's telling me. It has been suggested that the idle valve may be blocked so maybe the choke was compensating for that.

I'm trying to track down a trouble-shooting guide or a how-to-rebuild on the net without much luck.

Can you suggest what simple first steps I should take before tearing it all apart?

Hi Andy,

Without tearing it off, you can check the jets first. Open the cover, turn out the jets and check them. If it is a DGV, then check the diaphragm of the power valve (triangular inside), then check the diaphragm of the acceleration pump (outside). Hold them against a bright LED lamp. Then you maybe will see the problem. The diaphragms should be smooth and flexible.
Maybe you can post a picture of the carb, then we can see which type it is. DGV has also a manual chocke.
Murat

I didn't get time today but I'll check for air leaks first.

Here's the carb (there's no obvious identification on the tag but I believe it to be a DGMS).



Here's the manual choke









IIRC someone told me you didn't need the water heating to the manifold with a Weber :-



I hadn't noticed how dirty the carb body was - I need to lay in a good supply of carb cleaner.

Hi Andy,

Ok, you have the same carb as me - good start. Suggesting your car ran better with the choke points to too much air; I recon in the first instance one of the diaphragms has rotted and is leaking air, your spindle bearings are also probably leaking too - a service kit from fast road cars is probably a good start. If your car ran ok in the past you probably don't need to change the jets, either in the idle or main circuit. But if it has always been a bit iffy then upping the mains by a step or two (0.05 to 0.10 - i.e. 45 to 50 is one step), if you need to back the idle screws out more than 1.5 to 2 turns it would be worth going up a step or two. I have the set up instructions but they are very idealistic and based on a motor that probably has fewer miles that ours! I can copy them and e-mail - ping me a pm with your mail address. With regard to the spindle bearings I would recommend purchasing these http://www.ebay.co.uk/itm/Throttle-shaf ... _CyeXzZ83w, slot the nylon bushes in first and pop the sealed unit in after with a fine smear of grease and that should stop leaks at really the only weak point in the carb.

You'll need to give the carb a good thorough clean when you strip it down - take your time, I stripped mine down so many time chasing leaks that I could strip it down in 10mins or so; it is a really simple piece of kit.

You mention you have two filters, you may also have a third lurking in the bolt that sits under the front of the carb where the fuel in / out line are positioned. If you have filter protection I would remove this as they are notorious for blocking and causing poor power.

You have my jet sizes, my car is a standard 320/6 with 135k, it burns very little oil between oil changes and I have set the valves a little on the tight side, so that should give you an idea of parameters that may influence how your car may run.

I'll keep an out & BOL!

Simon.

Thanks Simon.

Mileage is currently showing 141,000 but it did have a replacement engine some time around 2004/130k miles. Mileage on the replacement motor is unknown but it doesn't seem to use any oil or water. There's a bit of oil mist here & there but nothing to get too excited about.

I have no info on when the Weber was fitted although the monkey that did the job got the inlet & outlet pipes mixed up! I've no idea how it even ran! All sorted now with new fuel hoses & pipes throughout. Fuel currently goes though the (oem?) filter into the pump (with clean filter) then through a plastic see-through filter to the carb (then back to the tank). I thus don't have much idea on whether the car was running right before the current malady! I couldn't get it to idle without the idle speed screw cracked open a little bit. The idle screws certainly needed to be turned out more than a turn & a half. This all makes me think the carb is leaking air like Apollo 13.

I intend to replace the oem filter & have considered fitting a Malpassi Filter King filter/regulator between the pump & carb. A rebuild kit is essential really as so many other rubber bits have disintegrated on me it's a given that a diaphram has split. Those spindle bearing look like a very good idea. Anywhere you can recommend to get the rest of the overhaul kit?

I'll worry about jet sizes once I have the rest ship-shape.

Hi Andy,

Service / rebuild kit; http://www.ebay.co.uk/itm/WEBER-38-DGAS ... GKqy23-Tpg, Anthony (proprietor) is really helpful and stocks EVERYTHING (apart from the needle bearings - BTW, they are fantastic!)

I have got a pdf of the full service document which is really helpful - lots of piccies and explanation, pm me your e-mail.....

Once you have had time to digest, there are a number of bits of the carb which are just not needed; the anti stall is for Automatic gearbox cars and causes the stalling issue you refer to - block off the vacuum and you should see an improvement. Also the emission tube at the front of the carb (behind the quadrant mechanism) is a source of un-metered air, so should be blocked too.

If you are placing an order with FRC, I would get jets too so you're not pulling it apart again...

Simon.

Just make sure that when you are adjusting the mixture, you are adjusting the two very small screws either side at the base of the weber, NOT the two larger brass screws which are higher up the carb body - those are actually the idle jet screws, opening them has a misleading affect on the idle speed but in fact all that does is allow air in and will cause poor running when actually driving, stalling etc.

Apologies if this is obvious to you already, but worth checking as it had me going mad at first when I installed mine

The idle jet screws should be closed.




P.S. I have the water choke on my DGAS and I hate it, can't get it set right, could you please show me how the manual choke on yours has been routed in the engine bay to the cab, and where the handle is mounted in the cab also please?? Thanks.

Dave

Also, I will add that I found using the weber with the stock filter assembly a nightmare, since I did away with that and added a K&N it runs a lot better, you need to add a cylinder head breather filter also but that stops any gunk being dumped into the carb!

davidvincent wrote:I have the water choke on my DGAS and I hate it, can't get it set right, could you please show me how the manual choke on yours has been routed in the engine bay to the cab, and where the handle is mounted in the cab also please??

Sorry for the delay - got side-tracked buying another car





The choke mounts under the dash (lower dash cover removed)


Hope this helps.

Thanks Andy - that's really helpful, much appreciated!

How did you get on with your carb?

Dave

I haven't had a chance to do anything with the carb yet. I've got the recommended service kit & a set of new spindle bushes. The Baur's going into the bodyshop on the 23rd to get a couple of small holes welded up then it'll be SORN'd until the spring. I'll do the carb over the winter.

Simon has recommended I find somewhere with a Chem-Dip tank to remove the varnish etc. Must be somewhere in the Newcastle area otherwise I'll have to get a bucket & do it myself. Frost Automotive will probably sell something to do the job.

Ok - update on the carb. I eventually bottled out of doing the job myself & farmed it out for refurb by Weber Carb Reconditioning Services. He used the new gasket set & spindles I had already purchased.





I also found a split on the back side of the vacuum pipe to the distributor - that wouldn't have helped the advance/retard function.

I tried setting the carb up as per the various guides on the net but eventually set both idle jets to 2.5 turns out then screwed both back in 1 turn. This seems to give good drivability at engine speeds over 2,000rpm. There's a hesitation/flat spot comining off a closed throttle below 2,000rpm. At first I thought it was a mechanical problem - sticky throttle mechanism etc but it's all lubed up and seems ok moving by hand.

It seems the transition between idle & main is the problem. After a good hard run I found revs would drop at junctions. It would usually catch itself & bring the idle speed back up to the 800/900rpm idle but occasionally it stalls. Does this mean my idle and/or main jets are too small? Simon [mendipdriver] suggested I go up a size. As far as I know, this is the official Weber replacement for the E21 320/6 so jet sizes will be as recommended by Weber.

I realise I really need to find a rolling road and carb-savvy technician to do the job properly.

Last update.

The idle jets were 55's so I fitted a set of 60's. Big difference. Car now idles easily & transitions without problems. Thanks to Simon for his help.

I put a new choke cable on too. Apparently setting up the cable tension on these is critical or it will kink. Full choke seems to make the flaps snap open under spring pressure so closing the choke (ie. opening the flaps) has to overcome the spring pressure. Seems a daft design.