E30 316 with Weber runs rough and stalls

[janneman]

Hi everyone,

I'm the proud owner of an almost original BMW 316 which I inherited from my grandfather. The car mostly has run great after I fixed some problems caused by not being driven fot a while. Three years ago I had some problems with the Pierburg carburetor so I installed a new Weber 32/34 DMTL kit. Cat has run flawless ever since.

I use the car mostly to go on a holiday with my girlfriend every summer, and I decided to change some older parts in advance. The following was replaced:

- rotor, distributor cap, spark plugs and HT leads
- engine mounts
- rubber base for the carburetor on the inlet manifold

A few days before leaving (I did not realise it at that time) some slight misfire started, manifesting itself by vibrations at around 80 km/h. Faster or slower were less of a problem. We left Amsterdam for our holiday in Poland with no problems and close to the German border the car suddenly lost power. I could only drive around 30km/h over the shoulder and called the Dutch roadside assistance.

A very capable mechanic with a lot of knowledge of the 316 specifically arrived and together we tested a lot of things. Fuel pump seemed to be working but we installed an electric one to be sure, still the same problem. Ignition seemed to be ok too. He replaced the inline fuel filter but could not help me any further but instructed me to check the float valve. The car would idle well and rev when not in gear, but would stall after accelerating for two seconds, trying to push it further would stall the engine completely.

So I removed the carburetor top and checked the float valve but could not find anything. It is one of the brass type without viton and has a slight shiny ring around the contact point, but does not seem to be recessed.

For whatever reason the car decided to run after assembly like it should. Happy we continued our Journey, slept somewhere in Germany and left for Poland the next morning. Close to Berlin exactly the same thing happened again. So I again pulled the carburetor top while parked on the shoulder, checked the float and needle, assembled it and the car was fine again, but now with less power and more misfire. This happened three more times that day...

We later found that it will not occur when driving slower, 90km/h max. The car gradually lost power during our holiday, but regained some while driving back home for whatever reason.

What is very interesting is that the inline fuel filter seems to be almost empty all the time, really only a tiny puddle of fuel barely touching the filter on the inlet side, and also air in the outlet side. Removing the air does not help, it will come back after a while. When sitting for a few hours there will be more fuel in the filter. The car also seems to run better when cold.

What I have checked:

- Fuel lines are not clogged, from the pump inlet I can blow through the line with my mouth, and also from the pick up. Pick up itself is fine and no dirt in the tank or pickup filter.
- fuel pump really is ok, it will pump a bottle full in a few seconds of starting, I opened the pump and the membrane is fine, as are the two internal valves. Pump was replaced about 6 years ago. I did however see that the push rod seems to be eating the bushing, a lot of metal shaving and play in the rod/bushing.
- ignition coil has a resistance of 1.1Ohm and 8.83kOhm which seems to be normal. The coil does however get very hot while driving, too hot to touch.
- spark plug color is normal.
- fuel consumption is normal.
- I can blow through the vent line near the left rear tire and I do not hear hissing when removing the fuel cap.
- no dirt in carb fuel filter and no (visible) dirt in the carb itself. Jets are clean. I sprayed through various openings of the carb with brake cleaner with no effect.
- I once let the car rest for 45 minutes to cool down when it stalled and after that time the problem was still there, only removing thre carburetor top seems to work

I really can't figure this one out and it kind of ruined our holiday. I also can not figure out if it is the ignition or the carb. The car also sometimes runs better for a while and then misfires a lot again. Driving slower than 70km/h mostly seems normal, but sometimes it also misfires then. Any tips would be of great help. Thanks!

[fixedwheelnut]

Sounds like fuel starvation, is the tank clean,? sometimes the pick up can look clean by the time you get it out because the fuel flow has stopped the dirt falls away from the pick up, as fuel flows again it can get sucked up against the pick up clogging it again.

A similar thing can happen on the air intake with plastic bags or crisp packets inside the air intake.

[martauto]

Welcome to the zone mate .
My Weber was stripped and cleaned (not by me) and the car has run lovely ever since but when I replaced the ignition electrics I found some joker had put the dizzy cap on 180 degrees out !!!!
My fuel filter does not fill up either but Im tempted for you to look at the carb seating again just to make sure its all good and also the cam cover venting will have a part to play.
By the way, pics of the car would be nice as well

Mart.

[janneman]

The tank is almost clean internally. I see some specs of dirt in it on the bottom when I remove the pick-up, but not enough to close the large filter on the pickup. Suction would also not be enough from the small fuel consumption and one way fuel line I think. There is no rust whatsoever in the tank.

I'll replace the new rotor, cap and HT leads with the old ones tomorrow as a test.

I did however find that there is a lot of radial play on the primary throttle shaft, probably close to 0.5mm. I don't know if this can be of significance for cruising at 80km/h. Idle is rougher than it used to be but it still idles at 900rpm.

I filled the tank today and the fuel consumption is very low, probably because of my 90km/h cruising, but I got 1 liter for 13.5km now. This really puzzles me, I would think that fuel consumtion would go up with the rough running. Could a valve maybe became have lost clearance? I checked them a year ago and they all had exactly the setting I gave them a few years before that, but maybe something happened there

I'll post some pics later! The colour is 'lapisblau'. I still have to work on a bit of rust, the rear chrome bumoer had been replaced because they were conpletely rotted. The only optical modification I did is fitting a set of BMW honeycomb 14" wheels instead of the stock steel ones

[martauto]

I think that is a great idea to change back to a "known" working ignition system then you can take it from there.

Mart.

[janneman]

My fuel filter does not fill up either but Im tempted for you to look at the carb seating again just to make sure its all good and also the cam cover venting will have a part to play.

Mart.

What do you mean by carb seating? And how much fuel is in your inline filter? About half? Because I now have maybe 1/10 full, really only a tiny bit that does not even cover the whole bottom of the horizontal filter. I'll probably bypass the filter as a test

[janneman]

So I have a few updates:

Swapped the new rotor, distributor cap and HT leads for the old ones. It did not change much, also the car is now empty and when the problems started I had a lot of extra weight in the car, so no wonder the car feels faster now. I should first have done a test drive with the new parts as a reference, I'll do that later.

The fuel filter was sucked empty again, but the car keeps running. What is interesting is that when I park the car for 30 minutes and start her again she will idle slowly, and the fuel filter will be dry. However, after a minute or so the fuel filter will suddenly pulse full of fuel, after which idle will increase. Could this be done by a sticky float needle that will only open when the fuel level gets way too low? I'll set the float height later, but it should be ok since I never touched it.

Another interesting fact is that I checked the vacuum advance while on the holiday, and I can see the pulse generator shift when I suck on the vacuum line. The vacuum is also maintained for a while, so the membrane seems to be ok. However, always when I removed the vacuum line to set the ignition timing the idle speed would instantly drop by a few hundred, probably because of the air leak through the line. When I disconnect the line now idle stays exactly the same, I can't hear a single thing change when plugging the line in or out. I can blow through the line in the carburettor so it does not seem to be plugged, but there does not seem to be a vacuum either. When I block the line with my finger and rev the engine I do however feel some sucking. Could it maybe be partially blocked in the carburettor? I think no good or changing vacuum advance could maybe create my problems since they are mostly encountered with high rpm/butterfly valve almost closed.

Lastly, there really is a lot of radial play around the throttle shaft, at the side where the throttle cable is connected. Maybe even 0.5mm but its hard to measure with the carb mounted. When I spray there with brake cleaner the car almost dies after two seconds.

I have to say that I am a bit disappointed in the Weber now. The carb was new and maybe has done 10.000 km...

[martauto]

10 K is nothing at all for the weber as they are super reliable and durable too.
I was referring to the "gasket" between the carb and manifold which would give you problems if not seated properly.

Mart.

[30316]

10 K is nothing at all for the weber as they are super reliable and durable too.
I was referring to the "gasket" between the carb and manifold which would give you problems if not seated properly.

Mart.

This reminds me when my car was relatively young in early 90s when my car wasn’t running quite right and I took it to the main dealer. They replaced the rubber gasket between manifold and the carb as they said the gasket can become porous and so draw air. This did cure the problem. The carb in this case was the Pierberg.

[janneman]

I actually replaced that manifold rubber as well because the old one started cracking on the outside, about a month ago. I'll check it for leaks when I remove the carburetor.

Is it normal to have that much play in the throttle shaft? There also is an obvious vacuum leak, maybe the seal and/or bushing failed. It's hard to see because the throttle springs and all kinds of links are around it, so I'll have to take it apart to check

[30316]

I actually replaced that manifold rubber as well because the old one started cracking on the outside, about a month ago. I'll check it for leaks when I remove the carburetor.

Is it normal to have that much play in the throttle shaft? There also is an obvious vacuum leak, maybe the seal and/or bushing failed. It's hard to see because the throttle springs and all kinds of links are around it, so I'll have to take it apart to check

I don't think it is normal to have any noticeable play in the throttle shaft. You can try putting some grease around the shaft to see if it makes any difference temporarily.

Carburetor repairers normally either re-bush or drill the body out and fit a small bearing to take the play out in an excessively worn out shaft housing.

I still think you may have a restricted fuel supply.

[janneman]

I don't think it is normal to have any noticeable play in the throttle shaft. You can try putting some grease around the shaft to see if it makes any difference temporarily.

Carburetor repairers normally either re-bush or drill the body out and fit a small bearing to take the play out in an excessively worn out shaft housing.

I still think you may have a restricted fuel supply.

From what I saw on exploded views the Weber 32 34 dmtl has small teflon plates wrapped around the shafts acting as a bushing, and actual rubber seals as well. So if I have a leak there the seal must have failed, and there probably is something wrong with the bushing as well.

As for the restricted fuel supply, I think it is sufficient if I can blow through the whole line from both sides with my mouth (even lungs, which has lower pressure I guess). The fuel pump will also fill an empty fuel bowl in a few seconds of starting, or pump a wine bottle full in 10-20 seconds of starting. But I plan on trying to run the car with a new (temporary) rubber fuel line between pickup (which I checked and is ok) and pump to see if it makes any difference

Thanks to you all for the help by the way! This really is a complex one and I can use all the help I can get, since the 316 is one of the rarest e30 so there is not a lot of information online

[30316]

With Weber it should be fairly easy compared to the original Pierberg carb with its associated electrical gizmos and the ecu to contend with. I am not sure which part of the world you are as some countries do use a higher amount of ethanol. With higher ethanol content it may have damaged the carb in some way or the rubber fuel pipes may have become porous. Though BMW do say all their cars are compatible with E10 but Weber is not original fitment.

[martauto]

It sounds like you are more than capable of stripping down a Weber (I`m not ) so I would do just that but before you do, try and get in touch with Weber and see if they can help.
316 Baur now thats rare.lol
Mart.

[janneman]

I always use 98 octane fuel with 0-5% ethanol so that should not be a problem.

Today I got myself 5 metres of transparant hose and made a temporary new fuel line directly to the pump without the inline filter. Made no difference unfortunately. The car once almost died on me while going to get the new hose, would almost not idle anymore except when using a bit of choke.

I immediately pulled over and removed the airfilter lid. When depressing the float through an opening on top the car would temporarely run faster, but also start leaking into the venturis. So I don't think its an lack of fuel supply but rather an excess of air. I really suspect the vacuum leak on the throttle spindle, maybe the seal is loose on the spindle and sometimes creates an air leak, I really don't know. It's also a bit different than before, because it first would create a serious lack of power but would idle well.

I'm done with it for today, tomorrow or monday I'll remove the carburetor and see what I can find.

Oh by the way, when blowing through the new fuel line the tank will pressurise somehow, the cap will hiss when I remove it. How fast should the tank ventilation remove pressure/vacuum? I never heard the tank cap hiss when removing it, so maybe blowing hard into the tank is just too much. Driving without the cap does not seem to make a difference

[30316]

Your last info suggests the vent pipe may be blocked. When you remove the filler cap it should not de pressurise. I do not know Webber dmtl carb. I have experience of the Pierberg.

[janneman]

Yesterday I drove a while without the fuel cap as a test and it stalled again, so venting is not the issue.

I removed the carburetor and immediately saw what probably is the issue. My new manifold rubber failed, on both the top and bottom there are some rubber 'ridges' that act as o rings to create a good seal. With the carburetor removed but the aluminium adapter plate still in place on top of the rubber I could see these o rings partially sticking out into the manifold. They must have been too weak and get sucked into the manifold because of the vacuum I suppose. This was the case on both the top and bottom seal of the rubber, the bottom has two concentric sets of these rings and the innermost set of the bottom actually is partially ripped loose of the rubber with a few parts missing, they went into the engine.

Great quality those febi manifold rubbers, it held for maybe one month/1000km. This is the second time a new (rubber) part failed on me instantly, a few weeks ago my new Topran engine mounts became soft and 'collapsed'. The one on the exhaust side sagged so much that the radiator fan started hitting the bottom of the plastic cover of the radiator. Guess I have to swap to using only BMW parts, but that's a bit expensive for a broke student. Maybe I'll give Corteco a try.

I still disassembled the carburetor and found that the throttle shaft seals indeed have small air leaks around them. They seem to have become hard and became damaged by the wobble in the shafts. It's not dramatic and not the cause of my issue, but I plan to fix it in the near future. Measurements of the seals show an outer diameter of 12mm and inner of 8mm. They sell 2RS ball bearings in this size, so I plan to remove the seals and press these bearings in instead. The 2RS will create a good seal and there will be no wobble left. Unfortunately nobody has them on stock near me so I'll order them online and install them later.

Another question, I want to set the float height correctly, but my DMTL has floats which are not flat, but have a bump in the middle on top. https://fastroadcars.co.uk/store/index. ... uct_id=472 like these. So which surface do I need to use for setting the float height? I can only find instructions for floats that are completely flat on top, nothing for this type of float. Personally I would think the top of the bump, it is located in the middle and round, so I think it would be a better measurement surface for when the float is not completely level. If I was a Weber engineer that would be my choice, but I am not sure.

[martauto]

I was referring to the "gasket" between the carb and manifold which would give you problems if not seated properly.

Mart.

Have you run the car since sorting out this issue ?

Mart.

[janneman]

Another update

I spent most of the last two days troubleshooting the car. I installed the rubber carburetor flange with an generous amount of sealant on both sides, not as a permanent solution but to test. It did not help unfortunately. After that I disassembled the distributor almost completely because the pulse generator was touching the impulse wheel. Did also not help.

During tests I concluded that the issue at the moment is:

- slight stumbling when idling or driving at a constant speed. Can be felt in the car itself while driving, like an uneven road a bit
- A slight rumbling sound from the exhaust system (best hearable at the first silencer), a bit like thunder really far away
- It gets worse when warm with a very slight loss of power

No stalling issues yet, but they almost exclusively happened when driving for a while on the highway, which I did not do. The car is actually acceptable to drive at the moment, but I am afraid that the stumbling is connected to the sudden stalls sometimes, and I would rather have it fixed.

Do you guys use an pressure regulator with your Weber? Because I don't, and there is visible wear on the float needle. I heard that the Weber wants a max pressure of 4 psi, while the 316 fuel pump should be replaced when not giving a pressure of 7.5psi at idle.

And what resistance is normal on an ignition coil? I have 0.9 ohm and 7.6kOhm when cold and 1.0 Ohm and 8.4kOhm when warm.

This really is driving me mad, I spent so much time troubleshooting and I really can't find anything. It is such a simple system and I have checked everything as far as I know.