320/4 with starting / Solex problems

[E21-driver]

Hello to all,

I am registered new here in this forum, but I am passive reader of this nice E21.net page since two years. Let me introduce myself, my name is Murat and I am from Munich, Germany. I have collected some experience over many years in classic BMWs, such as E3, E12, E21, E24, E28, E30, E36 and 02.
Currently I have a very nice E21 315, which I have upgraded with an original 320/4 engine and an original Solex DIDTA 320/4 carb which is screwing me.
Now I am working on the first starting trials, but I was not successful.
I can see that the engine wants to start and fires, but immediately it goes off and can't hold the idle. The second trial is much more difficult, it will hardly fire and needs full throttle, it fires but it doesn't start. Plugs are wet. I have the feeling that the carb overfloods the engine immediately with fuel.

I really need some advice. To make it easier for you all, please let me list some facts of the situation:

1. choke lid is working, after stepping the pedal, it closes and moves during starting, whole bimetal-choke unit is new
2. throttle flap is slightly opened in starting position, adjusted to 0,8mm distance
3. floater is tight, floater needle valve is new with original 2mm seal ring, the distance in vertical position to the carb cover is adjusted to 16.5mm, as described in the Solex repair manual
4. all vacuum hoses are new
5. the carb is completely cleaned properly, all diaphragms, sealings and o-rings are new
6. all cylinderhead valves are properly adjusted to 0,2mm
7. all timing marks are ok, the plugs fire, firing order is ok, cap and distributor rotor are new, but ignition is not fine adjusted yet (I need to run the engine first). I have kept the TSZ ingnition, cables and distributor and also the camshaft from 315 (this fits only to the 315 TSZ transistor ignition).
The ignition was running properly with the old engine. This was only 4 weeks ago.
8. the original 320/4 fuel non-return valve is not connected yet, but I have a new one here. It has one vacuum connection, one bigger 8mm connection and two smaller 6mm connections (how do I have to connect it, the bigger one is the fuel return hose ?). At the moment, the carb is connected directly to the mechanical pump. Pump changed also to 320/4 original.
9. CO and idle needles were removed out to fit new o-rings. How many turns should I screw them out. How to make the basic adjustment before starting ? How many turns out from zero ?
10. The bimetal choke unit gets 12V when ignition is turned on. Is it triggered by the 1-pole temperature sensor or by the two pole sensor ?
11. The small magnetic valve which interrupts the fuel flow is working. It clicks, when giving 12V to it.
12. The air filter pan was not connected when I tried to start, but this should not be a big issue for Solex, I guess ?
13. Which sparks should I use for the 320/4, Bosch WR8DC or WR7DC ?
14. My Solex is the early version of '76, it is the version without the 12V electric cold start valve.
15. Do I really need the vacuum valve at the front water distributor ? I have a TSZ ignition distributor with only one vacuum conenction (early ignition adjustment). For the starting process, this should not have a big influence.
16. When I opened again the lateral square pump housing, it was flooded with fuel. But fuel here is not in the right place. What could be the reason for it ?

So, I really need some advice from you E21 guys. I don't want to swap to Weber or similar, because I have already spent some money on the stock equipment. I really would appreciate if some experienced guys can comment my points. If easier for you I can also send my mobile number.
Would be great. Thanks to all in advance.
Greets
M.

[Peter V.]

Hey Welcome,

It is not easy like this but i will try.

8. no problem for this. My 320/6 has none also.
9. The CO screw you can turn about 2,5 turns out. Idle screw like two turns. This must be enough to start the engine.
10. The one pole sensor is the temperature sender for your dashboard, the two pole is for the bimetal.
15. The vacuumvalve would be no issue to start or drive the engine.
16. Here you could have the problem that there is something loose in the floatingchamber. Sometimes the metal item at the right bottomcorner is missing or came loose, mostly the little marble is gone and that is one of the "valves" of your acc.pump.

[E21-driver]

Hi Peter,

thank you for the help. I will consider your points. Especially concerning the needle screws.

And I have already checked your hint in point 16. I have heard from this issue. The metal part is tight in its' place and the little ball is inside. I can hear it. No problem in this place.

What other reasons can there be for the floating of the acceleration chamber ? Defect floater needle (it's new!) or total wrong floater level adjustment ? I have also checked against another DIDTA carb from a 316 which I have. It has also 16-18mm distance from the cover sealing to floater middle ring. Who else can help ?

[Jeroen]

With a bit of luck Peter can add some more suggestions. I'm no expert when it comes to carb but I'm just cutting in to wish you welcome here!

Perhaps you can add a little topic on you and the car(s) in the Registry one day? Enjoy the forum!

[Peter V.]

Maybe a simple question first.... Is your floatingdevice still good. It is a solid plastic thing but when there is a crack in it it could be mallfunction.

Normaly the original 2mm ring and the original floatingneedle is good. The level sounds good to me also.

Your issue with the full camber of the acc. pump. It is no problem that is it full. The bottom marble is your suction valve and when your are not using the acceleratorpump the level in this would be the same as the floating chamber. It is only when you press your pedal and the acc.pump is actually working the suction marble closes the hole to produce pressure.

[E21-driver]

Hi Jeroen,

thank you for welcoming me in this forum. As I mentioned before, I was passive reader of the BMWE21.net. Hopefully I can also help other guys here with some infos (from my side only in English of course). I will also enter the registry.

And thanks Peter,

the black plastic floater is ok, I have already tested it under water, it is tight.
Did I understand correctly: it is normal that acc. chamber is floated with fuel ? I mean the small chamber at the side where the small red diaphragm is inside ? This chamber is floated with fuel normally ? OK......then I have to read the manual again.....

Any other ideas about my problem ? I will consider everything I can get. Here in Germany, I was not so successful until today.
Murat

[Peter V.]

If you check the manual of the solex carb you will see that the floatchamber and the chamber of the acc.pump are only devided by the marble which is the suction valve. If you not operate the acc.pump (so you have the gaspedal at a fixed position) they would be communicating. It is only when you use the acc.pump that the suctionvalve will be forced close and the top marble will open as a pressurevalve.

You can check the official manual in the dutch carburator topic.

viewtopic.php?f=60&t=23486

[Jeroen]

A manual in Deutsch even! Direct link: https://files.bmwclassic.nl/E21/Carbs/Ha ... rgaser.pdf

[E21-driver]

Hi Jeroen,

thanks for that, very nice document. This weekend, I will check also the ignition. Maybe I did a simple error.
Murat

[E21-driver]

So,

I have made some trials today. And I checked first the dizzy. It was turned 180 degrees. Obviously I have mixed both tdc's.
I have re-installed it correctly. This made a big improved in the first starting trial. The inginiton fires now in right order.

But same situation again. There is no idle and it dies again. Then again the next trials are very hard. The exhaust blows enough black dust to set the garage under fog. I have also checked water and oil, no mixture. Mechanically the engine is proper. And I set the nozzles two turns out, as Peter said.

It seems so me, that carb is overfloating immediately. The new fuel pump was one from aftersales. Next week I will get an original Pierburg pump, then I will try it again. There must be something with the carb or fuel supply but I can't find it.
I didn't install the fuel non-return valve.

Somebody other ideas ? Please comment. Thanks.
M.

[mr edd]

http://www.e12.de/archive/06/000000020/04axxl99.htm

might be some help..

[E21-driver]

Hi Mr. Edd, thanks, very nice help.

Today, I have opened my spare DIDTA from a 316 just to check, and I have found two differences to the installed one: first the pipe Peter told me is closed by a screw. When you open it, you get first a tiny small spring, then you can see below the marble.
Please have look on the picture:

Second suspicious point is the arm of the acc pump. When you open or close the cover with the 4 screws, should there be a tension on the arm ? The spare Solex hasn't, but the Solex of my engine has a tension on the arm / the spring when opening or closing the acc cover. => they have different adjustments.

I have the feeling, that there can be caused a permanent overflow by these two points, what do you think ?
M.

[Peter V.]

The constant overflow as you mention can not be caused by the acc. pump. That is a mechanical pump with a membrane which has to be moved to get the pump working, it is not that if it is halfway constantly that it gives petrol constantly.

[E21-driver]

I see. Now I got it. But do you think a missing spring of the little spring valve can cause the problem ? When cleaning the carb, I can't remember it to be there. The marble can't stay down in idle, and would be easily lifted up.
M.

[Peter V.]

It will not give an overflow problem. It only gives you a not working acc. pump.

If you remove the airfilter and you have petrol in the floatingchamber you can check if the acc.pump is working.
Just move the throtle and look inside the carb, when you see a small petrol injection the acc. pump is working and you are sure that the suction and pressurevalve are there and working.