Zenith idle problem

[lsquaredb]

Hi everyone,

My front carb is running too rich and the sparkplugs are fouling in about 20 miles. Turning the idle mixture screw doesn't do anything at all. The carb was rebuilt recently. Do you have any suggestions? Thanks.

Leonard

'70 2800CSA

 

[Stevehose]

Sounds like a blockage, remove the mixture screw and do some carb cleaner/compressed air treatment down the hole and inspect that it is clear. Check that your float is not hanging up in the open position. It can catch on the gasket if not trimmed correctly during a rebuild. Check that the needle valve is clear of dirt and functioning correctly. Check that the choke flaps are opening all the way when warm.

 

[GolfBavaria]

And the needle valves that come in the rebuild kits can be crap (depending on what kit you bought). See if the old ones are still good, hopefully you saved them, install those and see what happens.

 

[mulberryworks]

I rebuilt mine and didn't know about the gasket possibly hanging up the float. My front carb overflows the bowl and makes the car run so rich it will stumble occasionally. I had heard about the poor quality of the needle valves and kept the original ones. I haven't taken the carbs apart yet to fix the issue.

Ian

 

[Philippe db]

I spend a lot of money on endless tuning and cleaning my Zenith's. If you don't have a full history on the life of your carbs IMO there is only one way to go. A complete professional rebuild. Cost a little money and takes some time but what a world of difference. Perfect start, perfect idle, whatever the engine temperature and smooth power delivery. The best invested in my E9 so far.

 

[lsquaredb]

Thanks for the suggestions. The carb was professionally rebuilt, but sometimes pros goof. Hopefully the problem will be fixed today.

 

[GolfBavaria]

I spend a lot of money on endless tuning and cleaning my Zenith's. If you don't have a full history on the life of your carbs IMO there is only one way to go. A complete professional rebuild. Cost a little money and takes some time but what a world of difference. Perfect start, perfect idle, whatever the engine temperature and smooth power delivery. The best invested in my E9 so far.

I agree but even a professional can miss using new needle valves vs. old ones for instance (thinking he/she is doing the right thing by replacing them). And I agree they do run great after a rebuild but just as important is to get a great tune. That can be an art. They can be rebuilt perfect, but if not tuned properly, you will and can have issues. The tune made a world of difference with mine. And even after you get it tuned just right. They need to be used and driven around for a bit after the rebuild (in my case a few hundred miles). Then re-tuned. Silky smooth now.

 

[bavbob]

I vote float bowl hang up. There is also the "cold start valve equivalent" which is the flat square that has a single female lead. I imagine if that is stuck open, car can run rich also.

 

[deQuincey]

see this guy solving the "gasket hanging up floater" issue,

BTW, he is not a "pro", he does not even wear gloves :-0

 

[deQuincey]

tunning is also important, yes, but do not forget points and ignition timing

then you can synchro the carbs, otherwise you do not know where you are

a word about carb pros,
i ended up doing mines as a result of visiting the most famous carb pro guy in the area, a total disaster, the essential issue to me was he was not humble enough to read the manuals, he ended up using the central screw to tune the carbs, something that is only to tune them at 1700 rpms, but must undo that screw at the end of the procedure

 

[lsquaredb]

The shop found something wrong in the carb and fixed it, so it's running a lot better than it was. I'm not sure what they did.

Anyway on to the next idle related problem. When warmed up, the engine idles very smoothly at 950-1000 rpm in park and neutral, but only about 450 in drive. The car has the ZF automatic. Is there some transmission related adjustment that's been overlooked? Thanks.

 

[deQuincey]

The shop found something wrong in the carb and fixed it, so it's running a lot better than it was. I'm not sure what they did.

a small rat ? a piece of fruit ?
you should ask them, it might be relevant

 

[Ohmess]

In my car, which had been an automatic, there was a linkage between the bell crank and the transmission, which I believe was designed to cause the transmission to downshift if you quickly pushed the accelerator to the floor. This linkage could be having an effect on your idle speed if it is not set properly.

 

[lsquaredb]

I was able to drive the car about 100 miles yesterday. I ended up stopping at a BBQ joint in New Hampshire with a sign that read 'Horrifying vegetarians since 2003'. The car was miserable in town because of the low idle, but ok on the open road and freeway, but not as powerful as it should be.

The guy who worked on the carbs has gone home before I picked up the car, so I don't know what he did.

I'm trying to adjust the accelerator cable according to this section in the service manual:
http://e9-driven.com/Public/Library/BMW-E9-Manual/pages/en/24000040.html#refertoc

The tension element is set to the correct length. The instructions say to press the throttle valves to full throttle position with the operating lever. Is full throttle with the butterflies vertical? If vertical is 12:00, then the butterflies only open to 10:00. The secondaries don't budge from fully closed. Should they be opening when I move the lever? Engine is off and cold when I'm doing this.