Initial rough choke running

[markee]

Hi all

I have a problem with cold starting on choke which I wondered if someone may be able to help with?
My car is a 1977 124 Spider 1800, the carb is a Weber 34 ADF which was new 6 years ago and has less than 10k on it.
The problem is that on initial cold starting it takes several attempts to start then when it does start it runs rough including sometimes spitting through the primary barrel, after a couple of minutes the idle speed picks up and it starts to run smoothly on fast idle.... now the thing I can't understand is that the choke is set by me pushing the gas pedal to the floor before turning over, so the flap is closed and the fast idle cam is engaged with the adjusting screw, having monitored it it never fails. (I have noticed slight improvement with the flap slightly open). The car runs beautifully when warm, idles smoothly, and there are no vacuum leaks or fuel feed problems, the battery is healthy and the plugs, leads and ignition system is mostly new though I had this problem before changing anything. I took the carb apart last week and cleaned the jets and examined the choke unit but it has not made any difference. The only thing I have not changed are the carb diaphragms. If anyone can help with this I might still have a full head of hair before Easter!

Thanks
Mark

[vandor]

I would start it and let it run rough for a bit then kill it and check the plugs. Is it rich or lean? That will give you a place to start. The fact that it spits through the carb would tell me it's lean, but need confirmation.

Have you started it with the aircleaner lid off and observed how the choke plate behaves?

Also, are the duel points still functional? It may be running rough on the 'cold' set of points and then when it switches to the warm running set it runs ok.

[markee]

It has Pertronix electronic ignition fitted to the original Marelli distributor.
The plugs are a healthy colour and of course I have observed the choke plate hence knowing it is closing!

[vandor]

So when does the choke butterfly move when it finally runs fine, or it is in the same semi-closed position, and it start running fine?

[markee]

It starts to run ok before the flap moves from closed.

[So Cal Mark]

there is a choke pull-off that can be adjusted

[markee]

I tried adjusting it but no luck, can you explain it's function and what the pull off diaphragm does?
Thanks
Mark

[So Cal Mark]

it opens the choke once the engine starts to prevent over-choking

[markee]

Thanks for that, can you think of any ignition problems that would only show up when cold starting?
Mark

[So Cal Mark]

ignition problems can be worse during warm up since combustion is not ideal yet. The points-type systems are just not adequate

[majicwrench]

With all due respect, points work fine, have worked fine for generations. Electronic is better, but so is FI, modern computerized cam timing, all sorts of new things are better. A 2013 Mustang is better. But points are fine.
With enginge cold choke plate should close all the way once you open and close throtle. Once engine fires, the choke pulloff should open the choke plate a small amount. If it opens it too far, the engine will go lean and stall. If it does not open it enough, engine will run too rich, sometimes black smoke, blubber, and stall. The adjustment is pretty critical to making a carb work well. Adjustment spec is in manual somewhere, or with a carb repair kit. The diaphram is generally rubber and can fail.
Keith

[So Cal Mark]

points may work fine, but that system doesn't produce enough spark for combustion in less-than-ideal conditions or for performance use. Horses and buggys are great too, but there have been lots of improvements in the last 4 decades

[manoa matt]

There are a few adjustments that can be made to the choke. The only one described in the manuals refers to indexing the automatic choke housing to the carb. The other adjustments were detailed in a workbook that was a supplement to the factory manual. The workbook is for the 32ADFA, the 34ADF's little brother, however I have a stock 78 with a 34ADF and have set it up with specifications for the 32ADFA and it works fine. Send me an email and I can send you a PDF copy of the workbook.

matt.scarton@gmail.com

[markee]

Update...I have replaced the choke pull down diaphragm and the difference is amazing! The car starts first time from cold and idles evenly. Thanks Matt for your information and I will e-mail you for the worksheet.

Mark