Applying choke

[sujitroy]

When pulling out the choke is it necessary to increase the idle? I have an auto, and want to limit the idle speed while the car is on choke.
Sujit

[gbb483]

Assuming the auto is the same as the manual, then there is a linkage between the choke (starter box) and the throttle on the carburettors. Opening the choke applies a small amount of throttle.

[DJT]

R.O.M. 19.15.02 for choke adjust. But be aware that the ROM suggests that there is a fast idle cam on both carbs, but there is only one, fitted to the LH carb.

[SteveD]

With my auto BW35, I pull the choke out fully, start the car it runs at about 1500rpm and I leave it for about a minute then I push the choke fully home and it idles roughly at about 500rmp so I pull the choke out a little bit to get it to tick over at about 1000 rpm and then set off and push the choke home after about 5 minutes and it idles at about 600rpm. Is this OK?

[sujitroy]

This brings up another question. On both my manual and auto stags I only have to pull out the choke about 1/4". does this imply say the cars are running rich without choke

[trunt]

This brings up another question. On both my manual and auto stags I only have to pull out the choke about 1/4". does this imply say the cars are running rich without choke

Maybe, but weather and temperature are also factors - California boy! I use full choke in Winter and immediately go to 1/2 then as soon as I get a mile or two it gets pushed in to just give a little extra idle.
In Summer maybe 1/2 to start and it gets pushed in a lot quicker...

I have seen some who change the profile of the choke cam by filing it, but I would try adjusting first, sounds like yours is a bit too much idle so just back it off and see.

[Stag About Town]

If the choke is set correctly to the cam as in the setup instructions you should pull out the choke control to start from cold and then push it in to about half and inch from fully in. At that setting the engine should be running above idle revs but the mixture will not be enriched. This is more important for autos as you can't dip the clutch to keep it going like at a T junction soon after starting. Push right in when warmed up. From memory the round bar used to set the stop to the cam is about 5/16th or 8mm.

[gbb483]

0.067"

http://www.grampianstags.net/Stromberg%20CD175%20Carbs.pdf

[DJT]

From memory the round bar used to set the stop to the cam is about 5/16th or 8mm.

Correct 5/16". Although the early ROM states "on both carburettors in turn", but the fast idle cam is only fitted to the LH carb.

IMG_0392.jpg

[gbb483]

Is the cam different for manuals vs autos? I only ask as I've been rebuilding my carbs and I have reason to suspect they didn't start of life as a pair. And the accelerator linkage has the hole to attach the kick down cable (which my manual doesn't need). So it is possible the cam came from an automatic (or maybe some other car which uses the CD175s). I believe the auto has a higher rpm than the manual.

[DJT]

Having rebuilt the carbs on my previous Mk1 manual Stag and those on my current Mk2 auto Stag, I have not noticed any difference in the choke cams. They all had the same hole to mount the kick down cable.

Rpm is similar for both.

[gbb483]

Thanks

[sujitroy]

Correct 5/16". Although the early ROM states "on both carburettors in turn", but the fast idle cam is only fitted to the LH carb.

IMG_0392.jpg

I've been doing a bit of thinking and think my car is running a bit rich. It runs well, but I can start my car with the choke pulled just enough to be at fast idle. At this fast idle point, I don't think any of the holes in the choke unit are exposed to allow additional fuel into the carbs to assist in starting. Please correct me if I am wrong. An experiment I can try is once the car is at running temperature, I can pull out the choke to the fast idle point and see if the car sputters.
With the current set up the car when warm drive well. What are the running symptoms of a car which is running rich?

Sujit

[mole42]

With the current set up the car when warm drive well. What are the running symptoms of a car which is running rich?

Sujit

High fuel consumption - when my ZF car was running properly I’d get 32 miles to the UK gallon. It’s also, if running very rich, possible to smell the excess in the exhaust.

[richardthestag]

black sooty exhaust, noticeable smell of fuel in the exhaust.

Pretty easy to tune a set of carbs up using basic tools, the manual explains how to do this but there is also some chap on youtube who gives away the "secrets" for free.

CO tester if you have one should really be reading below 4.5%co, it is possible t get stroms running at 2.5%co but in my experience they run a shed load better at 4% ish

choke pull is not an on/off switch, it will need adjusting based on local environmental factors