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Stromberg CDSE fast idle setting

Posted: Thu Mar 16, 2017 1:19 pm
by Vox
Hi all,
In the on going search to find why my car is a slightly reluctant cold starter I am re-visiting the setting of the fast idle cam.

The car is a 1972 pre face lift 2000 on Stromberg CDSE carbs (the ones with the starter box and the temperature compensator) - ignition side is all good (and new old stock) and compressions are all around 150psi (except number 6 which is around 180!). Car will usually fire instantly you first touch the key but not catch, it will then take usually two or three more fairly long churns before starting (sometimes more) and then run badly for 30 seconds or so but after a bit of a rev it will be fine, can be stopped and instantly restarted and will then be good all day, even if a little choke is needed later.

It feels to me like the balance between the choke and the fast idle is not right. I have tried setting it as per the Leyland manual with a 5/16" bar between the inside of the cam and the choke stop and make the adjusting screw just touch the cam but the profile of the cam is so shallow for most of its travel it is not really opening the throtle any and barely moves beyond normal tickover speed. The manual goes on to say 'remove the bar, push in the choke and pull it out again and check fast idle is in the range 1100 - 1300rpm - does this mean check with the choke fully out or at 1/4 or so choke (where I would have thought fast idle should be)? If I set it around 1/4 choke it is WAY too fast with full choke but set like the manual it is no faster than normal tickover at 1/4 choke.

It is probably not helped by the fact that becasue I have fitted after market heat shields getting at the fast idle screw can be difficult (bracketry in the way from above and shields in the way from below) and all the time I am fiddling the engine is rapidly warming up so changing everything anyway!

Anybody know the secret to setting this up - I'd love to know!


Re: Stromberg CDSE fast idle setting

Posted: Thu Mar 16, 2017 4:24 pm
by Charles H
Just a thought, have you checked how much fuel is in the carbs before the first start? It almost sounds like the fuel pump is pumping fuel back to the carbs before starting correctly. It could be that the fuel is leaking past the 'bung' at the base of the dash pots, the one that the earlier carbs had the jet assembly through!!? IA dried out 'O ring@ perhaps?

Re: Stromberg CDSE fast idle setting

Posted: Thu Mar 16, 2017 5:04 pm
by Vox
Hi Charles,
No fuel leaks, carbs were striped and all new gaskets/float valve etc. Float heights correct.
I originaly wondered about whether it was waiting for the pump but I have also tried filling the flaot bowls via the priming lever on the fuel pump before starting and it seems to make no difference.

Re: Stromberg CDSE fast idle setting

Posted: Thu Mar 16, 2017 9:37 pm
by johnnydog
Continuing Charles' theme, are they over fuelling? From experience, fitting new float valves during carb overhauls has caused me no end of problems. Although genuine Zenith, they don't seem to be manufactured to the same quality, and correctly gapped relative to the tab of the float, I have had flooding, and starting problems with over full float chambers, which were all cured when I refitted the original old float valves.
I have previously had cars with your carb set up fitted, and I personally don't like them. I have in the past removed them and fitted a pair of standard Strombergs CD's, which are a lot simpler to set up.

Re: Stromberg CDSE fast idle setting

Posted: Sun Mar 19, 2017 11:04 pm
by Dazzer
Sounds as though its running a little lean rather than anything to do with the choke. As an experiment half to three quarter turns on each carb and try it for a while. Easy to return to previous tune if it makes no difference. Cheers Dazzer

Re: Stromberg CDSE fast idle setting

Posted: Mon Mar 20, 2017 1:12 pm
by Vox
Johnnydog - when I first had the car I used to suffer from flooding and took a few new float needles until it was fully cured (ones from Chris Witor with Viton tips and filter mesh) and I can't see any signs of flooding now. I was thinking over fueling but more from the point of view of there being too much choke in relation to the fast idle setting. The float chambers can be half empty and it doesn't make a difference.

Dazzer - it could be too lean, although I like Strombergs generally (far preffer them to SUs) I don't get on with the adjust from the top set up on the CDSE and mixture is always something I am fiddling with, partly because I tend to get issues with being too rich when really hot (hence adding the heat shields although they didn't seem to help) currently 2 and quarter turns from maximum richness, set by lifting the piston method but I have had them set much richer than this and still had the same cold starting issues but worth another go and as you say easily put back.

I was just hoping that somebody had a fool proof method of setting the fast idle so I could set it and rule it out - on my old 13/60 Herald (which admitedly had a starter bar rather than the starter box) you set the gap between the cam and the fast idle screw at 1/16" and it would start on the button every time.

It may be just that I am asking too much of a 45 year old 100k plus big 6 to start instantly from cold - a lot of people say they have to churn theirs over a bit before it starts!

Thanks for all the input!


Re: Stromberg CDSE fast idle setting

Posted: Tue Mar 21, 2017 2:43 pm
by atom
I have exactly the same problem with my CDS carbs.
Still didn't find a solution.

Re: Stromberg CDSE fast idle setting

Posted: Wed Mar 22, 2017 11:02 am
by Clifford Pope
I think all chokes of this kind work on the following parameters:
When the choke is pushed in it really must be fully Off at the carburetor end, not slightly engaged dependent on the springiness of the cable.
In the choke-in position the throttles must close so that their stops are just clear of the choke cams.
When the choke is pulled out it should should after perhaps 1/8 inch of movement start to engage the cams on the throttle stops so that the throttle opens to give a tiny amount of air, progressively more with more choke. ie not too choked.

I don't know what that equates to in terms of gap at the cam, but whatever it is is just a way of saying "open the throttle a bit as you pull the choke, but not before".

Every single carburetor car I have owned (Roadster, Mayflower, LandRovers, Stag, Volvo 240s, Renault 4, Austin A30) started from cold first turn by giving full choke and no accelerator. Then the instant it fired and was running I put the choke in to about 1/2, blip the accelerator so that the engine catches and idles nicely, then ease the choke in more, as much as it will take but still idling smoothly.
On pulling away, especially if up a gradient, it may need a second's quick pull on the choke just to give a burst of richness, and then off. No more choke needed, unless on a very cold icy morning it may need a fraction of choke briefly if I have to stop at a junction within the first half mile.

I have had trouble with needle valves ever since they started improving them. The old all-brass type were fine, but the rubber-tipped ones tend to stick shut sometimes, and there is no proper way of adjusting the fuel level. I've just replaced one that wasn't cutting off properly, letting the float ride too high. Looking through a box of spares I found they weren't even all of the same length. Obviously the valve has to be fully shut off before the float touches the chamber lid.

Re: Stromberg CDSE fast idle setting

Posted: Sat Mar 25, 2017 7:24 am
by Dazzer
There is a measurment for the choke cams, which for the life of me I cant remember. However Ive never used it. As long as there is a small clearance and the choke is off when disengaged it will work fine. In a reasonable state of tune it will only be used momentarily on starting from cold. Once started straight in and off you go, might be slightly hesitant for the first minute or so but thats how all my Triumphs have worked. In warm weather it doesnt get used.
There is a valid point with using older original parts. I run 175 strombergs off a TR4 on my 2000 rally car and I settled for the early bakelite type floats, they do have a different float height setting though not referred to in any manual post 1965!
Ive had a couple of incidents with the original metal connecting U pipe between the 150 carbs internally corroding at the bottom of the U and affecting the needle valves with minute particles of rust.

Re: Stromberg CDSE fast idle setting

Posted: Sat Mar 25, 2017 1:48 pm
by pete lewis
one thing you need to check on cdse is the temperature compensators
these small bimetal operated valves can when old be open when they must be shut,
take them off the, small plunger should at normal operating be seated in the end of the cast body, if the plunger is off its seat , do the small nut up to close the thing completely, its more important they are shut when setting idle mixtures as it bypasses air past the throttles to raise idle and weaken when getting too hot under the bonnet
buckeye triumphs do a good write up of testing but really they are best corked up or removed and blocked off for ever

if they are open you will never set the idle mixture

the base setting for biased needles is set the small delrin washer at the head of the needle level with the base of the air piston