Stromberg 175cd Carb Tuning

[Direwolf]

I wonder if anyone can help me with some advice (other than ...take it to someone who knows what they are doing!)

My series 3 2+2 1971 (ex USA with emissions removed) was running rich and l needed oil change etc and took it to a classic car garage not too far from me in France but after l got it back it was not running too well as after running for 20 to 25mins it would start misfiring and hesitating on acceleration.

With pressures of work then lock down l couldn’t take it back. I thought ..‘how difficult could it be!’. Yes, you know where this is going...after reading as much as l could from the Repair and Operation Manual and all other articles on the KB....cut to the chase...l seem to have taken a working(but not very well) car, and turned it into a right Horlick’s!

I checked diaphrams and the needles and set them flush with the carb pistons lower surface to try to get the mixture to a correct setting. Trying to get her running l reset the idle screws and linkages as per the manual.
She starts with choke although running rough,but easing off the choke as it warms up it has a lot of vibration, following the manual for easing off the idle screws to reduce the revs (to 650-750rpm) she cuts out below 1000rpm and is difficult to start. I noticed a small amount of blue smoke coming from the front right carb ?(the small hole just under and forward of the air intake hole).
Before easing it down in revs l checked the vacume and the carbs seem similar front to rear but the right to left seem a bit different (thus vibration l guess). I have checked the throtle’s open at the same time and there are no known vacume leaks,the spark ,timing and fuel seem to be Ok.

l cannot get it running for long and l have a steep incline to get out of my garage under the house and it has no torque to get up the drive to take it to an expert/garage. Can anyone give me a hint at what may be my mistake-other than having a go!!? Many thanks.

[Bfastr]

sounds like its too lean now. you might check carb synchronization too.
if it requires choke all the time and it lacks acceleration at higher revs, and given why you took it in , I would try making it rich again. just a guess. plus its a simple thing to try. if you have the adjustable needles make notes of how many turns and you can always go back.

not sure where the jets belong on a V12, but the same carb on a S2 they are 0.100 below the carb body.

[lowact]

I reckon u have a vacuum leak. Note this would be same as too lean prognosis. Go over y intake manifold, plug/seal off every single offtake, incl. Brakes, distributor, crankcase. You'll idle up the incline from yr garage.

[Direwolf]

Thanks very much for your reply’s, l have had another look around for vacume leaks-thanks l wasn’t aware of the connection to the brake servo-all seems good, so l tried enriching and it seems better although still a fair amount of vibration at low revs probably just a case of tweaking the mix more.
Thanks again for your time. Bob M.

[PeterCrespin]

I would stop the cheque to the tune-up shop or ask for your money back.

This perhaps has nothing to do with carbs but your symptoms sound like some mixed up HT leads. Maybe they messed with plugs or distributor and replaced some leads wrongly?

When removing the US emissions stuff people sometimes fit a later vented distributor cap, which sucks air through to prevent distributor fires. Maybe they connected the vacuum to a manifold instead of air filter source, giving an air leak that way? Just a guess, but definitely check the HT leads carefully.

[Adamski]

If you have the thermostatic temperature sensors in the side of the carbe someone may have backed them off and this allows air in. Lethal.

[Direwolf]

Thanks Peter and Adamski, Sorry for delay in response Peter but l take in to account your ideas.

l have been delayed by work from spending as much time on her as l would like but she is still not starting after checking the dizzy and new plugs, coil,ballast and rebuilt one carb which was flooding slightly which could have been a cause or a consequence of me pressing the go pedal with choke out in desperation to get her running!!
I changed the HT leads yesterday maybe the old floppy wires were looser than l thought, tomorrow l will try again.

Can any wise people out there give me a clue how to check the choke setting is correct? I know the manual suggests ..”Start engine (already warmed up) then slacken the locknut and adjust screw until idling speed 1600 to 1700.” If you can’t get her started (maybe because of the choke setting) how would l set it without warming the engine?

Thank you for any advice.