Carb - choke setup on Auto Sprint

[gmsclassics]

I've never really got this right since I put this car together from my 'parts bin' some five or so years ago. This is a midly tuned engine with carbs (non waxtat) that were never used on this engine before, and linkages that were just from a box of old parts from various engines so there may be a mismatch. Linked to an 1850 auto box that has probably seen better days but does function as I would expect. Carb setup when warm is fine and fuel economy is as I would expect (28mpg) compared to my manual Sprint (33mpg).

Engine starts on the choke easily but when still cold, finding a level of revs low enough to keep the engine running when put in drive without stalling is problematic. Fine at 2000-2500 rpm but then needs a firm foot on the brake to avoid a loud clunk and making a flying start! Does seem difficult to maintain a lower rev level on choke (say 1500rpm) even when in neutral.

I never driven another auto Sprint so not sure what is normal.

Appreciate advice on both carb / choke setup for this arrangement as well as what I should be expecting in terms of rev levels when cold on choke that should be maintained when in drive.

Time I got this sorted once and for all.

Geoff

[soe8m]

Try as lean as possible on the choke.

What also can cause this is a worn dizzy. But more noticeable on automatics. When there's slack in the advance system lowering the revs a bit by putting in D for example can cause the dizzy to retard, revs drop, retard more and stalls.

Jeroen.

[AlanH]

My Sprint revs at about 1200 on full choke and drops to about 900 when put into into drive (with a massive clunk !!).

When hot it idles at around 800 and drops to around 600 when in drive. So there is obviously something very wrong with your setup.

Are your carbs balanced? You say that you got them out of a 'parts bin' so why not give them a thorough check over.

I have just spent a very (joyful?) Saturday setting the carbs up on my 1850 going round and round the idle-mxture-balance cycle, it really is a bit of an art.

Having said that I find the Sprint a better drive with the auto than the 1850.

Just one other thing, the Sprint auto box has an oil cooler the 1850 does not. I'm not sure how significant that is perhaps Harvey can tell us.

[soe8m]

You need the cooler on the sprint.

Jeroen.

[dollyman]

hi, have you tried adjusting the choke idle screw?
my auto was at 2000 rpm on choke when i bought it, but after simple adjustment i have got it to start on choke at 1000 rpm which drops to 900rpm in drive when cold
you could also do damage to the box at those revs
cheers, tony.

[AlanH]

Goeff

Just seen from another thread that you have a cooler fitted so it should be OK.

[Jon Tilson]

You should achieve a reasonable fast idle if you set the fast idle adjuster screws up right. You want about 1100 rpm on an auto.

These are the ones underneath the linkage at an angle. Its obvious how they work on the cam that rotates when you pull the choke out.

Autos will idle smoothly a bit slower than a manual car as the torque converter has more inertia than a flywheel. You can get down to 800 rpm
easily enough and that will smooth drive takeup and lengthen box life.

Jonners