Idle Adjustment

[LusciousLancia]

I have a stock carb on the ol' '76 Scorp. It runs seemingly well, but it races at about 1500 rpm at idle. What I thought was an idle adjustment screw on the carb (a screw with a spring on it) doesn't seem to have any effect on the idle speed at all. What is this screw? And how do I adjust the idle? I was thinking that I could adjust the arm that attaches to the accelerator cable, but I thought I'd better ask before I go tearing into anything.

Also, this is an unrelated question, but there's two rubber hoses that attach to the side of the carb (right hand side if you're standing at the rear of the car). They seem to be running antifreeze through them. Why?

Thanks for all your help, as always!

Dan

[Will]

1)Idle MIXTURE screw (from your description I think)

2) Start by finding the vac leak. An idle that won't drop below 1500 and the idle circuit adjusted very rich are usually indicative of a vac leak where somebody tried to adjust the carb to compensate, at least in my experience. The Scorpion has an inlet manifold and plumbing that's prone to small vac leaks, particularly the myriad of small hose connections (five, I think) under the front edge of the manifold. Depending on how meticulous the P.O was, one can usually find old split vac caps or bits of hose with an assortment of old bolts and/or golf tees shoved into them to make a seal (I kid you not, I've found all of the above on Lancias- well, maybe the golf tee was OEM ;) )

3) Water activated choke (again, from your description). Coolant heats up and, well, the name is self-explanatory.

Ciao.

[LusciousLancia]

I'm guessing that if you loosen the three screws around the choke that it will adjust by spinning clockwise or counterclockwise? At least this is how other chokes I've worked on have worked. If this is true, then is there any specific place where it should be? I don't see any marks on it like I've seen on other carbs. It looks like a pain to get that screw under the choke loose, so I thought I'd just ask first!

Dan

[Will]

Yeah, well....not exactly.

The Webers like your DGAV ( the A is for "Acqua" or WATER activated choke) have a lever/pivot under that cover which has a fast idle adjust screw- it's another one of those little screws with the anti-vibration spring around it. This lever is connected to the rod that goes to the throttle shaft.

But if you open the choke by hand (assuming you've already done the step-once-on-the-gas thing) and then rotate the throttle shaft towards the closed postion, the fast idle lever should be disengaged (read: no more fast idle). That lever rides on a little cam-like thing that is connected to the choke shaft pushrod. At least, that's what I remember, subject to my memory lapses.

Sounds like you could use a diagram- suggest you get yourself a copy of the Haynes Weber Book.There are others but the Haynes one is the easiest IMO to understand. I can fax you over a diagram or two if you PM me with your fax number.

Personally, I would persue the vacuum leak thing first. There can be other bizarre things like the throttle linkage flipped around inside-out, or that fast idle cam in the water choke might be your culprit, but IMO you need to systematically problem solve, and you need to be damn pragmatic about it, or you end up going in circles. Well, at least I do.

[ecohen2]

Will is exactly right and I spent months trying to figure out almost the identical problem you are having.

In my case, someone had gutted the little solenoid that is sitting on the carb and had put a rubber hose with a bolt on a vacuum line near it to seal off one part of the emission system. Unfortnately the rubber hose was brittle and had torn near the bolt so I had a vacuum leak in a big way but didn't know it. After checking all of the hoses and replacing one of them my engine magically started to idle properly.

Although I am no expert, the smallest leak seems to cause huge problems.

Ed

[LusciousLancia]

What did you (and anyone else) do to block off the half a dozen nipples on the carb that you don't need if you eliminated the emission system? I guess this very well may be my problem, since I just blocked off the hoses temporarily to get the thing started. I am in need of a more permanent solution.

Dan

[Will]

If you drop the mani and pull the nipples you'll be left with three holes, viewed from the top let's call these LEFT, FRONT, and RIGHT, where RIGHT is the old EGR bung.

The FRONT can be plugged with 1/4" NPT plug with a few wraps of the thick (gas line) teflon tape on it.

The LEFT can be tapped (without reaming) 1/8" NPT and then you can use a 1/8" NPT plug with a couple wraps of regular teflon or some dope on it.

The RIGHT (EGR bung) can be sealed up by using an old head temp sender or switch (which has the bonus advantage of confuising the $#%^^% out of the next owner!! :) ) or it can be tapped (again without reaming) to 3/8" NPT and sealed with a plug and some tape/dope.

Careful with the tape because you don't want shreds of it in the inlet tract. Fortunately, these are not items that have to go in and out so you can get away with tape, whereas most fittings on the car call for paste.


Alternately, if you really want to, you can order all the correct metric plugs. Iv'e been ridiculed for using Home Depot etc. plumbing parts to fix half the stuff on my car, and one person went so far as to say using a brass plug would promote a galvanic reaction (in air no less) that would rot the manifold away.

I fit pipe as a fairly significant percentage of my life, and Scorpion inlet manifolds are practically free for the asking so I have no problem using parts that are readily available from my local hardware in situations where they work. If you really want to buy anodized aluminum metric plugs, go right ahead since that works too- more trouble than it's worth IMO, but to each their own.

Any kind of plugs beat a bunch of 2" hoses with stuff stuck in them, or vacuum caps that blow off on the first backfire.

[DJ]

The Webers like your DGAV...

Will,

If Dan indeed has the stock carb on the car as he stated, it's a 32 DATRA, not a DGAV. Maybe I missed something in this thread? Regardless, you can find a PDF file containing every Weber exploded diagram and parts list that I've ever found in the downloads section under "Miscellaneous Files".

Link is here (Weber Carburettor Data). (http://lancisti.net/index.php?ind=downloads&op=entry_view&iden=7)

[Will]

Oh, of course DJ is right- I had a brain break moment. I just can't keep the darn things straight anymore- I'll continue to blame Wednesday night's torpor-inducing tequila party for as long as I can, maybe I can wring a couple of days out of it. I'd try the excuse of aging, but DJ's my senior by quite a bit- maybe I should just blame it on stupidity :)

[LusciousLancia]

Yes, it's the stock carb. Of course, if carbs didn't cost many hundreds of dollars, it wouldn't be! ;)

Thanks for the link, DJ.

Dan

[LusciousLancia]

Upon downloading the file, the 32 DATRA doesn't seem to be listed. Is there a very similar one?

Dan

[DJ]

Sorry, Dan.

I should've mentioned that. You should find that the 34 DMTR is very close in most respects except for the choke mechanism, which is manual.

[capnjoe]

My '76 races at idle too, but it's not the carb. it's the throttle return spring. If you grab the throttle lever by hand and pull a bit, you will know right away if your fast idle goes away. Then you can figure out how to replace that spring, and tell me!

Yours aye,

Joe

[SubGothius]

I'm guessing that if you loosen the three screws around the choke that it will adjust by spinning clockwise or counterclockwise? At least this is how other chokes I've worked on have worked. If this is true, then is there any specific place where it should be? I don't see any marks on it like I've seen on other carbs. It looks like a pain to get that screw under the choke loose, so I thought I'd just ask first!
While it's true that you can adjust the auto-choke temperature calibration that way, that's not the way to adjust the choke (butterfly+fast-idle cam) mechanism itself.

To elaborate: coolant flows thru a capsule on the carb via those two hoses you mentioned; as the coolant heats up, a bimetal spring uncoils on the backside of that capsule (outside of the chamber where the coolant passes). The hooked outer end of that spring fits into a forked tang on the choke mechanism, gradually opening the choke butterfly plate, and backing-off the choke fast-idle cam that keeps the main throttle lever from completely closing to its normal (hot) idle setting.

The collar held by 3 screws you described sounds like the part that holds that coolant capsule w/ bimetal spring onto the auto-choke mechanism housing. There should be a barely-discernable score mark on top of the coolant capsule, which lines up with a similar mark on top of the auto-choke mechanism housing, to calibrate the coolant temperature to auto-choke operation. There should be no reason to de-align those score marks for normal operation; just be sure they line up whenever you put things back together.

You may find it worthwhile to remove that coolant capsule, just to manually operate the auto-choke mechanism by hand and verify that everything works, properly lubed up, no springs broken, etc. Of those 3 screws holding that collar down, once you loosen the easiest one or two of them, you can then rotate the capsule to allow access to the remaining screw(s) until the collar comes completely undone, then just pull the capsule straight off. When refitting the capsule, just be sure that the hooked end of that bimetal spring fits into the forked tang on the choke mechanism, and align the score marks on the capsule and auto-choke housing before completely tightening all 3 retaining screws on the collar.

The basic rules of thumb for carb idle/mixture adjustment go like this:
Thoroughly warm up the engine, so the auto-choke is fully opened and fast-idle cam is fully disengaged;
Tighten the Idle Mixture screw 'til it's lightly seated all the way down (but don't force it -- threads strip easily in that aluminum carb body!) -- this is the screw in the carb body/base with the anti-vibration spring on it;
Back out the Idle Mixture screw by ~2 full turns;
Back out the Idle Speed screw until it is just barely touching its stop on the carb body -- this is the other screw with anti-vibe spring on it, but attached to a main throttle lever outside the carb -- a strip of thin paper inserted between the screw tip and its stop on the carb body is handy for determining when the screw is barely-touching its stop;
Screw in the Idle Speed screw (against its stop) by ~1-1.5 turns;
With the (warmed-up) engine running, adjust the Idle Speed screw until idle is at ~800-850 RPM;
Screw in the Idle Mixture screw until the engine starts running poorly or dies, then back it out again by ~1/4-1/2 turn increments until it settles into an even idle again;
Readjust the Idle Speed screw to hold idle at ~800-850 RPM.
(Distilled from more detailed instructions here (http://redlineweber.com/html/Tech/carburetor_set_up_and_lean_best_.htm), cf'd with the Haynes manual for Betas.)

[LusciousLancia]

Wow, excellent advice. Thanks very much!

Dan