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Discussion Starter · #1 ·
My 1974 Spider finally has a completed air intake and exhaust so I can really start to tune the engine. No matter what I do I cannot get the engine to idle cleanly. I have tried adjusting the idle screw on each carburettor (Weber 40 DCOE 31) to no avail. The best I got was an "idle" at 2500rpm with the idle mixture adjust screws 2.5 turns out from fully tightened. In reference to post 17 of post in this category "DCOE fast idle problems" (I can't post links yet) I tried setting the idle adjust screws to 1/2 a turn. The rpms climbed to about 5000 before I shut the engine off out of fear of damage. Last week it was running at 2500rpms with the idle adjust screws out 1/2 a turn - I haven't changed anything else, so I'm starting to feel like I have no control over the engine.

Here's some background:

Weber jet settings (located in midwestern USA):
Venturi 32
Main jet 135
Air corrector jet 210
Emulsion tube F-34
Idle jet 55F17
Needle valve 150
Acc. pump jet 35
Acc. pump bypass 60

Fuel pump is a "E8016S", I thought it produced 2.5-4psi though some folks have shared their doubts. No fuel pressure regulator since the PO tore out the fuel return line :confused1:

Currently using air horns though I plan on adding a proper airbox and filter at some point. I have made sure the throttle linkage is not pushing on either throttle rod when the gas pedal is not depressed.

Any suggestions on how I can tame this beast? At first I could barely get the car started since it was sitting for so long, but now I can't get it under control. I'll try again tomorrow to see if it still wants to run at 5000rpm "idling"...
 

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Stating the obvious, the throttle stop is wound back and the butterflies are fully closed? If not adjusting the idle jet will make little or no difference.
 

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Or your distributor advance is to far forward. I would go back to the basics by starting with the covers for the idle circuit removed so you can see the butterflies and if they are aligned to the same hole. If not your balance is way off or your linkage is to short pulling the butterflies forward. I would get some WD40 and squirt around the base of the carbs and mounts to see if you have an air leak. did you put gaskets on both sides of the mounts?
 

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check that the enrichening device is not stuck open. I had a lot of trouble with my carbies after sitting for a long time. everything gummed up.

cheers ian
 

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Discussion Starter · #6 ·
Aggie57: Wow, I checked the butterflies and for some reason they were all open. I suppose I must have bent something by mistake, I'm not sure what happened but when I disconnected the gas pedal throttle line from the carburettors the connecting rod sits 1cm away from where it was connected - fixing this reduces the idle back down to a "normal" 2500-3000rpms at "idle" rather than shooting past 5000.

velocedoc: I have attached a picture of my advance curve. The first one is what I've been using so far, the second is an adjusted curve with a slower advance at low rpms and a maximum of 28 degrees rather than 38. I've heard of both as the maximum... the car says 28 under the bonnet but most forum references to max advance suggest 38.

I tried spraying oil on the intake around the rubber mounts - yes, both sides have gaskets - the oil just seeped into and around the joint. Should I be using gasket sealer on the gaskets or just the paper gasket alone? I'm sort of new to this, perhaps I should have asked before I put it all together.
 

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Jarred, sounds like you are on to the source of the fast idle; the bent linkage. Most times it is to short and the linkage will pull the butterflies just enough to allow more air in, hence raising the idle. A rough basic starting point to balance the butterflies is through the idle holes, and that they are fully seated before putting on any linkage or adjusting the idle screw. There should be no change in idle when you hook the linkage.

I have no clue what to tell you about the advance on your distributor.



This is what I use for most gaskets that need to seal. It is kind of like a low tack contact cement. I have been using this product for years. Put a thin coat on both sides of the gasket on the intake gaskets and you won't have any air leaks. Of course, there any number of sealants out on the shelf at any parts store, this is just what I choose to use.
 

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Discussion Starter · #9 ·
Thanks for the suggestion velocedoc. I'm going to rebuild the intake with some sealant on the gaskets tonight. Another issue I discovered yesterday: After disconnecting the gas pedal from the linkage, one of the carburettors is still not fully closed. [ame]http://vimeo.com/163737595[/ame]. Sorry for poor lighting. What you're looking at: the left carburettor throttle is being held open by the spring loaded right linkage and I can push it closed by hand. My thought for a solution is to remove the linkage and select a smaller spring (see attached). Is there a better way?

Alfar7: I have the 123\Tune distributor without the built in curves. I've tried to find accurate plots of the 16 built in curves of the non-tuneable version online to no avail.
 

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This is what I use for most gaskets that need to seal. It is kind of like a low tack contact cement. I have been using this product for years. Put a thin coat on both sides of the gasket on the intake gaskets and you won't have any air leaks. Of course, there any number of sealants out on the shelf at any parts store, this is just what I choose to use.
About 40 years ago a WWII aircraft mechanic showed me a simple little trick for the mounting blocks. Don't use sealant. Put a very light coating of multi-purpose automotive grease on the gaskets. I've never had air leaks and I don't have to scrap gunk off of anything if the carbs ever have to come off the car.

As a side note, for those who check in with mounting block issues, the quality of the rubber mounting blocks varies widely and not all of them have flat mounting surfaces. It pays to examine the mounting surfaces carefully before installing them, because the ones that come warped will never seal properly.
 

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Here is the curve Tom Sahines recommends as a starting point for the 123 Tune. I am using it and it works very well.

----------------------------------
A good starting point would be:

RPM LIMIT 6500 (or less if you are concerned about over revving your motor)

point 1 500 rpm 6 degrees

point 2 1000 - 6

point 3 2000 - 20

point 4 4500 - 38

point 5 8000 - 38 (dont worry this can never happen as the rev limiter
will be your actual maximum)
 

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Jarred, I would remove both carbs. I am curious to know if you have a bent throttle shaft. You can do this by comparing the butterflies through the idle air holes. Another way is to hold the carbs up to a light and look through the venturi and compare how much light there is coming through the butterflies. There should be little to nothing. Are the carbs rebuilt? When installing new shafts and bearings you have to remove the butterflies. If they are not aligned properly, you will not be able to get the carb to balance. There are a lot of things to learn and I am no expert by any means. Just offering some sage advice from what I have learned over the years.
 

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I don't think George Willet will mind if I share what he passed along to me years ago. It's copied below. This link is also well worth checking out: Daves home page

Care and feeding of your Weber carbureted engine.

First the carbs need to be synchronized:
• Back the idle speed screw out until it no longer contacts the arm; unscrew and remove the 4 plugs for the progression holes.
• Shine a good flashlight down into the port; slowly screw in the idle speed screw on the rear carb until you can just see the shinny edge of the butterfly through one of the three progression holes. (Some carbs may only have two progression holes per throat).
• Then slowly adjust the balance screw for the front carb until you can see the edge of the front carb butterflies though the progression holes in the same progression hole as the rear carb.
• Move the idle screw in and out a couple of times and watch that the butterflies on both carbs are in the same spot through the front and rear carb progression holes, if not then repeat the above sequence until they are in the same relationship as seen through the holes.
• If one butterfly of the four is “early or late” then the throttle shaft is twisted and needs attention.
• Open and close the throttles a couple of times: recheck; redo adjustments until they are exact!
• Use this method to balance the carbs: DO NOT USE AIR SYNCHRONIZERS, see below.
• Now back off the idle speed screw and then slowly make contact with the carb arm and give it ½ turn to just open the butterflies.

Initial idle set screw adjustment:
• On carbs with a two digit suffix, GENTLY close the mixture screws till they just seat and back out ¾ turn: on carbs with a three digit suffix, back out 2 ½ turns.
• Start the engine and set the timing, (see below)
• The engine should now idle around 900 RPM; if not adjust the idle speed screw until you are close to 900, but not faster. IMPORTANT. (You change the mixture requirement as the idle speed goes up and you will throw your adjustments off if the idle is set too high, and the engine will “hunt”).
• To adjust the idle mixture: turn out, (or in), the first screw slowly until the engine picks up RPM. If it speeds up over 900 RPM, then slow it down with the idle set screw and continue adjusting the mixture until it idles the fastest via mixture adjustment, but not over 900 RPM. (I don’t care what cams you are running, what porting, what exhaust, you should be able to get this idle speed, or something else is wrong ).
• Then turn the other three screws exactly the same number of turns. When you have it right all four screws must be adjusted off the seat the same number of turns, or fraction of turns.
• Adjusting the mixture at idle takes a minute for the engine to consume all the extra fuel from a richer setting (out). Give it a chance to settle.

Recap.
• The butterflies will be in exactly the same relationship to the progression holes on both carbs via a mechanical adjustment.
• The idle will be at 900 RPM.
• The idle mixture will have the engine running at the highest speed, but not to exceed 900 RPM.

Now:
• Turn in the idle mixture screws equally just a little to lean out the mixture.
• Bring up the RPM slowly once or twice to clear the engine, but not to make the accelerator pump inject too much gas.
• Set the idle mixture screws as lean as you can until the carbs spit back, or the engine stumbles when starting out on a drive with a warm engine.
• Turn out the screws minimally until the engine is as lean as you can go, but only spits rarely, and drives ok up to about 1500RPM. Beyond that you are in the idle jetting.
• You only run on the idle screw mixture up to 1500+- RPM.
• You should be able to slowly turn in the idle screw and the engine will respond smoothly.

Adjusting the ignition timing:
• With the engine warm, have someone using the timing light watch for the M mark to come up on the pulley, while you bring up the RPM until the distributor stops advancing. This will be anywhere from 3000 to 5000 RPM depending on the distributor.
• Rotate the distributor until the timing mark and the pointer align on the M mark on the pulley at maximum distributor advance.
• Snug the distributor down. Recheck the timing.
• Tighten down the distributor. Recheck the timing.

Notes on ignition timing:
• **Use the M mark on the two liter engines, you need to use a two degree timing loop to determine the correct advance for other engines**.
• (“Timing loops”: Slightly retard the timing a few degrees from what you have; accelerate in third gear on a level stretch of road using a set RPM range, IE 3500-6500 RPM or whatever range your engine works best in; advance the timing 2 degrees; accelerate over the same road; If you are faster, keep upping the timing 2 degrees until you feel the car going slower, or the stopwatch shows you have lost time between the selected RPM segments. When the car acceleration slows from the preceding adjustment, go back to the last setting where it pulled the best/ had the quickest time on the stop watch). (“Don’t do this at home ” unless you have what I call “mechanical empathy”, it is a matter of feel).
• The amount of advance in the distributor affects the idle speed and throttle response. It should be recurved by a good source that races Alfas, to match your engine set-up recipe. If the advance is less than 3 to 8 degrees at idle with the setting at the M mark, then you know your distributor needs help. Some race engines need 12/15 degrees at idle to run properly. Most of the Marelli distributor with the weights up, are sticky and worn, and give erratic settings until cleaned and the advance limited in the distributor. And the Marelli Plex distributors I have tested are all over the place on internal advance. The Bosche distributors off of the 1600 engines have too much advance in them for 1750/two liter engines and need to be limited on advance.



Notes:
Try to keep the engine temp near normal running temp while doing mixture adjustments, as this will affect the mixture.
• Jetting the carbs are a whole ‘nother discussion, and there are complete books written on the subject.
• All of the above came from “the” books, from the best West Coast Weber guru, and from my experience. There are other ways to accomplish the above, but this works.
• So, why not use air synchronizers? The air synchronizers reflect the volume of air entering each carb throat. This can vary depending on many factors: camshaft timing on each cylinder, (Auto Delta and the factory adjusted the lash according to the timing of each lobe, not valve lash dimensions); variations in spark timing per cylinder due to distributor pick up point variations; compression ratio variations between cylinders; port volume variations; mixture adjustments; etc). The Webers rely on the mechanical position of the butterflies opening each progression port in the same relationship to the others to meter the same air/fuel mix to each cylinder at idle speeds and up.
 

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Discussion Starter · #14 ·
Velocedoc: I got the carbs on eBay from a guy who removed them from one of his cars (a Ford Cortina for what it's worth). They were very clean when I got them and I re-jetted them as per specs in the opening post of this thread. The butterflies align and fully close (though they do not spring completely closed on their own) but it seems the throttle linkage pieces are not properly matched. I got them from an eBay seller who claimed they are redline parts and they arrived in redline packages, though I'm a bit suspicious. Upon close inspection it appears the rotational orientation of the squared off holes of each side of the linkage do not match, which is why one side is held open. I've made a small modification to allow adjusting the closed state in both directions - see attached photo. This weekend I'll try starting the engine without the linkage attached.

Gary: Finally clear directions on appropriate adjustment of a NEW weber carburettor setup! All references I've found so far don't go into detail about what you do immediately after installing completely unsynchronised carbs. I will definitely follow these directions and see where I get. Now I understand what the three holes are for too. Am I correct to assume I have to re-install the progression hole plugs before starting the engine?
 

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Jarred, if you don't put the plugs in, there is no way for the vacuum side to pull fuel through the idle circuit. Hence the car won't run. :D
 

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The credit goes to George Willet and Dave Andrews. I have the Weber manual, but prefer to follow the instructions from Dave and George.

My old unisyn (first used on a Healy 100 in 1964) and synchrometer now gather dust on a shelf with other stuff I no longer use but can't bear to part with.
 

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While your messing with the linkage and all if you don't have the Centerline bell crank I would sure get one. It is WAAAAY superior to the OEM crank, easy to install especially if y0u have carbs off. Will really smooth out throttle function.
It's the first thing I put on a new (old) Alfa upon requisition if it does'nt already have one.

Luck, Ralph
 

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Discussion Starter · #18 ·
I thought so, just checking.

I checked and re-checked everything and finally discovered two issues: my carburettors do not fully return to the completely closed state on their own, and when pushed fully closed, they "pop open" - in other words, I need some sort of long lever attached to the throttle with a spring holding the carbs closed. Has anyone encountered this issue before? How should I go about solving this issue?

I believe an appropriate approach to a solution is an external secondary throttle return to serve as a "helper" mechanism. The best I could find is on eBay here. For good measure (and since this issue effects both carburettors) I would like to install two, one on each carburettor on the opposite side of the linkage. The kits I found are $30 a piece, seems a bit much for a spring and a bit of sheet metal. Any thoughts on where else I might find the same mechanism? Photo attached in case the eBay page is taken down at some point.

I've also attached a few photos taken of the inside of the throttle body on one carburettor. There is brown fluid covering these areas, looks like gasoline has sat in this area for a while. Is this a problem?

Here are a few videos of the engine running and the throttle return mechanism to illustrate my progress. When I purchased the car it was a frame with an engine and transmission, absolutely nothing else. It's gone a long way since then! Thanks for all your help so far.
 

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Discussion Starter · #19 ·
Aside: Is there any way to post a link to a video without it being automatically embedded in the post? I can't for the life of me figure this one out. Sorry for the readability issue it causes.
 

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You have an internal issue with the carburetor. You should not need any kind of a return spring to pull the carb closed. When the linkage is hooked up properly with a good return spring on the pedal mechanism that attaches to the fire wall, that should be enough to pull the carbs closed. Even so on the bench the carbs should pull closed enough to go past the 3 idle holes. Internally there is a spring that pulls the butterflies closed that is part of the accelerator mechanism. When you push on the pedal, the mechanism pushes on a piston that pushes fuel into the advancement circuit for lack of a better description. When you take your foot off the pedal the spring internally resets the accelerator piston and closes the throttles. The only other thing that could be is the rods are bent from being pushed to far bending the end of the rod where the attachments go on. The other is that the bearings are frozen and not letting the butterflies seat.

You should be able to pull the venturi's out, and the other part that is in there. Clean everything and see if that helps close the carbs.
At this point I would send them to Gordon Raymond for rebuild if he has the time.
 
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