Hey all you dual carb guys!
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Thread: Hey all you dual carb guys!

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    Hey all you dual carb guys!

    So I got my engine in and my transmission stuff all figured out thanks to all your help. And now I am needing help once again. So I am running dual Weber DCOE 40's and and in the process of tuning them. I borrowed a synchro-meter from my friend to try and balance the carbs, but here is the problem.

    When I put it in one carb (the one furthest forward on the car) it reads normally at around 6 or something. When I put it in the other carb it pegs down at 30. I have tried adjusting the the balancing screw and it doesn't change. I checked the butterflies and they are functioning correctly.

    As advised by RallyBob, I have drilled and tapped a runner on each carb and connected them to run the brake booster and vacuum advance.

    Any help you can offer would be great. I have tried timing it TDC and a few degrees advanced.

    thanks,

    -Aron
    Last edited by tekenaar; 02-25-2012 at 08:23 AM.

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    When I adjust the carbs on my Alfa I don't use any equipment at all, I'm not saying you won't get better results with proper equipment but you should be able to get it in the ballpark without it

    First make sure your static timing is thereabouts at least

    Second, close the butterflies completely. Ideally your car should idle on closed butterflies allowing you to adjust the idle with the idle mixture screws

    Third, set the idler mixture screws at 2,5 turns "out". That's about as rich as it should need, the ideal setting is between 1-2,5 turns but you can go further if needed

    Now fire her up and hopefully she'll run without needing to adjust the opening of the butterflies and listen to how the engine is running. If it's running really rough and the engine is shaking your carbs aren't balanced, adjust the balance screw until you have a reasonably smooth idle, adjust the opening of the butterflies as needed to keep the engine running but remember that the balance screw will also affect the opening of the butterflies depending on which carb is is more open than the other since they're linked (I think you're understanding what I'm saying even if I'm not explaining it too well)

    The next bit is where you use your sync meter or do as I do, pop off one spark plug at the time and listen for the drop in engine revs, or have someone look at the tach while you're working. Adjust the butterflies so your engine is turning 15-1800 rpm so that it's no longer running on the idling part of the carb. 1 and 2 should ideally be the same drop as should 3 and 4 and with a bit of adjusting you should be able to get the drop in revs even across all 4 of them. Make sure you don't lean against the car as you're popping off the plug wires and wear gloves ..... if you have a heart condition have someone else do it for you

    Once you have the carbs synched close the butterflies again, preferably all the way but at least to where your engine idles at the revs you want and repeat the procedure across all 4 cylinders with the idling screws on each runner. I usually aim at 1,5 turns but on my Alfa I have to keep one cylinder at 4 turns, it's a bit down on compression on that cylinder and the plug is oiling up a bit and giving it a bit more fuel seems to make it happier around town

    Btw, if you have *any* vacuum leaks you'll be chasing your tail on the adjustment, buy a can of starter fluid and spray liberally around where the carbs and intakes are joined and listen for any rise in the engine revs and a give a little squirt in each runner too just to make sure it's actually firing on that cylinder if it's running really rough
    Last edited by tekenaar; 02-25-2012 at 08:25 AM.
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    Quote Originally Posted by OpelWagonGT View Post
    As advised by Rallybob I have drilled and tapped a runner on each carb and connected them to run the brake booster and vacuum advance.
    For tuning only, cap off these individual runners. If the signal is shared the synchrometer can't differentiate from cylinder to cylinder.
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    Quote Originally Posted by RallyBob View Post
    For tuning only, cap off these individual runners. If the signal is shared the synchrometer can't differentiate from cylinder to cylinder.
    Oh snap that makes total sense now! So just for tuning purposes I need to remove and cap all the lines so the carbs are isolated. Haha thanks.

    Correct me if I am wrong too but the carburetor "balancing" screws are just the ones on the throttle arm that push it open as you screw them in right?


    -Aron

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    Quote Originally Posted by OpelWagonGT View Post
    Correct me if I am wrong too but the carburetor "balancing" screws are just the ones on the throttle arm that push it open as you screw them in right?


    -Aron
    There should be two screws there, one that goes through a hole in one of the carbs and pushes on the throttle arm, then there's one that goes through one throttle arm and pushes on the other arm

    The latter one is used to sync the carbs, "zeroing" the shafts to each other, the first one is used to open/close the butterflies to adjust the idle in case your engine doesn't run with the butterflies fully closed
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    Oh ok I know what you are talking about. The linkage that my carbs have don't have a screw that does that . The linkage arms clamp onto a shaft and you can tighten them via allen wrench.

    -Aron

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    Quote Originally Posted by OpelWagonGT View Post
    Oh ok I know what you are talking about. The linkage that my carbs have don't have a screw that does that . The linkage arms clamp onto a shaft and you can tighten them via allen wrench.

    -Aron
    Okay, I'm not familiar with that kind of linkage so I'm afraid I can't help you there
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    So,

    I have given up tuning my car myself. I think I need to seek professional help. I have timed and re-timed and done all kinds of stuff and cannot get it to run correctly. It idles rough and just totally loses power at the top. It pops sometimes. The idle won't go down. It's too much for me and beyond my realm of knowledge. So if there is anyone you know in the Seattle area that knows how to tune dual carbs I would love to talk to them and possibly pay them to do it. Of course I guess at this point it isn't just the carbs but tuning the engine too.

    -Aron

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    Project 1450 supporter... Site Supporter My location RallyBob has a spectacular aura about RallyBob has a spectacular aura about RallyBob has a spectacular aura about RallyBob's Avatar
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    Quote Originally Posted by OpelWagonGT View Post
    So,

    I have given up tuning my car myself. I think I need to seek professional help. I have timed and re-timed and done all kinds of stuff and cannot get it to run correctly. It idles rough and just totally loses power at the top. It pops sometimes. The idle won't go down. It's too much for me and beyond my realm of knowledge. So if there is anyone you know in the Seattle area that knows how to tune dual carbs I would love to talk to them and possibly pay them to do it. Of course I guess at this point it isn't just the carbs but tuning the engine too.

    -Aron
    Try contacting this guy: JVAB Imports

    He's a bit ornery and very opinionated and will talk your ear off if given the chance. But he knows performance rally and racing 4-cylinder stuff and has worked on Opels for 30+ years.

    Phone is the best bet, he barely ever does email.
    My Flickr photos.
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    Quote Originally Posted by RallyBob View Post
    Try contacting this guy: JVAB Imports

    He's a bit ornery and very opinionated and will talk your ear off if given the chance. But he knows performance rally and racing 4-cylinder stuff and has worked on Opels for 30+ years.
    Sounds like my kind of guy.
    Nice stuff that he's worked on...drool
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    Quote Originally Posted by RallyBob View Post
    Try contacting this guy: JVAB Imports

    He's a bit ornery and very opinionated and will talk your ear off if given the chance. But he knows performance rally and racing 4-cylinder stuff and has worked on Opels for 30+ years.

    Phone is the best bet, he barely ever does email.
    I might try contacting this guy. Thanks! Problem is though if he wants to look at it then I need to get it to Seattle somehow.

    -Aron

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    Aron,
    U-Haul!
    Take Care,
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    haha this might sound stupid, but my car was idling rough and had no power and would pop i thought it was the carb but then i realized that i accidentally crossed crossed two wire on the distributer haha.. just suggesting u take a look at that before u go crazy!

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    Quote Originally Posted by rocknroll View Post
    haha this might sound stupid, but my car was idling rough and had no power and would pop i thought it was the carb but then i realized that i accidentally crossed crossed two wire on the distributer haha.. just suggesting u take a look at that before u go crazy!
    I seriously hoped this morning that the problem was crossed wires but I double checked. But on the good side of things I apparently should have re-setup my electronic ignition when I put the motor in this car according to my dad so I'm going to try that.

    -Aron

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    Well I did check the phasing on the distributor and that made it better. I also figured out the reason that it wouldn't idle low enough was because my throttle return spring was not strong enough. I feel like I need to take the carbs apart, clean, and put them back together.

    Now it just idles rough and still has no top end power. Occasionally when you press the gas and let off the RPMs won't drop down.

    -Aron

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    So I took a video so you guys can see what's going on. It seems like for some reason the throttles don't close all the way unless I pull up on the linkage. When I let go the RPMs rise up.

    http://youtu.be/2qmYAL36BQ0

    -Aron

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    So I just finished re-assembling the carbs after cleaning them. I notice in the process that the venturi tubes are all stamped 45. Is this normal for these carbs? On the bodies they are stamped 40DCOE18. Also the chokes are stamped 30.

    I swapped the throttle arms and I'm going to try switching the carbs position to see if the difference in vacuum is related to the carbs or the engine/intakes.

    -Aron

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    Quote Originally Posted by OpelWagonGT View Post
    So I took a video so you guys can see what's going on.

    http://youtu.be/2qmYAL36BQ0

    -Aron
    Nice video Aron.
    It sounds like number four exhaust valve is not opening properly.
    Black Horse

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    Quote Originally Posted by OpelWagonGT View Post
    So I took a video so you guys can see what's going on. It seems like for some reason the throttles don't close all the way unless I pull up on the linkage. When I let go the RPMs rise up.

    http://youtu.be/2qmYAL36BQ0

    -Aron
    It does sound as if your carbs are out of sync, which means that when one carb is closed the other one is still partially open and keeping your revs up, when you're pulling up on the linkage there's enough "give" in it to let the second carb close and your revs drop and then it rises again when you let go of the linkage. That "helicopter" sound and the engine shaking like that are signs of cars that are out of sync

    If you've managed to identify how your carbs are synced just adjust one way or the other until you hear a difference, overdo the adjustment so you can tell what happens when you turn the screw(or whatever) one way or the other, just make sure you always make a note of how much you're adjusting it so you can go back to your baseline setting and start over, I *always* count how many revolutions I'm adjusting *anything* on my carbs.

    You *will* get confused while you're working on this stuff so making notes of what you've done is essential
    Last edited by ggl; 02-22-2012 at 12:36 PM. Reason: added more text
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