Dual carb question, Dellorto 40s on a 1.8L to be exact Options

[rhodyguy]

the linkage ABOSOLUTELY comes into play when the idle speed adj screws are resting on the stops. when sitting static, a misadj linkage can push/hold one side open further than the other. just one of the screws resting against its stop will control the idle speed. they do cease to have any effect when the carbs are open to the point where they are both off their stops. if the throttle plate openings are unmatched whether at idle or wot your car isn't going to run right. you want to make sure everything is connected when the side to side flow is matched at the base, common step up.

k

[type11969]

Wait, if both idle speed adjusting screws are resting on their stops, how can the linkage hold one side more open than the other? Both screws are resting on their stops. When sitting static, the linkage should not be applying a twisting force to either butterfly! If you are suggesting that the linkage is holding one screw off the stop while the other is on, well, your linkage is out of adjustment and, obviously, both screws are not on their stops. If you spin the one screw that is not on the stop to meet the linkage then the flows are no longer balanced.

If you match the flow with the linkage disconnected (idle speed screws fully seated on the stops), then you connect the linkage such that it matches the butterfly positions of both carbs throughout the rev range, the flow will be matched throughout the rev range. I don't know how else to explain it. The linkage's only function is to make sure that both butterflies are in the same place at the same time, it should not be used to match the flow of the two carbs at any one point, because at any other point it may no longer be matching the flow.

the linkage ABOSOLUTELY comes into play when the idle speed adj screws are resting on the stops. when sitting static, a misadj linkage can push/hold one side open further than the other. just one of the screws resting against its stop will control the idle speed. they do cease to have any effect when the carbs are open to the point where they are both off their stops. if the throttle plate openings are unmatched whether at idle or wot your car isn't going to run right. you want to make sure everything connected when the flow is matched.

k

[rhodyguy]

ok. linkage off. flow set the same side to side with the idle adj screws. now attach the rods with one of them longer than the other and touch nothing else. check the flow rate now!! a c-note says it's off. flow is flow. with the throttle plate opening the same at idle it will be, or should be, the same throughout range of operation

on a side note, not all webers are 'built' the same. some have 'helper' springs on the outside of the throttle plate bars and some don't. w/o the helper springs, linkage disconnected (this means no cable return spring), start the car. bottom line, do what works best for you. my method works swell for me. my carbs don't snap or pop, nor does my car backfire on decel.

k

[type11969]

Well, if one rod is longer than the other and it forces the throttle plate open on one side, then the linkage IS NOT adjusted properly, now is it? It is interfering with the initial settings and should not be. Obviously the flow will be different because one plate is open more than the other (thanks for the really tempting wager though). It would be at this point that I adjust the linkage such that the idle screws are resting on their stops (matching the initial sync), then I would verify that the butterflies both open fully and at the same rate.

What I am doing is setting my linkage about my initial position. What you are doing is setting your initial position about your linkage. Which one takes more fiddlin I don't know.

Snapping, popping, or backfiring usually is not a sign of a poorly set up linkage, but I am glad your car doesn't suffer from any of those maladies.

-Chris

ok. linkage off. flow set the same side to side with the idle adj screws. now attach the rods with one of them longer than the other and touch nothing else. check the flow rate now!! a c-note says it's off. flow is flow. with the throttle plate opening the same at idle it will be, or should be, the same throughout range of operation

on a side note, not all webers are 'built' the same. some have 'helper' springs on the outside of the throttle plate bars and some don't. w/o the helper springs, linkage disconnected (this means no cable return spring), start the car. bottom line, do what works best for you. my method works swell for me. my carbs don't snap or pop, nor does my car backfire on decel.

k

[Joe Ricard]

So what are we betting here?

What Kevin is saying is pretty good to get you in the ball park.

However if you really want to be precise you should adjust the linkage one step further than stated above.

now that you have the idle stops adjusted there is no promise of the throttle plates being synched up once you push on the gas pedal.

The machining of CB linkage and several others is just not that accurate. What you are dealing with is differing length from throttle shaft to the point where your spherical bearing linkage arm connects.
I have had to slot one or both arms to match up the mechanical advantage so the throttles stay perfectly synched thru the entire arch of movement.

Then I always set the throttles to be synched at 3000 RPM pulling on the cable and using a synch tool. Close enough is not good enough for me.

Once I get this far I let the linkage settle back on the idle stops and see where they sit synch wise. you can now adjust them perfectly while leaving the linkage alone. Most CB type linkage has enough slop to allow this.

I have a Billet custom piece that is very tight. if you breath on one side it moves the other.

[rhodyguy]

i'm glad you see what i'm getting at joe. my method just eliminates a step or 2. with the off stop side hanging, you either tighten up or loosen the rod to match the other carb. you can really make minute adjustments. i don't give a shit what one idle screw is doing at this point as long as it's not 'in the way'. it's removed from the equation. when all is said and done, the backed off screw is run in til' it just makes contact and starts to increase the idle speed then off a bit. increasing the idle to stop the indicator in the unisyn from fluctuating is VERY important. you increase yours more than i do. i go just enough to steady the needle. if it dances even the least istsy, bitsy, teeny, tiny bit, i turn the idle up. as stated...do what works best for you. (IMG:style_emoticons/default/wink.gif)

k

[type11969]

The bet was if you sync the carbs with the linkage off (idle screws on the stops) that if you attach the linkage, and the linkage is set such that it pulls one of the idle screws off the stops, that the carbs would not still be flowing at the same rate. Hmm, still debating if I should take it (IMG:style_emoticons/default/blink.gif)

Anyway, "my" method works fine, and I believe it is how most VW guys do it. Here is a more in-depth explanation if you are interested:

http://www.aircooled.net/gnrlsite/resource...es/dualcarb.htm

[BxtrBill]

Are you sure, or is it possible to put the in upside down, so that the numbers are at the bottom? I took a flashlight and stared at them for about 5 minutes and couldn't see anything.

Hm..hadn't considered someone might put them in upside down, but it's entirely possible to do so. I can't say what to expect from an upside-down venturi, but I'd be fairly certain the carb(s) wouldn't work as designed....I'd guess it would upset airflow by moving the low-pressure area of the venturi lower in the carb, but I never tried it so don't know what to expect. Before you do anything else, it may be worthwhile to check one more time for the numbers.....they're small, but they *should* be there. If they're not, someone has reversed the vents in the carb body, maybe the same guy who "drilled out" the emulsion tubes (hint: don't ever do that) Emulsion tubes, in concert with the air correction and main jets, control mixture in relation to airflow. E-tubes are available to lean or richen the mixture at different spots in the rev range, but generally you're best off with the tubes that came with the carbs. You should be fine with 180 airs, too....you can go to 200s and that will have the effect of leaning the mixture slightly across the range, but to no real advantage.

It's easy to remove, then reinstall the vents correctly. Remove the air cleaners and the top cover of the carburetor. If you're really brave, do this while the carb is still on the engine. I'm not that brave, so I do this on a bench. There is a set screw with locknut at each end of the carb body....loosen the locknut, then the setscrew, and remove the aux (boost) venturis, then the pump jets. If the carbs have been cleaned recently, the main venturis should slide right out...if not, they may take a bit of gentle persuasion. Nothing drastic, please...they're just potmetal. Stick 'em back in with the numbers toward the top side of the carb, and screw everything back together. Or as the Haynes says, "Assembly is the reverse of disassembly"

One thing I'd add.....when you're trying to troubleshoot something like this, Change One Thing At A Time. Focus on one part of the problem...the idle....midrange, transition, high-speed running, acceleration, etc, insofar as possible. Carb functions overlap, granted, but it's a real booger to guage the effects (if any) of a change when two or three things changed at once. Ok...off the soapbox now, and you probably knew that anyway.

[terrymason]

I'm working in Seattle all this week, so won't get to make any changes to the car, but I did snap off a few photos before I left.

Here are my etubes, and a shot down the mouth of one of my carbs. Just so that I'm not loosing it, the main venturi is the large sleeve that the red arrows are pointed at right?

[terrymason]

etubes

[type11969]

Looks like at least that one etube had one of the proper holes soldered shut at the top, check to make sure that is the case all around.

Yes, that is your vent.

-Chris

[Joe Ricard]

Them aren't webers are they.
At least they look nothing like either my 40 or 44 IDF's

[BxtrBill]

Here's a pic of the venturi out of the carb....the one on the left shows the number (with a bit of highlight...they can be a booger to see) and is "right side up", or the way it would be installed in the carb. The right one is upside down and you can see the fairly pronounced radius on the bottom end. This would be nearest the throttle plates when installed.

Of course it's always possible someone removed the numbers.....there's a fun thought.

[terrymason]

So, there's a blunt end, and a tapered end? Thank you very much for the photo. I've ordered some 30s (even though I'm not exactly sure what I currently have). I'll install them when I'm back in town, and verify that everything is pointed in the correct direction.

[Twystd1]

I just went through this with some other 914 bretheren.

You will NEVER get the carbs dialed in right with an 009 distributor.

Unless you have the 009 dialed in and curved PERFECTLY for a type IV engine. And I don't care if you have a crane, points or Pertronix in it.

Nobody believes me until they stick in an stock type IV or Mallory distributor.
Then re-dial in the carbs and the engine runs right for the first time.

Many companys sell a 009 dizzy supposedly setup for the type IV engine.
So far... In my experience.... It's total bullshit.
I have yet to see a 009 from any company that is correctly curved for a type IV engine. They suck... Toss it. A used bone stock dizzy is better.
And you won't be tuning your carbs around a screwed up ignition curve and inaccurate dwell.

Try it... You will like it.

I gave my last three stock dizzys away just to prove it. As these three guys had the much of the same carb tuning problems. Once the correct ignition curve was there for the type IV. The tuning issues were much easier to fix.

That is my experience. Yours may well be different.

Regards,

Clayton


PS: I hate 009 They are a bane to the 914 society. There ought to be a law against em in the type IV world. That goes for progressive webers as well.

[Joe Ricard]

That' odd having the blunt end of the Venturi on the inlet side.
Weber carbs have the taper on top. which makes more aero dynamice sense.

[type11969]

I'm pretty sure that is reversed, I'm almost 100% sure the vents in my dells are installed with the radiused edge pointing up.

[BxtrBill]

I'm pretty sure that is reversed, I'm almost 100% sure the vents in my dells are installed with the radiused edge pointing up.

Quite right...don't know what I was thinking (or IF I was thinking) about the radiused edge. Turns out *some* OE Dell vents have the number on the radiused edge and some have it on the "straight" end. Checked the ones in the white car (Dell 40s) and they're right up top on the radius.....checked a still-in-the-box set of Weber 44IDFs and they're in the same place. Checked the 40IDFs on the blue car and, sure enough, the number is on the radius. Sorry for the confusion.

[terrymason]

I'm back in town, and had some time to look at my Dells. I took out the venturis, and I was finally able to find a 34 etched by hand on one end of each. It looks like they were larger, then were milled down.

I'm still waiting on my new 30 venturis. and will report back when I get them

[rhodyguy]

i think your car is going to perform vastly better running a set of carbs with smaller venturis.

k