The problem - The car will go very lean around 2500 rpm, as if the pump jets were too small.

History:
New fuel pump (3.5 PSI to each carb)
55 idle jets
55 pump jets
140 main jets
175 air correctors
These carbs are new to the car, and I'm trying to dial them in.

The car is lean when I first start it (16 / 17 on my air / fuel gauge), but then levels out to a nice 14.7 idle when warmed up. While driving, I can give the car 20% or so of the pedal, and drive up to highway speeds nicely, but when I goose it, it will go very lean (18-22 on my gauge) followed by a series of backfires and loss of power. I started off with 35 pump jets, and have moved up to 55s, which appear to be the most popular around here. I've also adjusted the pump jet linkage, from the nut fully loosened, and moved it in as far as it would go before affecting the main throttle shaft (like 60 turns or something).

What do you guys think, do I need 75 pump jets?

Send JR91472 a PM. He has a 1.8 w/ dual dell's, and could probably tell you what he's got in his.

40 Dells were usually equipped with 34mm venturis from the factory (hence the urban legend that 40 Dells flowed like 44 Webers which were also equipped with 34mm vents, but I digress)

The pump jets you have, being 55s, are probably enough to flat drown a 1.8 if you blip the throttle real quick a couple times. Just for reference, I've got 40 Dells on a 2056 with 30mm vents, 125 mains, 60 idles (CA gas, may it reek) and *40* pump jets. I could probably do with 35s just fine, but the 40s work, so they're staying. Your problem, whatever it is, is NOT due to the the size of the pump jets....the pump jets' function is to meter fuel when the accelerator pumps pump. They have nothing at all to do with steady-state running.

If I had that problem, I'd probably be looking at the idle jets first. Good rule of thumb is, most engines will run on the idles up to about 3000-3500 RPM or so. A plugged idle jet can make lean conditions, and the Dellorto design has them located where they can pick up any crap that makes it through/past the air cleaners.

HTH

I've tried quite a few idle jets from 46 to 60. I really don't think that the idle jets are clogged though, as I seem to change them constantly (just changed them from 52s yesterday). Just to be sure, I'll put my 60s in tomorrow.

You make a good point bringing up the venturis though - I have no idea what size mine are. I went into the garage and tried to check, but it looks like I'll have to take the carbs off the car to find out. Would the wrong size venturi cause these problems?

The problem is that dellortos suck. Sorry if you love them, but I have thrown three pairs in the can. I stick to Webers. Hope you figure everything out.

Speak for yourself on that one. Dellortos have always worked better than Webers for me.

When you have the carbs off the car fill the bowls and measure the volume of gas pumped out in one stroke of the throttle shaft. Then compare that throat to throat. I'll bet you've got something clogged, or your pump linkage either isn't right or isn't balanced side-to-side.

Terry-

You shouldn't be running that lean at startup or at idle . . . Im running 11.5:1 at idle, too rich for sure and I need to back it off, but 14.7:1 is only theoretically ideal, you need to be running in the 12 to 13 range (or less) for your car to be happy. 14.7 maybe on the highway, but talking to Charles at LN, he only sets up cars with Nickies that lean.

Right now on my 1.8 I have basically your same setup except with 180 airs and I am running 32mm vents. Check your vent size, if they are monsters you need to swap them out. I would actually rather be running 28mms, they may kill some top end but I know they would be more responsive than the 32s. You may want to swap out your airs, also check that you are running .2 etubes.

As for why you are running so lean when I have the same setup, well maybe due to vents/airs/etubes, but at idle I question that they would have that much of an effect. It seems like you either havea plugged idle jets or passages.

-Chris

OK, I have made some big headway on this. I pulled all the jets from the car, and blew them out with carb cleaner, along with the places they go. Replaced my 52 idle jets with 60s.

I think cranked the idle up to 2500, and used my unisyn gauge to check the flow. The passenger was a 5, while the driver was at 12. I adjusted the linkage so that they are both at 11 around 2500 rpm.

I then addressed my mixture, making all screws 2.5 turns out.

I then adjusted my pump jets. turning them about midway out. They were previously all the way tightened (I was trying to get a larger pump squirt)

I finally closed all my air bypass screws.

Now, the car idles around 10.5 a/f (probably from the 60 idle jets). It drives 100% better, but still goes lean when it starts to pull (2nd gear feels it most). It also seems that if I goose the gas it will go lean.

Sounds like your venturis are too big for a smooth transistion from the idle circuit
to the main jets.

Ok...you got me on that one. The pump jets sit in holders that screw into the (outboard) side of the carb body.....there IS no adjustability, except to replace the jets with larger or smaller ones. Are we talking about the same jets here?

Your initial mixture screw setting is probably good for a starting point, and the somewhat "fat" idle mixture makes things less picky when you're trying to get a new carb set-up sorted out.

34mm vents still sound kinda huge to me for a 1.8, though....28mm would be more like it. An over-carbureted engine does not respond well to minor jetting changes. They sort of gasp and stumble and generally run poorly except at one magic combination of throttle setting and RPM. If it were me, I'd go to www.cbperformance.com and see what they have in the way of jets and venturis for the Dellortos. Used to be they carried a bunch of stuff, but they seem to be more into aftermarket FI these days. You may want to order up their Dellorto Book, if it's still in print. It can be helpful, especially if this is your first foray into carbs. Another possibility is European Motorworks in Hawthorne, CA...don't know their web address offhand, but Google does.. They carry a bunch of Dell (and Weber) parts.

And a couple other questions for you......have these carbs EVER worked correctly on this engine? Or, failing that, do you know anything of their history, as in, what were they used on? It sounds like they have an as-shipped set-up, so I'm just wondering. There are dang few NOS Dells floating around these days, so yours probably did time on another engine before you got them...if you bought them from a friend who used them, maybe he'll be able to shed some light on things?

One more question....what was the reason for going to carbs in the first place?
If it was to replace a cranky FI installation, was the engine otherwise in good shape? Good compression...good tune-up specs...timing, valve adjustments, etc?
I'm curious, too, to learn what you're using for a distributor. Lotsa carb guys just stick in a 009 and call it good, and suffice it to say there are whole WORLDS of things that work better than those. The stock dizzy for a 1.8 isn't a bad choice, but it might benefit from some changes to the advance curve.

Sounds like you're making progress, though. Keep us posted.

Did you ever check out the vent size?

You should not be adjusting the linkage to balance the carbs, the carbs have to be balanced with the linkage disconnected. Once balanced, the linkage gets reconnected, and you try to make sure both carbs open and close at the same time and at the same rate.

Once at highway rpms, are you still running lean? Or only when accelerating? If it is the latter, it could be due to oversized vents but you may be able to correct for it with the pump shot. Verify your vent size, consider jumping up to 180 airs, and check your e-tubes. You also should try to measure your pump volume, you should gun for at least .2 ccs per two pumps.

The smallest vents CB had as of a month ago were 32s, they will be better than 34s for you (if you actually are running 34s).

-Chris

[/quote]The smallest vents CB had as of a month ago were 32s, they will be better than 34s for you (if you actually are running 34s).

The vents for the 36mm Dells also fit the 40s (same carb body), and you can get them down to 28mm at least. Just a thought. Can't say if CB has them, though.

Oh..almost forgot.....if you look down the carb throat at the top edge of the venturi, you'll see a number that indicates the venturi size.

- below the pump diaphram there is an adjustment (nut on a rod). I was under the impression that adjusting this changed the volume that was produced by a single squirt of the jet. I believe that I'll have to take the carbs off, and measure a squirt to make sure it's accurate.

As to the history of the carbs, I am replacing a single progressive carb with these dual dells. I purchased them fully rebuilt, and have been fighting a learning curve the whole time. I thougth that I would just bolt the on and go, but have ended up learning alot about the carbs. I'm currently using an 009 that came with the car.

Thanks for all the help - I'm about to go out of town for the week, so it will be a while until I can work on it again.

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.

Haven't checked the vent size yet.

I balanced the carbs with the linkage off, and everything was cool. They would idle and flow the same. I then hooked the linkage up, and it appears that the linkage to the passenger was longer, so that they were fine at idle (the speed screw kept it open), then when I revved the engine, the driver side would be opened further. Does that make sense? I think I just had some slop in the linkage.

once at highway speeds I'm fine. I am probably rich at idle and rich on the highway, but whenever I press the pedal quickly I go very lean for about 3 - 4 seconds, along with hesitation. The engine then levels out and is fine.

I've ordered some 185 and 200 airs, and have checked the emulsion tube. I have a 9164.1 tube, but the guy that sold them to me said "I drilled them out, so they are they same as the 9164.2". Does that sound right?

You gotta try to adjust the linkage such that the linkage opens the butterflys at the same rate and opens/closes them at the same time. That way you know they are sync'ed throughout the rev range. Syncing them with the linkage on at 2500 rpm probably means that they are only synced at 2500 rpm.

The accel hesistation may also be due to the 009. Its a pretty crappy dist. It is more likely to be due to large vents and maybe a small pump shot (you are right about how to adjust it). Try to measure the volume, make sure both sides are balanced and close to .2ccs per two strokes.

I'm pretty sure the dell manual recommends 180 airs for most applications, you could order the reamer kit and open up your 175s. I'm not entirely sure how the airs come into play in the whole scheme of things, but messing with it may clear up that transistion problem you have.

You can't "drill out" a .1 to a .2. You have to plug certain holes. I went through this ordeal with some poorly modded .1s that were supposed to mimic .2s. There are two upper holes you have to plug in order to get the .1s to be close to .2s. The raised middle band of the .2s is slightly larger than the .1s, but at 20+ dollars a piece, I'm getting by with the plugged .1s.

These pics should give you an idea about what has to be plugged. Hopefully whoever "drilled" them didn't actually drill them!

Click to view attachment

.1, .2, .3, .4

Click to view attachment

Going lean at 2500 probably isn't a function of accelerator pump.

I don't know Dells, but with Webers you are right at the transition between the idle and main jets.

i disagree with the "you should not be adjusting the linkage to balance the carbs" comment. by balance i presume you mean same rate of flow. you need common initial settings across the board. air bypass (closed or open), idle air mixture screws...the angularity of the linkage arms and drop links should be as similar as possible. if you have both of the idle adj screws making contact with the stops, and the linkage is out of whack, you'll prob notice difficulty sustaining a stable idle with an equal indicated flow rate. back one of the idle screws of its stop. this will allow you to match the 'free' carb flow to the other by simply turning the thread linkage rod in or out while monitoring the most forward venturis on either carb. you can increase the idle speed with the single screw. now check all 4 vents. this is where the air bypass screws come into play if there is a discrepancy. turn the idle back down. adj the idle air mixture screws. you need to be patient. a little adj can take a long moment to have full effect.

you need to inspect your linkage if the flow rate is constantly changing thru the range of motion. worn heim joints that rattle around and just plain slop makes setting the carbs up a hopeless and frustrating task.

k

This is what I mean. Linkage disconnected, pull out the unisyn or preferably the scroll type balancing tool. Match the flow rates of both sides by adjusting the idle speed screw. Match the flow rates of all the barells with the idle air bypasses (if you really want to be sync'ed). Put the sync tool away, the linkage cannot and should not be set up such that it will mess with the syncing of the carbs, it should be set up such that it maintains the initial sync. Connect the linkage such that the butterflys open and shut at the same time and the same rate. You will need to mess with the length of the linkage and may need to shim it to get the angles to match from side to side. Now, with the flow rates the same through the rev range, you can mess with the mixture screws to dial in the fuel for each barell.

The linkage does not come into play when the idle screws are touching the stops. If you synced the carbs properly, the flow rates of the carbs will be the same at any throttle position if both carbs are open to that same position. The catch is whether or not the linkage is opening the carbs up to the same position at the same time.

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

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.

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

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

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.

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.

k

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

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

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.

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?

etubes

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

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

Click to view attachmentHere'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.

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.

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.

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.

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.

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

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

k

Agreed, it "should" pull better down low.

And you will probably not run out of power all the way to 5800 RPM.

Above that and you need lots of internal engine work anyway.

Clayton is spot on regarding the dizzy. Go stock with the vac advance connected. I also upgraded it with the Crane Fireball ignition system.

I have hardly touched the carbs since....

your next decission is which intakes to run. i posed the ? re short vs tall for a f.i 2.0 engine and 40idf. len hoffman said to go with the talls for better top end performance. better power down low with the short intakes. my car is more of a highway runner. i went with the talls. keep us updated with your results. too often, we never hear the end of the story.

k

Yes please. I want to hear how the 30 vents work. I went with 32s on my 1.8L / Dell combo. Runs really really well, but if 30' are better

You might want to order some smaller main jets while you're at it....those 140s are gonna be way on the rich side, especially with the 175 airs. Rule-of-thumb says 120s should work...125s may be better. Too lean typically ain't good.

Hey rhodyguy. I think you may have the manifold info backwards. I heard tall manifolds for low and midrange performance. Creates more port velocity.

Mike

well, I've made alot of progress! I have installed new 30 venturis, and re-adjusted the linkage (one side was about vertical, while the other was a an angle). The car no longer backfires, and runs much better, but it does still go lean when switching from idle to main circuit.

I noticed that the auxiliary venturi (the tube over top of the main venturi) don't all match. 3 of them have the number 2 stamped on them, while one has the number 1 on it. I'm assuming that this is a measurement of some sort right? What size should I want? Any idea what this would cause?


Thanks guys! It's great to have my car running again!

You can actually see the aux venturi below

Not to hijack but I have 40 IDF's with an 009 dist. If I put the factory dist back on where do I port the vacuum from. Can I use one of the ports at the base of the carb? Do I need to connect the ports from both carbs together to keep the flow through them the same? I am also having some backfire issues and the motor seems flat when accelerated hard in the 3500+rpm range.

I remember hearing that the best stock dist to run is the 1.8 with the vacuum pot connected. Can anyone back this up?

You are getting good advice here. You have made double sure that the drop links for both sides are dead nuts the same length right? Both sides have the same angle and hit full open throttle at the same time, as well as both resting on the idle stops? There's some pretty schlockey linkages out there, and Joe's dead on with how important the linkage set up is.

I don't know Dells, but I'd try just larger idles, or just larger mains first, but probably not both at the same time.

Where are your mixture screws set at? If you have to set the mixture less than 1 1/2 turns out then I'd try larger main jets, and smaller mains if you've got to go more than 3 1/2 turns out.