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

[terrymason]

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?

[Grelber]

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

[BxtrBill]

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

[terrymason]

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?

[PeeGreen 914]

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.

[DBCooper]

The problem is that dellortos suck. Sorry if you love them, but I have thrown three pairs in the can.

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.

[type11969]

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

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?

[terrymason]

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.

[904svo]

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

[BxtrBill]

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)

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.

[type11969]

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

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.

[BxtrBill]

[/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.

[terrymason]

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)

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?

....

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.

- 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.

[terrymason]

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.

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.

[terrymason]

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

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?

[type11969]

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!

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?

[type11969]

.1, .2, .3, .4

[IronHillRestorations]

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.

[rhodyguy]

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

[type11969]

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.

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