Well after much playing and changing I have to say I hate my carbs. I have done every jet size and I can't really get it to run well on anything but 70 idle jets and that is way to rich. With 60s it runs not quite as rich but the hesitation on the initial throttle is huge.

Have played with the adjustments and I think I have it running well but it never performs well. 2056 just built, 44 IDFs, 60 idle jets, 28 vents, 135 mains, F-11 emulsion tubs, 175 air correction jets. Timing at 27 to 30. SVDA Dizzy with electronic ignition. Valves recent set and rechecked. Synced at idle and 1500 rpm.

Runs well at higher rev and pulls strong but I can't get rid of that hesitation. I know there will always be some but at times from a dead stop it almost stalls.

What am I missing?

Gone through all of the Weber tech trouble shooting steps and I can't find anything that says I have something wrong. Is there an adjustment on the accelerator pump? Or do I need to up the accelerator jet?

I will be going back to FI at some point but these carbs should work better than they do. Taking it to Eurohaus tomorrow maybe they will have better luck.

Suggestions?

did you ever try backing one of the throttle stop arm screws off contact?

You say "hesitation on the initial throttle is huge." What does that mean, exactly? Is it always from a "dead stop"? Meaning it falls on its face on the first touch of of the throttle? When you stab the throttle only from low RPM's, or only at high RPM's, or both? Or on a smooth application of the throttle it stumbles at some point as the RPM increases? All of those, or any of them more or less?

Are you using the Weber tech manual? It has (if I remember correctly) some values for the volume of gas from each full squirt of the accelerator pumps. Did you measure that? If not you can get a reasonable idea by watching the stream in each throat as you pump the carbs, but I guess you probably need to know what looks "right" first. to compare.

Oh, and another thing that can cause a low-RPM stumble is low float level and not enough fuel in the bowl.

the carbs in the kit don't have a pump arm adj feature?

I want to say too much Carb for a 2056(does it have a cam?). On my 2056(9550) I am running 40idf with 32 vent, .55 Idles and 1.35 Mains. I am also running big headers and performance muffler. And I am very happy with the performance. Cable Linkage also. Really money well spent on that item!

Good Luck, Mike....

iirc his venturies have been sized to 32s.

Before we go any farther, what distributor are you running?

The Cap'n

Said it's a SVDA and 28 venturis on a 2056, but didn't say what cam.

Well, that's what I get for not reading the original post very well. Is the vacuum hooked up? Correctly? Is the timing set to what it should be with that distributor?

The Cap'n

Cap'n, he said he'd tried timing between 28 and 32, so I'm assuming with a light at full advance. Mike, were you getting timing movement with a light when you varied RPM's? And for curiosity do you know what the timing was at idle?

Ok running through the list!

Stock FI cam.

Floats are set to the recommended spec.

Getting good movement of advance with rpm change. At idle the timing was just slightly advanced for TDC.

Dizzy says 28 to 34 BTDC so I am in that range.

The accelerator pumps seems to be putting out a good stream. Hesitation not present wit 70 idle jets.

Huge hesitation is only at low rpm or dead stop. In 3rd gear at 3000 rpm going to WOT is a slight hesitation that is barely noticeable.

Carbs to big? After consulting with numerous experts the consensus was 40 or 44 did not matter if the vents were sized correctly. Running 28s for more low end performance. Might try 32s but I just don't think that is the issue.

Did I miss anyone?

I cant believe 60 idle jets on 44mm carbs would not run far to rich in the idle circuit.

The throttle plates are still 44mm regardless of the venture sizes.
It is a big carb for that motor.

Camshaft might make it work, but it would need plenty of overlap to speed up the A/F charge enough.

What happens when you run smaller idle jets?

Its an air velocity issue you have to sort out.
Smaller carbs, or more aggressive camshaft with headers and heads to match.

Smaller carbs will make you smile.

While I understand the thought on the butterfly valves, the information I got was that the valves could be 144 but the vent still determined the flow. A 28 vent in a 44 performs exactly the same as a 28 in a 40. Right or wrong that was the opinion of more than one person. I have seen 44s on smaller engines.

Going smaller on the jets to 45 makes it run so poorly that it is clear it is running very lean.

Did you check the linkage. Working on my car today and had similar problems. The passenger carb was opening before the drivers. Basically running on 2 cylinders.

Stock FI camshaft, jets to large, and throttle plates too large with a very slow port speed are clear factual evidence that the opinions you have listened to May not always be right.
40mm is good up to about 2.4 liter, but then you need custom vents to keep up.

How do you know it's running lean? Do you have an Air fuel gauge?
Running 50 idles is pretty typical on a 40 mm carb.
With the larger amount of air moving by the jet, you cannot help but suck in more fuel than a properly tuned 40mm carb, though at a lower speed.

It may be reality that in order to try and compensate for the larger throttle plates, and lower port speed, you may need more fuel to make up for it, but I have a really hard time believing that....

But what do I know.

Did you port match the bottom of the carb to the manifolds?

carbs are all about port velocity, open times (duration) of the camshaft, and the overall sucking power of the engine...it's all a Venturi affect.

You might be able to get it right, or you may need to live with the bogging low speed of the 44 mm carbs on a stock camshaft motor...

Really the issue is the camshaft is really a low duration with little overlap, so the air speed is slowwwwwwww

This works fine with EFI when you can regulate the fuel with an on off switch, but when you regulate the fuel based upon port speed and air flow, you need smaller carbs...or a better air pump....or both.

I'm guessing you balanced the carbs with a uni-sync of some type and that you adjusted the linkage so that they pull the same on each carb ,

when my carbs are out sync (one side getting more fuel there than the other side)
it stumbles and hesatates in the low RPM range & low rpm takeoff , Bill D.

you might want to invest in a weber book , I learned a lot form my dellorto book : )

Yup......stock camshaft.

OK, I missed that, too. I'm a bit off today, sitting down a couple of minutes at a time between moving truckloads of stuff between storage sites for 3 people. Full advance with or without vacuum? The thing I'm getting to is whether there's enough initial advance when the throttle is cracked. Many systems accomplish this with a vacuum retard unit. As in, BAM, you have 10-12 degrees right now.

The Cap'n

Without vacuum. I am going to run through everything again and check to be sure I have not missed anything and let you know.

Lots of good info here Mike.

Rechecking the advance is probably the easiest, but I'm leaning toward a synch problem as well. I'm almost positive this is why I have a similar problem, and I have 40s on a really well built engine. I have Chris' cable linkage, which is a phenomenal product, but because I have earlier style carbs on it without the additional throttle return springs, the passenger side (slave) carb gets pulled open a little at idle/just off idle.

Therefore, I can synch the carbs at idle, but that means at higher rpms they are not synched. So instead, I synch them at higher RPMs, which means they're out of synch at idle and off-idle, which causes it to stumble. At least I'm almost positive that's my problem.

Check your synch at a few different rpms - see if it changes. I do this by using the idle speed screw to hold the master carb at the given throttle position. May or may not be able to do this, depending on the linkage you have.

I would strongly suggest a wide band o2 sensor and an air fuel meter if you want to get your jetting correct.
Otherwise you are guessing.

You can get it right by reading the plugs, which you need to do properly, but it can be done right.

OK so George wins! Rechecked everything and still had the same problem but a little less. Checked the timing with the timing light and it just didn't seem right. So I decided to try setting it by ear. Advanced it until it pinged and slowly brought it back and found the sweet spot. Checked it with the timing light and it was not even close but ran great!

So I am thinking my light is toast. A little hesitation yes but 100% better. I will have my guy check it tomorrow to be sure but it runs too good where it is now to not think it is close and my light is bad.

Thanks for the input it helps a lot.

Too

Unfortunately you'll need to split the case to put a cam in. It straighted mine out and transition through mid range is smooth as silk now.

Thanks for the props Mike, but it was really Rich, the Cap'n, Bill and others who are giving you the right suggestions.

It's possible that it's the timing that's throwing you off, but it's probably a few things compounding here to cause the issues. That initial shot of advance makes a big difference, but so do the others that were mentioned.

In theory, 44s can be choked down with the right venturis, but as Rich mentioned, they really are designed for bigger motors and that's a lot of space underneath the venturi that adds a big variable. Not to mention that the stock FI cam, as many have said, doesn't produce the right vacuum signal at low RPMs to make carbs work the way they should. Obviously, the car will run, but not at it's full potential.

I also agree with the wideband O2 sensor install. Again, I'm a hypocrite as I never got a chance to put one in my car, but at some point I will. It really will take the guesswork out of the jetting at least, and then you'd be able to move back to fine-tuning the other parameters. Sounds like you're on the right track though. Let us know what type of linkage you have, and what the results of the synchrometer are at idle, 2,000 and 3,000 rpms, just out of curiosity.

Yeah, I don't think it's the barrel size, at least not in my experience. Think about it. The job of the carburetor is to atomize fuel, and that happens because of the vacuum created under the venturis. On 40 and 44 IDF's the bowls, jets and passages are identical, so with the same venturi size they create the same vacuum and work, mixing fuel, exactly the same way. Volume/velocities going through the venturis are determined by the engine, the heads, displacement, runner size and cam, not by the throttle plates. Size of throttle plates does make a difference at full throttle, but in every other instance when throttle plates are only partially opened so their overall diameter is mostly irrelevant.

I've used 44's with 28mm venturis on a nearly stock 1.6 engine, used 48 IDF's with home made 30mm venturis on a 1776cc engine, worked great. The hot VW guys all run 48 IDA's on 2 liter engines, standard practice. I've also used 36 DRLA's on stock 2 liter engines. Not exact comparisons, sure, but barrel size (and throttle plate diameter) isn't the determining variable in atomizing fuel, it's venturi size and then sizing everything else accordingly.

I agree with that Painted Guy, everything depends on everything else, so if anything's out of whack it seems everything's off. What you have will work, and it will work well, so you just need to go through it to get everything set up in balance. Unfortunately when you find something that's out that means you need to go through the whole list again, since everything depends on everything else. When you have more experience you can jump over steps, but until then you just have to grind it out. As a hint, look long and hard at the linkage and synchronization, because that usually ends up being the problem when multiple carbs run sour.

my first suspect is still the linkage. as for the 44s with your venturi size. my set sent to utah, came home set up for a 2056, have 32s installed. untrustworthy dels are coming off and i'm going back to the webers.

We have very different opinions and experiences on how this affects the velocity and performance.

Rich

Now recheck your idle jets.

"All" of the recommendations herein are good and "need" to be done in order to tune carbs properly. Carbs being out of sync from one another is a big one.

Webers love advance.

If you plan to stick with them, start planning for that motor rebuild and a new cam. If not, start reading up on D-Jet and collecting parts.

Starting with a valve adjustment, there's a complete process to go through to get them right. Now's the time to do it because you're very familiar with the process. Float bowl levels need to be correct. Linkage and airflow would be next and then finally settling in on jets that rock your world. "Everything" has to be right. Few understand that which is why carbs get a bad rap. Well, that and the fact that they are a pain in the ass!

Give me a buzz if you'd like and I'll run your engine specs on a spreadsheet I've made for jetting. It's pretty much spot on with the exception if the black magic involved in emulsion tubes.

Oohhh! I am guessing that you wouldnt be in the mood for sharing that would you?

What numbers do you need for the spreadsheet?

Number one cause of dual carb issues is linkage, I've built my own linkage (much like CSP centre pull) for for over 20 years. Sync must be done with one arm off then carefully reconnected as to not change anything. Linkage must open equally through the entire rotation. Hex bars (total crap IMHO) often placing unacceptable side thrust loads on the shafts, wearing out bearings/bushings prematurely.

Without a good linkage all adjustments to jets etc., are basiclly like pissing upwind in a hurricane.

O2 meter is now to me a must have, if you are only doing the one car you can just borrow one, but they are so cheap now it is a wise investment. I most often "jet" with a reamer set, but of course that only works when you have to go up in size.

I will agree that linkage is always the first suspect and hex bars are crap. But after taking everything apart and redoing the linkage and sync from step one, I think it is in pretty good shape. Of course that is qualified by the fact that it is still crap linkage.

I may be doing it wrong, but I take all the linkage off both carbs and sync. Then add the linkage back and verifying that the numbers did not change on each side. I also check the sync at 1500 rpm. I am sure it gets out of adjustment as time passes but I feel that this is a part that I can get right or at least very close.

that's why i ask folks to back off one of the throttle stop/idle speed adj screws and use the other one to increase the engine speed to a nice stable idle. not the gas pedal. while the vacuum may read the same at idle with the screws in contact, as you tip the throttle in things can change. this takes about 5 minutes, will tell you if the linkage is set properly when off idle and the progression ports are being uncovered at the same rate.

Synch is still in question here and Kevin's method works. As in the other thread recently posted, look for signs of fuel drips from the accel pumps jets. That is a dead visual giveaway that the carbs aren't synched at idle at least.

Then consult Eric's spreadsheet for jetting, the Weber tech manual, or I also have a (theoretical) spreadsheet that I've been working on for awhile.

Engine size and # of cylinders.

Peak HP the cam is rated at.

Elevation of the city you drive in.

I just happen to know all of Mike's info because I'm a stalker he's a good customer.

Here's what the spreadsheet recommends vs what he has. His is a tad tricky because his elevation can range from 800 down by the river to over 2,000 ft. I used an average of 1000 ft. for this example and frankly it will only reduce sizes by 2%

* Starting with Venturi's - 33 calculated (Purchase 34's) vs 28mm - This is a -20% variance. I really recommend a change here.
* Main Jets - Calculated 155 vs. 135 (you could try 160's and the 175 air corrections) - This is a -15% variance. Change recommended here as well.
* Air Correction Calculated at 171. I'd say you could try 170's but you're probably fine with the 175's. They will help lean out the overall mixture.
* Idle Jets (odd I know) appear to be spot on at 60. The calculate at 60 for sea level and 59 for 1000 ft.

I do not know 44's well enough to recommend an emulsion tube for a stock cam. Check the V-Dub crowd. there should be "tons" of relevant data there. Remember, emulsion tubes follow cams.

Eric - if I still have problems I will try your set up. This will give me a chance to test my next 3D item. Sized to order Venturi's!

We have completed temperature and fuel resistance testing and are moving toward testing them in a car. We should be able to offer a complete set of vents to what ever size is needed for about $40 a set. We are struggling with determining the degree of smoothness needed for the inner finish. The 3D printing leaves small surface lines in the vents that we have gotten conflicting views on the need for eliminating. Might need someone that is testing an engine with carbs on a dyno to see if the vent texture makes that much of a difference.

The weber tech manual says F-7 and F-11 are the consistent all around service tubes so I am not so sure a change is needed there.

Sounds like a cool setup on the venturi's.

I would really recommend making a change in the mains as well. Any extended high speed driving with the combination of those mains and those air corrections could lead to a lean condition and higher temps.

Regarding the E-Tubes... check around. Keep in mind, they may be good all around tubes but, you're not running a carb cam. They can also play (for better or for worse) in your high speed enrichment or, lack thereof.

hence the recommendation of 32mm on my 44s, for a 2056, from ACE.

Eric running lean at highway speeds was exactly what was happening. Going to switch to the 155s (just ordered) or the smallest air correction jet I have until they come in. I would be interested in seeing that spread sheet Eric.

Kevin you are right on the vents! I was trying to bias toward low end performance with the smaller vents but I guess I will concede to the experts!

expert guesser.

Cool. If you go with the 155's you may want to pull your AC jets down now too. 170's might be best with those. If you go 160 main's you could probably stay with what you have. The car would do well at sea level as well.

i'll go pull the jets from the 44s. we'll see how the setup matches the spread sheet. i know for a fact they have 32mm vents in them.

Is this weird or what? Get a spreadsheet involved and it turns into a party? Geeks. Cool, but don't forget you need to get the timing (and valves, linkage, etc) right before you even get to the carbs. The timing's still set by ear? You need to get that right before anything else.

I'm not the one driving a Volvo! (Ooooo that got you and Rich at the same time!)



Keep in mind the cam can have a large effect on your venturi's. I set Mike's peak HP at 5400 RPM. What's yours?

Agree with the timing and the valve adjustment. Very first things to do.

Linkage too. I used two M8 fasteners upside down in the vise to set both drop links perfectly to each other. The other big trick was then hooking them up and adjusting the crossbar linkage so the drop links didn't have to move.

It's all Paul Abbott stuff. Read through the instructions on his site and be prepared to follow them to a T.

The linkage park was one of the biggest changes I noticed. No more erratic idle issues etc. (gee.. why did it idle at 950 at the last stop light and 1200 at this one?)

What? Now I'm offended. Volvos aren't geeky, but carburetor spreadsheets sure are.


5400? Fuel injection cam? I don't know, it's a guess, but I'd bet he's all-in at 4500, and maybe less.

Ummm, I think you're right (not about the Vulvas but...). Not quite that low but, I did some more digging and found the number to be 4900 RPM.

Actual based upon calculations:

Calculated
Venturi's 32
Mains 148
Air Correction 163
Idle 60

Mike, I hope this didn't cause too much pain. Perhaps you can change the order and get some 165 AC's while you're at it.

I would go with:

V = 32
M = 150
AC = 165
I = Keep at 60

Vulvas? VULvas? You're not a doctor, aren't you from Utah or something?

got rid of the last Swedish car a few years back...

Wife got a prius....so not sure about it being better or worse...but she is happy.

Me, all german cars here...just biased I guess.

So no, I no longer drive the vulva....