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Posted by: Mblizzard Oct 30 2013, 12:13 PM

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?

Posted by: rhodyguy Oct 30 2013, 12:17 PM

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

Posted by: DBCooper Oct 30 2013, 12:42 PM

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.

Posted by: rhodyguy Oct 30 2013, 12:54 PM

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

Posted by: 7275914911 Oct 30 2013, 01:00 PM

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....

Posted by: rhodyguy Oct 30 2013, 01:03 PM

iirc his venturies have been sized to 32s.

Posted by: Cap'n Krusty Oct 30 2013, 01:16 PM

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

The Cap'n

Posted by: DBCooper Oct 30 2013, 01:30 PM

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

Posted by: Cap'n Krusty Oct 30 2013, 01:59 PM

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

Posted by: DBCooper Oct 30 2013, 02:27 PM

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?

Posted by: Mblizzard Oct 30 2013, 03:28 PM

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?

Posted by: r_towle Oct 30 2013, 03:29 PM

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.

Posted by: Mblizzard Oct 30 2013, 03:36 PM

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.

Posted by: Jetsetsurfshop Oct 30 2013, 05:11 PM

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.

Posted by: r_towle Oct 30 2013, 05:14 PM

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.

Posted by: r_towle Oct 30 2013, 05:25 PM

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.

Posted by: WLD419 Oct 30 2013, 05:41 PM

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 : )

Posted by: 914_teener Oct 30 2013, 05:43 PM

Yup......stock camshaft.

Posted by: Cap'n Krusty Oct 30 2013, 05:56 PM

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

Posted by: Mblizzard Oct 30 2013, 06:26 PM

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

Posted by: ThePaintedMan Oct 30 2013, 06:44 PM

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.

Posted by: r_towle Oct 30 2013, 07:02 PM

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.

Posted by: Jetsetsurfshop Oct 30 2013, 07:13 PM

Posted by: Mblizzard Oct 30 2013, 07:39 PM

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.

Posted by: struckn Oct 30 2013, 07:56 PM

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.

Posted by: ThePaintedMan Oct 31 2013, 07:29 AM

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.

Posted by: DBCooper Oct 31 2013, 11:48 AM

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.

Posted by: rhodyguy Oct 31 2013, 11:56 AM

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.

Posted by: r_towle Oct 31 2013, 12:02 PM

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

Rich

Posted by: Eric_Shea Nov 1 2013, 07:33 AM

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.

Posted by: stugray Nov 1 2013, 08:24 AM

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

What numbers do you need for the spreadsheet?

Posted by: Mark Henry Nov 1 2013, 08:35 AM

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.

Posted by: Mblizzard Nov 1 2013, 08:44 AM

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.

Posted by: rhodyguy Nov 1 2013, 08:47 AM

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.

Posted by: ThePaintedMan Nov 1 2013, 09:36 AM

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.

Posted by: Eric_Shea Nov 1 2013, 09:59 AM

Engine size and # of cylinders.

Peak HP the cam is rated at.

Elevation of the city you drive in.

Posted by: Eric_Shea Nov 1 2013, 10:18 AM

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.

Posted by: Mblizzard Nov 1 2013, 11:02 AM

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.

Posted by: Eric_Shea Nov 1 2013, 11:15 AM

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.

Posted by: rhodyguy Nov 1 2013, 11:25 AM

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

Posted by: Mblizzard Nov 1 2013, 11:47 AM

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!

Posted by: rhodyguy Nov 1 2013, 12:02 PM

expert guesser.

Posted by: Eric_Shea Nov 1 2013, 12:16 PM

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.

Posted by: rhodyguy Nov 1 2013, 12:21 PM

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.

Posted by: DBCooper Nov 1 2013, 12:53 PM

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.

Posted by: Eric_Shea Nov 1 2013, 01:06 PM

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?)

Posted by: DBCooper Nov 1 2013, 01:13 PM

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.

Posted by: Eric_Shea Nov 1 2013, 01:35 PM

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

Posted by: DBCooper Nov 1 2013, 02:03 PM

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

Posted by: r_towle Nov 1 2013, 02:29 PM

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....

Posted by: Eric_Shea Nov 1 2013, 03:08 PM

Damn spell checker on my phone. Sorry...

Posted by: Mblizzard Nov 3 2013, 04:48 PM

Ok so I switched to the new 32mm 3d printed vents that seem to work well but I can't keep the carbs synced. So I have to punt the hex bar and go for another linkage. Suggestions that won't break the bank?

Posted by: ThePaintedMan Nov 3 2013, 11:11 PM

I personally like the Tangering Racing cable setup. Chris knows his stuff, and it's really not much more expensive than most other options. If you have the earlier carbs though without the helper return springs, you might have some issues like I do with the slave carb closing all the way. An easy fix though with a homemade bracket and spring. It's also the cleanest solution and really takes a bunch of crap out of the engine bay. Piece of cake to tune and synch too.


However, the CSP bellcrank setup is well known as a good alternative too - McMark I believe did a big group buy on those awhile back?

Glad you're tracking things down Mike! It'll get there! Can't wait to see pics of the printed venturis!

Posted by: DBCooper Nov 4 2013, 06:48 AM

Wait a minute, first things first. Your last comments were that you'd done it by ear, so have you found a way to set the timing yet? If not then you need to, before you do anything else. If the timing's not right then anything else you do is irrelevant.

Just an observation, there are better linkages, no question, but a lot of people have used hexbar linkages successfully for a long time. Google it and you'll find lots of hints and procedures that people have come up with to get them configured (most important) and keep them adjusted. You can make the hexbar work well. I don't want to suggest that it's not some work, or that you shouldn't spend the money if that's what you want, but I think you still have things left to do to get the thing correctly in tune first.

Posted by: Mblizzard Nov 4 2013, 07:33 AM

I did get the timing correct. I have everything else set according to instructions. But when I have both carbs balanced at idle, at 1500 rpm on is at 7 the other is at 10. So I work on the linkage of the one lagging for a while and get it to 7 at 1500. Secure everything. Runs great sitting. Go for a drive and it gets out of balance above idle. Spent 3 hours doing this dance and never could may it work. Granted it may be operator error but I think there is something wrong with the linkage. I could try replacing parts but if it takes that long to figure it out and it needs new parts when it is only a few months old then I lean toward replacing it.

But I am going to try again as you suggested before I spend the money.

Posted by: rhodyguy Nov 4 2013, 07:46 AM

pass side idle speed adj screw off the stop?

Posted by: 7275914911 Nov 4 2013, 07:58 AM

The CSP Bellcrank is very easy to adjust/stay adjusted and very smooth response but you will still have the hunting idle trouble that Shea mentioned. It is very well built.
But I agree with George that Cable is the way to go IF you are going to spend the money. I have Chris's early setup but did have to have work done on my early webers to make them work.
I have ran both but haven't had a Hex Bar setup but as a few state it wouldn't still be around if it didn't work?

Again, Good Luck!

Posted by: DBCooper Nov 4 2013, 08:23 AM

If the adjustment is changing just because you're driving it then something's not staying where you put it. So if something's moving, what is it? And why? First do you still have some cable slack at full throttle? By that I mean when you floor the pedal are you pulling at the linkage past its stop? On either carb? If you are and you floor it on your test drive you're stretching and "unadjusting" the linkage. Second if something's moving you should be able to find it. Take the linkage drop arms and twist them (softly!) back and forth in different directions. Feel anything moving? Do the same (softly!) with the cable arm and each drop arm, back and forth, anything move? And is the length of your hexbar adjustable? How do the ends sit in the carb mounts? Can you feel any binding? Some have bushings, some bearings, push the bar back and forth and in and out near the carb pivots, feel any movement?

By the way, before the protests start I'm NOT endorsing hex bar linkage, by any means. It has two problems, first the initial setup and second maintaining the setup. The initial setup is logical, you just need to go through it and there are DOZENS of instruction sets on the web, just google. The second, staying in adjustment, is problematic because hex bars have so many different components that are long levers with angles joined with fasteners, so even slight movement anywhere will put them out. That means their adjustment doesn't last as long as it should, but that's typically months or more between adjustments, not minutes. You can do this, tens of thousands of other have, just work your way through it.

EDIT: One other thing, is your hex bar steel or aluminum? If it's aluminum then you can still adjust it, but start saving for something better. And it is a real hex bar, right, not tubular? There were some really cheap tubular bar linkages sold, but I doubt there are any left that haven't been thrown into a lake by now.

Posted by: rhodyguy Nov 4 2013, 08:49 AM

and if the xbar is one of the spring loaded (the outboard ends) ones you're fighting that. in my experience, the offset nature of the intakes and if the cable isn't square to the bar attach point you're pulling the the bar sideways right from the gitgo. DID YOU EVER BACK THE SCREW OFF THE STOP? sorry i raised my voice.

Posted by: Mblizzard Nov 4 2013, 09:21 AM

Of course mine is one with the springs at the end! It is steel.

I checked at one point to be sure that the cable was not still pulling at WOT but I have not checked recently.

No sure what you mean Kevin by the screw off the stop? Are you talking about the idle speed adjustment?

I just think there are too many moving parts at the wrong angles. For example. Where the adjustable threaded rod goes from the cross bar attaches to the carb throttle linkage, the diameter of the hole in the carb linkage is bigger than the bolt on the end of the rod. Not a big movement but certainly it can change up and down even with the nut tight.

And I have never under stood how the threaded rod with psi it points on both ends is ever suppose to stay exactly the same as the other linkage when they are independent of each other.

Posted by: rhodyguy Nov 4 2013, 09:47 AM

yes, the idle speed adj screw on the pass side. take the potential bind, what could be artificial equal flow at idle out. the dr side isas then controls both carbs. after doing the vent swap you prob want to go thru the pre run setup procedure detailed in the cb book. you should be pretty well versed in it.

Posted by: Eric_Shea Nov 4 2013, 10:02 AM

Have a friend watch the throttle plates as you press the accelerator. Then move the throttle stop under your pedal to accommodate.

The linkage is mechanical. If there are no worn parts it will work if adjusted properly. If adjusted once and then it becomes "un-adjusted" something is at play.

* Adjust the valves
* Set the timing properly (error on the advanced side)
* Fuel pressure must be at 3.5 PSI
* Carbs should be sync'd and tuned with the linkage "off"
* Follow procedures for the idle screw. Not having the engine timed properly can lead to an exaggerated idle setting just to get it to idle and carbs that wander into the progression circuit.
* Drop links should be set at equal lengths. (two 8mm bolts in a vise)
* Linkage mounts should be adjusted to accommodate the equal length length drop links.
* Cable should be adjusted to stop when the plates are at WOT.

Some of this may only apply to the IDA3C type carbs (linkage mount adjustment) but, what is hopefully emerging is a pattern of "everything" has to be right in order to tune a carb properly.

Posted by: DBCooper Nov 4 2013, 10:36 AM

And just in case you missed it:

Go through it all again, the CB book if you have it and Eric's list. NO KIDDING.

Posted by: 72hardtop Nov 11 2013, 01:18 PM

No ones made mention of this but I've seen it quite often...check to make sure you installed the aux. vents properly.

Posted by: Mblizzard Nov 11 2013, 01:22 PM

Chris pointed out in another thread that they were NOT installed incorrectly. Funny thing is that I have photos with them installed that way right out of the box.

I installed Chris's throttle linkage to address the issue once and for all so I will let everyone know the result soon.

Posted by: Mblizzard Nov 16 2013, 11:49 AM

Well I finished the install of Chris Foley's/ Tangerine Racing throttle linkage. I have a completely different car! Runs strong, no hesitation, 2 minutes to sync, and pretty easy to install. I have not driven it very far and I changed a few things in the carb based on Eric's suggestions, but it is clear that this is the best way to run dual carbs.

The time I wasted messing with that hex bar certainly justifies the cost of this package.

Thanks for all the input.