Weber tuning frustration

I would suspect the linkage. What does yours look like?

quote:

Originally posted by PanteraDoug:
I would suspect the linkage. What does yours look like?

The carbs are not hooked together yet, so far each carb is set up individually, independent of the others. they are pulling the same CFM. the cool bank on the right does not appear to respond to adjustments as the hot left bank.

Did you use the sync tool?

Hi Doug – how do those sync tools work?

Are they just basically a manometer that you adjust for the same airflow, or pressure at all of the carburetors?

Thanks in advance for the description.

The flow at idle on these carbs is so delicate, that you balance that flow with this device.

You sit it on top of the velocity stack, then equalize the calibration with them with the ball that floats in the glass tube.

Weber carbs have soft brass throttle shafts. Ham handed throttle construction can very often twist them.

Once they are twisted you will have un-equal flows from one throttle plate to another in the same carb. That makes it impossible to sync the carbs.

This sync device will help you determine that.



Weber linkage has to be VERY light basically relying on the throttle return springs built into the carbs themselves.

Many linkage set ups that I have seen require too many additional return springs to zero the linkage.

The return springs go on the center linkage pivot, not the carb throttle levers.

The Pantera linkage is unique to the car itself. Generally speaking you HAVE to use the center tower to make it work.



The side loading linkage that Inglese has are really for the Mustang. It is not going to work properly in a Pantera and likely will result in you twisting up the carb throttle shafts.

Believe or disbelieve but I'm the one who did the initial jetting setup on the Clevelands for Jim, with his parts, but it was me. Circa 1978.

This was all proprietary information then and no one was sharing jetting info on the carbs for this set up. You had to figure it out for yourself.



At the time, the set up was in my 68GT350 and had to use his design for the side loading linkage. Carbs had to be parallel rather then opposed as in the Pantera manifold design.

When it, mine, was transposed to my Pantera, all it would do is jamb open and not return to zero. That linkage design became useless.



The original Pantera Weber design was done by Holman-Moody for Ford and GIVEN to Detomaso.
The center tower is there for a reason. Yon NEED to use it.

Change the throttle design at your own peril. It's your car and you of course can do anything that you want to but it isn't easy being completely on your own. Because of the location of the engine the access to the set up is difficult. You don't want to endlessly be messing with it.



All I can say is that it was my observation that Jim couldn't make it work and went to the side loading.

The only Pantera that I ever personally seen him set up was Andy Carr's back in 1980 or so. He was having problems with the linkage on that car.

I know because I was riding as a passenger in it when he locked up the throttle and spun it on an entrance ramp to RT95 in CT. It was right after a snow storm and there were snow banks along the roadside.

There was no rear deck lid on the car with open stacks, no screens. No Weber cam. Carbs fuming atomized fuel like a volcano.

First time I ever heard the valves float on a Cleveland. That was fun. Yikes!

Glad it wasn't my car.


You have three choices now. 1) work it out yourself 2) pay someone to fix this for you 3) take my info for free.

I'm not an unlicensed MD. I don't right prescriptions. I share my experiences with others. This is not "theory". You can take it for what it's worth or ignore it completely.

"Frankly Scarlett, I don't give a dam", so to speak?


I did my center linkage like this. The benefit is that it doesn't pull on the carbs themselves, just is the secondary return spring tracks require.

The throttle pedal is very light. Feels more like an electronic throttle.

I hope it helps.

To balance idle depressions on Weber, the most practical tool is a board with mercury columns. It makes it possible to see all the barrels together for a 4 cylinders engine or at least a complete bench for an 8 cylinders which is very practical because when we tune a barrel it affects all the others because the speed of the engine varies

I made one 40 years ago and I still use it.

Thank you for the additional advice. I did use a sync tool and the CFM reads nearly identical. but I will dial it in better. However the difference in the two sides appears larger. Maybe that small difference is the key. I can feel the header tubes and they are not identical temperature as they heat up after starting. More fussing will follow. I like the challenge, but will pull in a third party if all else fails.

thanks for all the input, it's half the fun of trying to go it alone. I am getting closer, the heat of the header tubes gives me some fuel delivery information, however now I'm still running too rich which runs contrary to the basic tuning settings I found in various locations. Unscrewing the needle valves by 1+1/2 to 2 turns as a base setting appears way out.

Thanks for the report. Keep us posted.

The color of the plugss is a much better indication than the feeling of the heat released by the headers and to do really good work, nothing is better than a broadband lambda probe.

Hi Tom, I've seen the 'hot/cold' issue before, although with individual cylinders, not the entire bank. At least on my setup, minor adjustments to the idle mixture screw at the base of the carb can bring a cylinder with 'cold' exhaust to idle properly. (There are of course eight - one per cyl - and none end up in the exact same position; I must dial-in each cyl individually to give maximum revs at idle at a given throttle setting. As they get dialed in, engine idle rises, so the throttle setting for all carbs must be reduced collectively to a normal idle speed.

I use a homemade extender to reach the screws (pic 2) - small nail in an aluminum tube - on my obscured LH carbs. RH is easy w/ this side-pull 'reversed' setup. On your car clearly no adjustment screws are easy to reach

If your carbs are not linked together that complicates the above idle adjustment...I guess you could throttle an individual carb back down once 'best' idle mixture settings are found, but then the sync setting is messed up again. I would connect the linkage, sync all carbs (ideally with a setup like Rene's), THEN adjust idle mixture.

The only other thing that came to mind was fuel pressure. I know everyone says you need c. 3 psi for Webers but I have accidently run 8-10 at times due to a hair-trigger Filter King pressure limiter, and the engine doesn't seem to care much(!). So maybe it's not a HUGE deal but surely best to run c. 3-3.5 psi.

Please let me know if you know of a Weber expert in our area, I'd like to have my system evaluated at some point, once everything else on the car is good to go....

Tuning tool:

Sorry just now saw your comments re. mixture. Agree 1.5 - 2 turns sounds like a lot - - THINKING mine are generally around 1 turn out. Whatever the case the difference of 1/4 turn away from exact 'best' idle setting seems to be enough to shut down idle on that cyl.

quote:

Originally posted by nate:
Tuning tool:

I like it. Nice thinking.

To synchronize depressions the procedure is as follows:
- close ALL air-screws completely and adjust the linkage so that all carburetors are just completely closed.
- screw the general idle-screw so that the engine can just idle
- Carburetor per carburetor, open the air-screw of the barrel which has the greatest depression until the two depressions are the same.
- Adjust the linkage between the two carburetors of each bank of cylinders to obtain the same depression on the four barrels. It may be necessary to retouch the air-screws but always acting on the same screw
- adjust the linkage between the two banks of cylinders. Again it may be necessary to retouch the linkage between the two carburetors of a bank and possibly air-screws
- after each adjustment, give a short throttle and let the engine come back to idle then adjust the speed of the engine with the idle-screw


At the end, each of the four carburetors must have one of its two air-screws fully closed.

Then adjust the richness of each barrel with the gas-screw to obtain the highest engine speed but on an 8 cylinders, it is necessary to have a very fine ear or a lot of experiment, from where the utility of lambda probes.

I installed lambda probe nuts on the exhaust of each cylinder of my Westfield (2 liters Opel 4 cylinders engine with two Weber 45 DCOE) and I confirm that 1/8 turns on the gas-screw makes the lambda vary significantly. It's a very fine tunning.

I do not know in the US but in France there are almost no mechanics who still able to do that, the good repairers of motorcycles, when they agree to work on a car, know how to do.

It is already long to properly synchronize a four-cylinders, I do not imagine what it is for an 8. Good courage.

quote:

Originally posted by René #4406:
To synchronize depressions the procedure is as follows:
- close ALL air-screws completely and adjust the linkage so that all carburetors are just completely closed.
- screw the general idle-screw so that the engine can just idle
- Carburetor per carburetor, open the air-screw of the barrel which has the greatest depression until the two depressions are the same.
- Adjust the linkage between the two carburetors of each bank of cylinders to obtain the same depression on the four barrels. It may be necessary to retouch the air-screws but always acting on the same screw
- adjust the linkage between the two banks of cylinders. Again it may be necessary to retouch the linkage between the two carburetors of a bank and possibly air-screws
- after each adjustment, give a short throttle and let the engine come back to idle then adjust the speed of the engine with the idle-screw


At the end, each of the four carburetors must have one of its two air-screws fully closed.

Then adjust the richness of each barrel with the gas-screw to obtain the highest engine speed but on an 8 cylinders, it is necessary to have a very fine ear or a lot of experiment, from where the utility of lambda probes.

I do not know in the US but in France there are almost no mechanics who still able to do that, the good repairers of motorcycles, when they agree to work on a car, know how to do.

It is already long to properly synchronize a four-cylinders, I do not imagine what it is for an 8. Good courage.

On 48IDA's it is unusual to be able to get all 8 cylinders to idle equally.

You can't even get the same carbs equal. Once cylinder usually will be higher then the other.

You need to experiment to see if the dominant cylinder on each carb is the higher or the lower setting,

For me it normally works out to be no more then one gradation mark on the sync tool.

Then it is balancing back and forth until you have them close.


The plugs should be a dark brown. Some describe that as a rust color. They should not be black.

On my engine, the idle set screw vary slightly from cylinder to cylinder but are in the 5/8 to 3/4 turn out.


It's very common to foul a set of plugs up while doing this. In fact, maybe two.

I have found that with the ida's, the ignition likes a slightly hotter plug but also remember that I am using different cylinder heads. Aluminum, not iron.

They have different requirements.


Also, in case you have not already discovered it, the engine likes an idle jetting of .60f/.85a.

Depending on the camshaft configuration, you may also be able to lean that out to a .90 idle holder.

For a long time, the only idle jetting available was a .70f/1.20air (idle jet holder). The seemingly sudden availability of small air jet holders made leaning down the idle possible along with adding a third transfer hole to reduce the transfer flat spot.


Forget about trying to get a lean idle with the carbs. About 12.5-12.0:1 at idle is as lean as you can go without the carbs popping through the exhausts at idle.


You HAVE to install the linkage before you do any of this and you are going to need to work back and forth from the idle screws to the linkage to zero it.

This isn't easy AND if your linkage does not have the right geometry, once you drive the car, the idle will be all wrong again.


The set up of Nate's car is using Inglese's re-orientation plates. That was Jim's solution to removing the over/under linkage working off of the center turnbuckle and tower.

It worked on my '68GT350, but not on my Pantera. My Pantera I could only make work with the center tower.

The ONLY reason that you use those reversing plates is to simplify the linkage.



When you reverse the one bank of carbs to put them all in parallel throttle positions, you loose power in the engine because you loose line of sight from the throttle to the intake valve.

How much I can't say scientifically because I never dynoed all of these possible combinations but I can feel the difference as a driver.

I would SUSPECT something like 25hp loss or the difference of running a Holley carb with a factory air cleaner or an open carb.



Mine idle now at 775rpm, with 15 degrees initial advance and a non Weber camshaft with 245 degrees duration @ .050 and 72 degrees of overlap.

You will also see the idle vacuum change as you make these changes and adjustments. I can only get about 11.5-12 inches at this idle speed. More if I idle up. Probably 14 at about 1,000 rpm?

I don't worry about that any more since I put a vacuum pump in the car and that gives like 18-20 inches for the vacuum accessories.



So it is possible to get them "civil" (depending on your definition), it just takes a lot of patience and as I remember about 2 weeks of work to get it right.

I remember Inglese making the final comment to me on the Shelby, "if you think they are right now (or you are happy with them) LEAVE THEM ALONE!"



I don't see how you can save all of the settings when you take them off of the car. You are going to have to go through this every time you reinstall them. Settings are so sensitive that just one bump in disassembly changes things.

Others I am sure have different experiences? These are just some of mine and solely intended to save you some of the pain. However, if you are into pain and love the challenge, challenge away! Have fun.



Oh...I have found that the P-E iginition is a gift from "Heaven" with the Webers. If will fire and clean up a completely fouled plug. NO other system will do that. Not the Ford or the MSD.

In fact, it was the MSD that kept failing and wouldn't start the car after sessions of "Weber tuning". That just compounded the issues and made it near impossible to determine where the problem was.

There is a vacuum outlet on each body of each carburetor.

Yes, it's better with 8 columns than with 4 but we can do the two benches one by one and balance them after.

Anyway Panteradoug is absolutely right, it is very difficult to get exactly the same depression everywhere, especially as it always moves a little bit and I'm happy when I arrive at a difference of less than 5mm of mercury on a 4 cylinders, then on a 8 ...................

quote:

Originally posted by Marlin Jack:
...One more question, Please. Trying to stay on topic.

You say 8 vacuum ports.
Are ALL 8 Ports Connected Together at a 'union' of One (1), permanently, as the Engine is being Run?
and would this 'Help' to 'Balance Out' the Carbs?

Thanks.

MJ

No, when the motor runs the 8 ports are closed.