/6 Weber Carb Questions -> Jets, Who said you can never be too rich? Options

[Carl]

I'm trying to lean out a car that goes through gas like a drunken sailor. To start the process, I want to convert the carbs back to the original factory jetting then address the performance issues if that setting is too lean. Hopefully, there are authorities on carbs out there that know the answers to the following questions:

/6's came with Weber 40IDT3C's, as did the 911T (same engine). The /6 factory manual says the jetting should be:
45 idle jets
105 mains
170 air jets
F1 emulsion tubes

The Pat Braden book on Weber's has the following jetting for 40IDT3C's for the 911T:
50 idles
110 mains
185 airs
F2 emulsion tubes

Which is correct factory jetting for the 914/6?

There are different jetting arrangements for 40IDA3C's. Braden says the IDA's were on the 911L engine. Were they used on other P engines?

There are more references to IDA's in the printed material than IDT's. This doesn't make sense to me if they only came on 911L's because there weren't a lot of them produced vs the 911T's.

What are the differences between the IDA's and IDT's? The external appearance is the same but the jetting is different for engines of the same displacement.

The engine in my car has a 911T crank and case with a 2L 911E pistons, cyls & cams. The 911E was an MFI engine. I've been told there are differences between cams for MFI engines vs carbs. Is this true? If so, how are they different? Should my engine be jetted differently because of it?

and finally, how come a dropped nut will always land in a location that's the most difficult to see, reach, or both? (IMG:style_emoticons/default/idea.gif)

Thanks for the help.

[krk]

This of course is funny. I learned most of my weber stuff from you.

Anyway.

I bet on the /6 factory manual for the /6 factory settings. I'm pretty sure Mr Yellow's IDT carbs were set up to the factory manual -- the silver car is a mixture of things, including IDA's instead of IDT's.

On the diff twixt IDAs and IDTs -- Matt Blast (Eurometrix) said it was nearly irrelevant. To the point that selecting between two sets, you pick the one in the best condition. iirc, the diff is in the idle circuit, and more precisely, something to do with where the transition point is. (this conversation took place 2 years ago -- my "iirc" may not be too "c" -- heh) I have both. I've had them both apart -- the diff was certainly not obvious.

I thought there were way more IDA's out there than IDT's. I could be wrong of course, but it seemed to me they came on several 911 models and the IDT's were only on a couple of years. (I'll dig into what weber materials I have -- prolly the same things you have of course.) IDT's are certainly not often up for sale, where IDA's are fairly common.

Have you had the car on a gas analyzer?

kim.

[Jeffs9146]

my "iirc" may not be too "c" -- heh

What language is this?? (IMG:style_emoticons/default/wacko.gif)

Jeff

[lapuwali]

Bad ignition is the primary cause of bad mileage on a car with the proper jetting, followed by leaky internal circuits in the carb. I'd triple check your ignition system, then start looking for ways fuel is leaking internally in the carb. I've seen cases on IDFs where fuel mileage is cut it half by a dribbling accelerator pump circuit, yet the car runs fine otherwise.

[Carl]

Jeff: iirc = if I recall correctly

Thanks, Kim. I ran through my entire inventory of Weber knowledge that day we tried to tune yours. Not too successfully, iirc (there it is again, Jeff). You've since gone on to greater heights in Weberdom so now I can only hope to pick up some fragments from you.

Some questions related to all this:
A while ago I got recommendations for Webers on an E engine and that's the way my carbs were set. 55 idles, 125 mains, 180 airs and F1 tubes. This is just way too rich. Gas mileage sucks, the plugs are quite dark and the exhaust smells gassy. I don't know why this setup would be desirable.

I've not had the car on an analyzer for fear of pegging the meter and thought I'd fall back to original specs and experiment.

Thus the questions. Where to start?

[Carl]

Bad ignition is the primary cause of bad mileage on a car with the proper jetting

That is on the agenda. There may be a problem with sticky advance weights in the dizzy but I need a timing light to check. Will do that soon. The dizzy has been changed to pointless so, aside from timing and the advance, there should be few distributor issues.

[Brad Roberts]

I need to setup a dyno day next week to tune in a 3.0 9146. You are more than welcome to schedule with me. Typically it is 85/95 an hour. I can get 3-4 pulls in a 1 hour time frame on each car. I baseline it then make adjustments. I *think* it is another 25/35$ to hook up their 4 gas analyzer (which is what I have to do to get anywhere) I will be bringing over 50 different jets with me to dial in the 3.0. You make the call and let me know what day is good for you. The plan is start late in the afternoon around 2:30 PM. The dyno place I want to schedule with is in Santa Clara off of El Camino and De la Cruz. If I cant get time there I will go to a place down closer to you and Kim off of Almaden expressway/87.


B

[ArtechnikA]

one of these days i'll pull the carbs from my car and open them up to see what i put in there back in the day. it was The Hot Setup - jets, emulsions, extended ('906') aux venturiis, bigger venturiis, the lot. the car's still ot the 140 main jets i used on the track with the open (megaphone) exhaust but main jets is all i ever changed for the track.

i don't think i can do that this weekend, tho, but i will try. i'll post the results here when i do.


BTW - stock /6 carbs are 40 IDTP13C...

[Carl]

I need to setup a dyno day next week to tune in a 3.0 9146. You are more than welcome to schedule with me. Typically it is 85/95 an hour. I can get 3-4 pulls in a 1 hour time frame on each car. I baseline it then make adjustments. I *think* it is another 25/35$ to hook up their 4 gas analyzer (which is what I have to do to get anywhere) I will be bringing over 50 different jets with me to dial in the 3.0. You make the call and let me know what day is good for you. The plan is start late in the afternoon around 2:30 PM. The dyno place I want to schedule with is in Santa Clara off of El Camino and De la Cruz. If I cant get time there I will go to a place down closer to you and Kim off of Almaden expressway/87.


B

That would be GREAT! Now Kim's going to have to clean that tank this weekend.

Tues and Thurs are out for me but Mon, Wed & Fri would be OK.

[Brad Roberts]

The more cars I can get the better off we are. I think JasonS would like to dyno "ugly" also. The 4 gas setup is the hot ticket for tuning. Mixing it in on a chassis dyno pull will show us the whole range from 2000RPM to redline. Since you and Kim know how to change the jets this whole process will go quickly.

I'll contact my customer (Vito is his name) and let him know I would like to shoot for Mon/Wed/Fri.


B

[krk]

my "iirc" may not be too "c" -- heh

What language is this?? (IMG:style_emoticons/default/wacko.gif)

Jeff

heh -- Carl nailed it. My "if I recall correctly" may not be too "correct".

kim.

[Carl]

Tuesday would be a problem. 30 year anniv. with the bride means it's time to park the car and spend an evening with the fam.

[krk]

I need to setup a dyno day next week to tune in a 3.0 9146. You are more than welcome to schedule with me. Typically it is 85/95 an hour. I can get 3-4 pulls in a 1 hour time frame on each car. I baseline it then make adjustments. I *think* it is another 25/35$ to hook up their 4 gas analyzer (which is what I have to do to get anywhere) I will be bringing over 50 different jets with me to dial in the 3.0. You make the call and let me know what day is good for you. The plan is start late in the afternoon around 2:30 PM. The dyno place I want to schedule with is in Santa Clara off of El Camino and De la Cruz. If I cant get time there I will go to a place down closer to you and Kim off of Almaden expressway/87.


B

That would be GREAT! Now Kim's going to have to clean that tank this weekend.

Tues and Thurs are out for me but Mon, Wed & Fri would be OK.

Carl, this is *the* ticket. A dyno and a gas analyser.

I'm in -- can't come Thurs. Fri is actually best. (Thurs is a huge day for me and stealing time in front of it is possible but.... you know)

kim.

[Brad Roberts]

Friday will probably be best. I have NO idea why I typed TUES in the post above (I changed it..LOL)

B

[krk]

Jeff: iirc = if I recall correctly

Thanks, Kim. I ran through my entire inventory of Weber knowledge that day we tried to tune yours. Not too successfully, iirc (there it is again, Jeff). You've since gone on to greater heights in Weberdom so now I can only hope to pick up some fragments from you.

Some questions related to all this:
A while ago I got recommendations for Webers on an E engine and that's the way my carbs were set. 55 idles, 125 mains, 180 airs and F1 tubes. This is just way too rich. Gas mileage sucks, the plugs are quite dark and the exhaust smells gassy. I don't know why this setup would be desirable.

I've not had the car on an analyzer for fear of pegging the meter and thought I'd fall back to original specs and experiment.

Thus the questions. Where to start?

Now you're pulling my leg!

The first set of carbs were so leaky around the shafts that we were doomed before we started.

But you do have a good question -- what should you set for the starting point. (do the dizzy check before of course)

Idles/Mains are certainly easy to swap in and out. We just need a few sizes to play with. We should just gather our inventory of the stuff we have together and figure out what to bring and what you would like to try.

F-tubes are of course harder and probably not practical -- it'd be easier to swap carbs on and off -- hm.. did you mention the venturi sizes? Those are also not so easy to "swap".....

kim.

[campbellcj]

Definitely double check the main venturis/chokes as that makes a huge difference in how much top-end the car makes, and where it is made. IIRC the stock 914-6/2.0T had 27mm venturis. I have 32mm's in my 2.2"S/T" and full race motors usually run 34's or bigger. The wrong choice can just kill your A/F and drivability.

[Carl]

Definitely double check the main venturis/chokes as that makes a huge difference in how much top-end the car makes, and where it is made. IIRC the stock 914-6/2.0T had 27mm venturis. I have 32mm's in my 2.2"S/T" and full race motors usually run 34's or bigger. The wrong choice can just kill your A/F and drivability.

I'm glad you made that point, Chris. The /6 manual says 27mm venturis and the Braden book says IDA's are spec'd at 30. I've had 30's in mine but have had a giant flat spot from 1500 - 3000 rpm. I changed them back to 27's but still had the dead spot. It seems to be better with the leaner jets but I've not driven it much with all the changes.

I think you're right, Kim. We can change idles and mains, and, with a little work, the airs and e-tubes but venturis will take too much time.

C

[Red-Beard]

My 914/6 turned out to have 32's and the idle never seemed right. I also think I have problems with the bushings leaking.

So, as I have cylinder #4 fixed... (nuther story), I'm going to have the Carbs rebuilt by an expert...

As for tuning, I like the Tomlinson weber manual. the reccomended parts, which I purchased, I think were very baseline and are actually, undersized for what the 2.7 RS spec engine will do. Even after moving to 34's, the engine is sucking wind at 6500 RPM. I think I need to move to 36mm chokes, so I can possibly achieve the 7300 RPM this engine is supposed to be able to do. And then start screwing with the rest of the adjustments.

Get the Tomlinson book...

[J P Stein]

I could ramble on for pages about Webers, but I'll try to keep it short.

General stuff.

The gas you are buying today is not the gas that the cars (and carbs) were designed to run on.

If you're not fouling plugs and the engine runs good, you're not too rich. Rich is mucho better than lean......at best, lean will cause flat spots in the transition rpm range......holes in pistons are another option.

These carbs are 20-30 years old. Stuff wears out and a "rebuild kit" won't fix that. ALL the rubber shit goes to hell. The rebuild kits will fix that.

There are lots of screws & nuts that do things. Learn what they do and and the proper sequence of doing them......if you know someone that has this info, bribe him with beer & women so's he'll teach you. There are also a few simple tools to assist you in tuning them.

IDA & IDT have a different shape to the mixture screws....they are not interchangable....tho they will screw into the holes. The IDAs have a straight tapered needle, the IDF has a radius taper. I assume their seats have coresponding tapers, but am not sure of that.

MSD systems are a Godsend for Weber carb guys....it took me a year of dickin' around to discover that. I haven't touched the adjustments for about 2 years.

I gotta admit, gas milage is the least of my worries.

I read the books. They give you the basics but not all of them.

I'm done. (IMG:style_emoticons/default/biggrin.gif)