Weber 40ida: What needed to change use

[911 tweaks]

Hey all, I was wondering if the ones whom have traveled down the road of rebuilding & using weber carbs could give me some tips on what I have ahead of me.

I wish to plan what tools, parts & ref material I will need to rebuild a pair of weber 40ida3c carbs that were previously used on either a 2.0 or a 2.2 size engine.

This is what I have gleamed from the archives so far:
Tools:
1. qty. 2 synchrometers (thx Ronin sor the tip) (pelican p/n pel-tol-stesk)
2. Float gauge (Pelican p/n pel-pmo-004)
3. jet gauge (which tool: #A tool range of 0.45mm-1.5mm OR #B tool1.5mm-3.0mm?)

Reference materials:
1. Wayne's 101 Project book; project 28 to rebuild & 29 for tuning
2. BA book pg 153-155
3. Weber tech manual by Bob Tomlinson
4. Weber Tech manual by Pat Braden
5. Weber factory tuning manual

Parts needed:
1. what rebuild kit as pelican is out of stock ?
2. engine is an 82' stk 3.0 w/ stk cams... what size carb parts do I need & where get ?
3. If I was to use 964 cams, would different carb jetting, ect. be needed?

Thanks in advance to all that can help me out!
Bob

[RoninLB]

although not answering any questions it's good to keep the idea that the efficency of carbs is directly related to the act of gas atomization. The smaller and finer the mist the more efficent combustion will be. Carbs are also a comprise in usage. A carb tuned for street use will be different than a carb used for WOT and near WOT. Tuning fuel flow for acceleration is a simple example. Too much gas:air crashes your EGTs. Not only do the droplets become big but the excess gas cools combustion tempertures. Heat is power.

I would also seek out what other pelicanhead carbed 3.0 guys do.




Still about Weber jetting (heres mine and gotta ask)

from above T Bird posting..

Venturi Size -- Weber formula to calculate the size of the venturi.
(1) - Divide the volume of one cylinder in cc's by 1000.
(2)- Divide the rpm where peak power is made by 1000.
(3)- multiply the number derived in (1) by the number derived in (2).
(4)-Take the square root of the number derived in (3).
(5)- Multiply the number derived in (4) by 20.

The numbers work out like this for a 2.4T.
(1) 2400cc / 6 = 400; 400 / 1000 = .4
(2) 5600 / 1000 = 5.6
(3) .4 X 5.6 = 2.24
(4) sqrt of 2.24 = 1.49666295
(5) 20 X 1.49666295 = 29.93325
So, a 30 mm venturi is the correct size for a 2.4T.



Early_S_Man says ---------
Tall manifolds are intended to boost bottom-end torque ... that is why they were utilized on the 906 engine. Tall booster venturis are intended to capture the reversion 'fog' caused by high-overlap, long-duration racing cams, which is why they were used on the 906 engine.

Unless you are running original, early 911S cams or hotter [not '74 - '77 911S CIS engines] and SSI or early heat exchangers... you don't need the tall booster venturis. Tall manifolds could be useful on engines cammed as mild as 911E or Solex. PMO has a much better selction of manifolds than MM.

[RWebb]

If you are going to this much trouble and going to use up the amt. of gas that carbs use, you really ought to go with cams that are designed for carbs and nothing else. That means non-stock piston in your 3L, used-to-be-CIS motor.

so your list has gotten a lot more spendy right off the bat

used Webers can be a real mess - are you CERTAIN that the bushings are good?

what do the progression holes just above the butterfly look like??

40s are ok for a street motor but they are right at the edge on a 3L


replace all all rubber seals in the entire induction system

entire motor must be in good tune - that includes the advance mechanism and proper curve in the distributor.

probably want F3 emulsion tubes

need accelerator pump vial

1 synchrometer is fine - I have 2, but you don't need them - if you use 2 be sure and "cross" them to eliminate instrument inaccuracy.

a LOT of info to digest if you proceed with your own rebuild!!

there are some upgrades/mods to make too....

[911 tweaks]

well... I must say, a wealth of info here guys... thank you very much !!

Let me provode more info here as it appears that I am standing at the edge of a quite steep cliff... I bought these carbs for 3 reasons: 1. the price was fair 2. if the CIS I have almost completed restoring turns out to be a PITA and/or won't function properly I could switch to the carbs 3. I want to compare the performance differences of stk CIS vs. stk set up of webers and see what the trade offs are i.e. performance +/-, fuel consumption difference, I prefer the appearance of carbs vs. spagheti CIS 4. I am led to believe that the carbs are easier to maintain vs. cis

So, here I be at the edge. I posted a couple of threads this morning seeking what I will need to rebuild these carbs as I don't want to store the carbs w/o cleaning which means to me that I might as well rebuild them... which means that I might as well set them up as an alternative to the CIS to do the above comparisons. Maybe I am nuckin futs, but the early period car looks with carbs is what I really like...

So, maybe I need to call a carb shop and explain what the engine specs are and than order the appropriate parts ?? I would prefer to do this work myself to save on the cost a shop will charge... the throttle shafts are nice and tight... just want to clean off the crud & set em up for trying on the 3.0 engine... I also understand I will need a different fuel pump or is their a way to keep the cis tank and control the fuel pressure in the engine bay with an adj fuel pressure regulator as carbs like ~ 3.5 # of pressure and cis wants a lot higher pressure.

I will pause for a while here to see what direction this thread goes & how I should proceed.
Thank you every one.
Bob

[frankc]

Originally Posted by 911 tweaks

I also understand I will need a different fuel pump or is their a way to keep the cis tank and control the fuel pressure in the engine bay with an adj fuel pressure regulator as carbs like ~ 3.5 # of pressure and cis wants a lot higher pressure.

CIS tank and pump are fine, however you will need a fuel pressure regulator:

Our host sells one - PEL-WP31800-063

And the PMO unit is very nice - http://www.pmocarb.com/ad.htm

Frank

[RWebb]

there are many threads re putting carbs onto a CIS motor - just do a seqrch

it works but adds little power; you do get a lot of fun noises and throttle response

for power you need cams for carbs, not for CIS

what are the emissions regs for you in Mass.?? that is key to what you do.

I would not just go to a "carb shop" - you need somebody who specializes in 911s and carbs -- there are many on the W. coast; not sure re E. coast

for some reason most here seem not to realize that the cam is the fundamental key to all engine power, torque, etc. .....

speed costs money...

[JohnJL]

Depending on a LOT of variables, the following jets/bits should get you somewhere close...

57 idle jets
145 mains
180 airs
Keep whatever emulsion tubes you in there already.
Buy/borrow an LC1 or similar to tune and check your mixtures. You can then play with different jets and emulsion tubes
DC80 cams are nice but check with John Dougherty first.
You may need to go 1-2 step hotter plugs, especially when tuning to keep from fouling while making initial adjustments.

Good luck!

[911 tweaks]

Thanks Randy...
- in MA 84' or 85' and earlier are emission exempt !!! Yeah !!!
- I totally agree that cams define the personality of an engine. That being understood, I believe that the 20~21 cam is the hottest you can use with CIS due to reversion, HOWEVER, what is the hottest cam I could use if running carbs & keeping oe p/c & small port heads due to budget ?? (82' stock engine)
- any suggestions for carb work on West Coast or other parts of USA ??

Thanks also JohnJL...
- your carb set up... is this for a stk 3.0 ? I will be running oe p/c & small port heads (82' stock engine)


Maybe I should just tear down carbs, clean, re assemble and box up if all I am going to get is sound and a higher gas bill...

Thanks a lot here guys... I will researching this and appreciate any and all further info you can share here.

Bob

[rfn026]

PCA published this Weber stuff in 1992. The information is still valid. It's really a basic Weber primer.

Richard Newton
Autocross Performance Handbook

[RWebb]

Originally Posted by 911 tweaks

[1]
... what is the hottest cam I could use if running carbs & keeping oe p/c & small port heads due to budget ?? (82' stock engine)

[2]
- any suggestions for carb work on West Coast or other parts of USA ??

[1] carbs will perform well with any cam -- you can cam the motor to the point where even a teenager will tire of using it on the street within hours of their first exhilheration...

[2] I think you need more than a weber rebuild. I think you need advice - as in professional advice. As is usually the case, doing some homework beforehand and thinking carefully and critically about what you REALLY want will be important precedents to that advice.

- Consider your age, purpose of the car, presence of wife or gf, etc.

- For homework, you will want to - at last - read the engine chapters in:
- Frere, 911 Story
- Bruce Anderson's book [3rd ed. nearly ready]
- and the recommended engine types/builds in Wayne's book on 911 motors.

Remember, you can't have everything. Also, there are not many paths that have not been trod already with these motors. But, there are secret tricks at least at the race car level.

on the W. Coast some race & hotrod major motor builders are:

Steve Weiner/Gamroth - OR

?? - in WA -- John Walker does mostly conventioanl rebuilds I think. He is a nice guy and if he doesn't do hotrods, then he'll direct you to somebody that does.

SoCal is packed full of people:
Henry/Supertec - CA
Dave. B./TRE - CA
and I'm sure there are many others.

There is that guy in Nashville for those down south - he did the 964 conversion, but I forget his name...

all post here and are very generous with their time. Obviously, you would want to patronize some one who gives you a lot of help...

I dunno who does great motor mods. back East but there must be some. Bill V. or John Cramer might know.

My motor is a 3.2 with PMO carbs, SSIs, and a cowhorn Monty muffler (for a tad more noise). I still haven't put together a long thread on it, but might do that this year before the rainy season ends...

[RWebb]

oh yeh - search on "Racor" - gonna need a good filter

[911 tweaks]

thanks Randy... I will read up and postback... I am familiar with the Racor filters that i think John Cramer posted about... I am familiar with these from my boating also. They make a perfect product and is appropriate for a cis OR carb car.
The hard part if defining what the car will be... too many choices... not enough time... pelican is a savior to find out about anything for these cars :-) ... more time to think what it all will be I guess.
Thanks, Bob

[RWebb]

good luck

much cheaper to think first!

you cannot have it all - but you could put on carbs for fun & noise and do the engine work later - for real hp.

[911 tweaks]

thats the question I am trying to get answered here, Randy, how or what are the settings for setting up these carbs on a stk 3.0 CIS 82' engine that will run ssi w/ 2 in 1 out muffler... possibly 2 in/2 out m& k muffler ?? (i.e. "YOU COULD PUT ON CARBS FOR FUN & NOISE AND DO THE ENGINE WORK LATER - FOR REAL HP) !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !!!!!!!!!!!!!

So, what are the specs to set up these carbs i.e. veturri size, emulsion tubestize, jet size,... etc ???

Thanks, Bob

[RWebb]

sorry but I don't recall off the top of my head - you'll have to do a search

but you DO need to be sure the carbs are in good shape -- and that the ignition is too

[JohnJL]

Bob,
What I stated above is a starting point for a 3.0 with DR20 cams, 2-in-2-out.

That should get your started, once you finalize your other variables I and others can help with final details on jetting.

Randy also makes a good point re: ignition. You will be forever chasing your tail during tuning until your ignition is strong and consistant.

[911 tweaks]

great info here guys!
What other info can I give you so you can tell me what you need to know, so I can buy the correct carb parts (jets, venturi's, emulsion tubes,...) and finish building the carbs right after I get finished claening them up ??
Engine is stk 82' SC w/ what ever are the stk cams, ssi, 2 in / 1 or 2 out exhaust, stk dizzy.

*** To begin with, what is the most aggressive cam this stk engine can run, w/o changing p/c's, and if I need to recurve the dizzy thats fine... obviousley this set up would use the cams you recommend, what carb size jets, venturi's. ect. do I need ?? What other things can I do externally to the engine to take advantage of running carbs ??