Weber Carb Questions...

[Dave75verona]

Hi...Have to Weber Carbs on hand and wanting to install one to boost performance. But I'm not sure what to expect with these two and wanted to see if there are any benifits between the two models.

They are marked as the following:

40DFAV

38DGAS

I'm planning on installing these with a cannon intake, but also have a couple questions about that intake, but will put them on another thread.

I'm also in possesion of a duel 40 webers and was considering intalling those, but concerned with regards to MPG. If anyone's got any idea what kind of power I'd get with running duel carbs and what kind of MPG I'd be getting, I'd like to hear from your experiances. I've got a mild cam in there so it would be a fun ride.

Thanks for your help...Dave.

dave75verona@yahoo.com

[BarryA]

along with what other mods are present (beyond the cam), as well as how well you're able to tune the carb(s) you decide to use to the engine.

The 38 will certainly work well if the engine is in otherwise good condition - all other things being equal, you'll probably find that the larger carbs will give you somewhat better performance at the top end of the rpm range, at the cost of somewhat more sluggish low rpm response. Unless you have pretty extensive modifications (higher compression, headwork, radical cam, headers, etc), you may find that dual 40's are overkill.

As for fuel economy, my 69 with mild engine mods (9.1 compression, Schrick 284 cam, minor head work, tii distributor & exhaust manifold, 2" exhaust) OD 5 speed, 3.64 diff and 185/70x13 tires consistantly turns in mid to high 20 mpg at about 3500 freeway rpm, & high teens / low 20's around town (depending on how often I put my foot in it).

[Dave75verona]

Thanks for your help Berry...I was wondering if you've worked with the jets on your carbs, cause I'm looking to get some jets and work with the carb and my setup to find the most optimal jets. First problem I'm having is finding the jets.

Thanks...Dave.

[BMWonly]

I usually order my jets from Carbs Unlimited. Good prices, fast shipping:

http://www.carburetion.com/index.htm

I have a 71 Opel GT with a 2.0 and 38 Weber, so very similar to the 2.0 M10. It took me a while to get the jetting right. I am running 130 mains and 60 idle jets. Depending where you got the Weber from, it might have a 6 cyl. emulsion tube (F50), you need the F66.

Dieter

[Fishhead]

I'm also in possesion of a duel 40 webers and was considering intalling those, but concerned with regards to MPG.

I've also read that the dual Weber carbs kills the gas milage too and I'm curious to how much MPG is lost over the typical twin barrel carb.

On my CB 750 SOHC with a RC Engneering manifold with dual DCOE40's (30mm venturis, otherwise stock engine), the performance went up and so did the gas milage. The stock Keihin 28mm carbs would get 45-48 MPG and with the Webers I'm getting up to 55-ish MPG.

Fishhead

[TobyB]

It's all down to tuning.

A carefully tuned set of 40's with smaller chokes will be able to get well into

the 20's, and maybe up to low 30's if you are careful with both tuning and

how much you use your right foot.

The 38/38 actually presents a LOT more throttle plate area than a 40 dcoe.

Combined with the plenum intake, theoretically it isn't as efficient...

Really, if fuel economy matters, stick with the 32/36- you get most of the performance

and it's easier to tune for both, since you can make the -36 barrel pretty fat

and not really hurt economy.

Otherwise, have fun.

alfa1750 on ebay has always come through with jets, and about a 2- week turnaround.

t

[TTyMiller]

Toby,

What is the set up and jets for that kind of fuel saving. I ask this because I want to go duel 40s and have them also a 38/38 and a 32/36.

My fuel comsumption with the 38/38 sucks and Ireland jetted that for me knowing it's a street car.

I pull great with the 38/38 but those 40s keep calling me

[rover1]

you cant blam ireland for that, jetting a carb is not a one size fits all type of thing.

[TobyB]

ok, best answer is to get a wideband o2 sensor and meter and do it yourself.

But since I put foot in mouth, here's a starting guess- with 40's,

30mm chokes, 50 progressions, 120 mains, 190 air correctors.

Honestly, your economy will come from the progressions

AND WHAT KIND OF PROGRESSION DRILLINGS YOUR CARB HAS!!!

Weber stuck you with them, so you have to make them work, and some

just don't.

If it runs well on 50's, try 45's. If it runs well on 45's go down to 40's.

Smaller=leaner=better economy AT THE SAME THROTTLE OPENING.

It's very wise to log revs and throttle position (a la LM-1) so you can compare. But that's expensive...

As you choke down, you increase the 'suck' that the carb has to pull fuel,

so you can jet down, too. So if you find 28mm chokes, try smaller jetting

and maybe larger air. But seriously, the wideband and your butt will

work together to give you decent drivability AND really good economy.

You theoretically can tune way lean on the progressions and transition to

a neutral main, then fatten with a small air corrector and get good economy

AND real power. But you'll have to find it by tuning. The wideband

makes it a LOT easier and quicker, as it helps you figure out 'what'd I do?'

when you make a jet change.

Wish there was a one-size-fits-all answer, but there's not...

t

[TTyMiller]

you cant blam ireland for that, jetting a carb is not a one size fits all type of thing.

I didn't say I was blaming Ireland for anything. I don't know if that's just standard for the 38/38 or not that's why I'm asking questions.