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Thoughts on Weber 38/38

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This is all great information and I have been following this thread closely.

 

I am in a similar situation, my car currently has a 32/36 that needs a rebuild. On the shelf in the garage I also have a used 38/38 with water choke that needs a rebuild. My car has a stock 73 engine with 121 head, I have been reading through old threads to figure out the best path for reliable performance. I think either path will cost the same, but I am not an expert carb tuner so it will be a steep learning curve when it comes to swapping jets, etc.  

  • Rebuild the 32/36 and add a Sync Link so the butterflies open simultaneously? (Esty I believe in an old thread you mentioned adding the sync link to one of your cars and loving the difference?)
  • Rebuild the 38/38 and get the correct linkage from IE to run it on the car? 

I think in either situation I will need to purchase the rebuild kit, purchase some sort of linkage, and purchase some different jets, air correctors, etc. 

 

From what I have read the 38/38 is great, even on a stock engine, but will most likely be rich at idle. The 32/36 with Sync Link is an improvement but cannot match the 38/38 performance. 

 

Thanks again. 

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17 hours ago, TobyB said:

I forget what I think about the 38/38....

 

 

... but I know I posted something about it a while back.

 

I remember reading that there was very  little difference in lap times on the track between the 32-36 and the 38-38 and that the 32-36 is plenty of carb for a stock 2 liter engine.  (right?)

 

 

In my mind, the only time the difference in actual power comes into play is when you are at high rpms and additional airflow/fuel might be of benefit.  I spend very little time above 5k, so the 32-36 works just fine for me. 

 

There is a huge difference in pedal feel between the two carbs and it feeels like the 38-38 has a lot moar powa, due to the sensitive pedal.  The synchronous design brings in more fuel with less pedal travel.  That's all. 

 

Put an AFR gauge in and tune each carb and the pOwer will be about the same, since either will meet the engine's needs (capabilities).

 

Either way you decide to go, add the AFR so you actually know what you're doing/getting when you start swapping jets.  If budget is a concern, I would suggest keeping the carb you have and buying an AFR instead of a bigger carb. 

 

(there may be room for improvement on the spark side of the equation and money will be well spent on a variable timing light, if you don't already have one)

 

 

In my mind, this is a question of personal preference, mostly having to do with pedal sensitivity.  Racecars are another matter, but for a street car I prefer the progressive 32-36, where I feel like I have more control over fueling, due to the less sensitive pedal.  I also get better mileage than I would with the 38-38, which matters to me... more than it might to other people.

 

Fido barks the numbers, as  Ray likes to say.  You're gonna do what you want to do and it sounds to me like you want to buy something new.  (I'd start with an AFR gauge and a variable timing light).

 

Tom

 

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11 hours ago, jrhone said:

BUT...in my opinion it doesn't stay in tune over long periods of time and I have had 2 and have never seemed to keep them from running rich to some extent.  I think its the electric choke system not working well.

 

 

Thats very interesting, living in temperate SoCal my Tuner suggested removing the electric choke and I didn’t have seem to have jetting instability problems 

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5 hours ago, chargin said:

 

 

Thats very interesting, living in temperate SoCal my Tuner suggested removing the electric choke and I didn’t have seem to have jetting instability problems 

 

Yup the car is cranky in the morning for a few minutes then its fine.  I dont think the jets are the issue at all i think its the choke never fully engaged or disengaged and that makes the car run rich at times.  

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On 4/18/2019 at 8:49 AM, chargin said:

 

If you don’t enlarge the hole your basically choking the carb. 

I also had these questions 4 years ago, I contemplated running twin 40’s but after some research the 38/38 seemed a great route for a street build.

i set up a new 38/38 with a shorty Ireland header and had a great time with the car.

 

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Hello, I doing the exact same thing to my stock m10, I’m trying to find out which jets run the best, would you mind if I asked what you used? 

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On 4/24/2019 at 10:34 PM, Devs02 said:

Hello, I doing the exact same thing to my stock m10, I’m trying to find out which jets run the best, would you mind if I asked what you used? 

 

 

To be honest I’ve tinkered with jetting on 2 stroke race motors and was never satisfied with my results so with my 02 I just got it running and drove it to the Tuner (Le Tran) that does many of these.

 

for me it was good $$ spent 😉👍

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I love the 38/38. I have an otherwise stock 76 and I just installed my second 38/38. The first was a handmedown/loaner so I had to give it back eventually. The first carb definitely ran a little rich, but since it wasn’t mine I never fussed too much with jetting. The new one, which I tuned yesterday, has already made a massive improvement over both the 32/36 and the old 38/38. I would definitely recommend a wideband, it’ll make your life a lot easier.

And while it may not be absolutely necessary to bore out your manifold... do it. I did it myself in about an hour (including removal and installing). Just use the gasket at a guide and mark it with a sharpie. It doesn’t have to be perfect, just the right size. In fact, a coworker mentioned that a slightly rougher wall may actually have some benefits. Alternatively, drop it off at a machine shop. It’s a very inexpensive modification to have done and once you get your 38/38 on and tuned you’ll never want to go back.


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(edited)

It's used by some of the guys here on their more economical race  motors, otherwise they get bumped into a much more competitive class when running side draft carbs. But,this carb was never used by the factory or Alpina for their race motors, as money wasn't an issue for them. In my opinion, the 38/38 is a bad match for the M10 motor unless you want to run flat out. The power band and torque feel very steep and narrow wit this carb, which was designed for a six cylinder motor. I have two of these carbs, one barely used, which I never intend on using again. They also yield lousy mileage. Others here will swear by this carb, but I will never mount them on my motors again. It's probably the worst carb for the M10 motor, at least from my experience.

 

Slavs

Edited by Slavs

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9 hours ago, Slavs said:

In my opinion, the 38/38 is a bad match for the M10 motor unless you want to run flat out.

Slavs

 

Another opinion:  Part of the magic is the correct camshaft, distributor curve and tuning.

 

My experience: I can’t think of a street car I’ve worked on where - after installing a 38/38 on an M10 - someone has said, “Wait, let’s put that 32/36 back on.”  -KB.  -> will leave racing a 38/38 discussion for another time...

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(edited)

FWIW, I am running a Weber 40/40 on an otherwise stock motor and it runs great. I do have a spacer b/w carb and manifold. ('76 02)

Edited by RenaissanceMan
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2 hours ago, RenaissanceMan said:

FWIW, I am running a Weber 40/40 on an otherwise stock motor and it runs great. I do have a spacer b/w carb and manifold. ('76 02)

How's your mpg's?

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Ray  Since very few of us drive for MPG or even check it  MPG is basically insignificant  Shoot me if I ever start clogging up the roadway like some Prius driver  ( notice the next time you are on the freeway and somebody is doing 62 MPH in the car pool lane. the odds are its a Prius  but I digress. 

The difference from driving with a 32/36   and starving on the 32 single barrel and driving with a 38/38 synchronized is the low end torque is substantially greater  The car feels like it has a lot more power in normal street driving range.  The 38/38 is a lot of carburetor and can be jetted down especially for a stock motor  I run one on a mild build motor and have run one on a 150 hp build. In each case  I have jetted it smaller and they start well and run smooth.

If anyone is interested I will dig out the jetting sizes  and post them here. 

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41 minutes ago, ray_ said:

How's your mpg's?

 

Honestly I have no idea. That wasn't really a concern of mine when I bought this; I was more interested in the 'fun factor'. :) Having said that, It's not dramatically different from the 32/36, but I drive my car pretty hard.

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1 hour ago, rstclark said:

Ray  Since very few of us drive for MPG or even check it  MPG is basically insignificant  Shoot me if I ever start clogging up the roadway like some Prius driver  ( notice the next time you are on the freeway and somebody is doing 62 MPH in the car pool lane. the odds are its a Prius  but I digress. 

The difference from driving with a 32/36   and starving on the 32 single barrel and driving with a 38/38 synchronized is the low end torque is substantially greater  The car feels like it has a lot more power in normal street driving range.  The 38/38 is a lot of carburetor and can be jetted down especially for a stock motor  I run one on a mild build motor and have run one on a 150 hp build. In each case  I have jetted it smaller and they start well and run smooth.

If anyone is interested I will dig out the jetting sizes  and post them here. 

I wasn't addressing you specifically 😊

 

My point is that a 40 is overkill for a stock motor IMO 

 

Cheers,

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1 hour ago, RenaissanceMan said:

 

Honestly I have no idea. That wasn't really a concern of mine when I bought this; I was more interested in the 'fun factor'. :) Having said that, It's not dramatically different from the 32/36, but I drive my car pretty hard.

It's a lot of carb.  I ran one before. It's for sale if you need a spare 😉

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