40mm Carb tuning - Alfa Romeo Bulletin Board & Forums
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post #1 of 35 (permalink) Old 07-28-2015, 12:24 AM Thread Starter
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40mm Carb tuning

Hi All

I'm after some carb advice. I'm rebuilding a 2l nord engine.

I've obtained some c&b 120.292 cams at a bargain price and will be using standard size valves with the seats cut as per RJ recommendations.

I'll be using standard pistons with new rings etc and I think a little skimmed of the head.

I'm told that standard practise would be to move up to 45 mm carbs with the above setup, from the 40mm carbs I have - but I have a question...

Can a 40mm carb not be modified to work as well as is needed for this setup? Or is it simply not up to the job whatsoever?

I am interested to hear if anyone has tuned/modified a 40mm carb setup to work perfectly well with a setup similar to what I am planning..

This motor is for street use only - I'm not a racer!


Thanks in advance

Last edited by swallow; 07-28-2015 at 12:27 AM.
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post #2 of 35 (permalink) Old 07-28-2015, 05:52 AM
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You don't need 45's to get the most power from that configuration and you may have low end response problems with them. My 2L motor made 169 HP @ 6200 with 40 Webers. You can instal 34mm venturis if you think that the carbs are restricting the top end power.

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post #3 of 35 (permalink) Old 07-28-2015, 07:33 AM
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No need for 45 Webers. Just need the right jet combo for the 40s.
Higher compression will help horsepower with these cams as will correct port flow.
Those C&B cams are very well liked by European Alfa builders!

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post #4 of 35 (permalink) Old 07-28-2015, 09:29 AM
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Totally agree with the above opinions. I restore plenty of 40DCOE's for 2L street performance applications. Just finished this pair of 40DCOE2's for a street/performance 2L engine customer.
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post #5 of 35 (permalink) Old 07-28-2015, 10:38 AM
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What is the cost to restore a set like that ?

Looks like new !

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post #6 of 35 (permalink) Old 07-28-2015, 11:35 AM
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If you have a decent pair to start with, the biggest costs are the actual restoration ($200 / Weber) and silver or gold cadmium plating (no longer REAL cadmium). Weber parts are not inexpensive, and that pair of 2's needed some parts for a 2L conversion.
I just did a pair of 27's for Keith Goring that were created out of a pile of parts from several core Webers. THAT was a BIG job! Sometimes the only way to get a matched pair of Italian vintage 40DCOE27's.
No paint or ultrasonic. All hand work. WheW!
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post #7 of 35 (permalink) Old 07-28-2015, 02:49 PM
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Gordon, anything against ultrasonic cleaning?

Ian

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post #8 of 35 (permalink) Old 07-28-2015, 04:28 PM
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Some time ago I was sent a pair of early 40DCOE's to repair. They had been ultrasonically cleaned by someone, at sometime, and both had more than one brass "cast-in" component, loose or leaking. I had not used ultrasonic cleaning prior to that, and decided as I did not know how ultrasonic cleaning might cause damage, continuing to clean "the-hard-way" was a safe way to continue. I DO use ultrasonic cleaning for small individual parts in some jobs, but not on the castings.


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post #9 of 35 (permalink) Old 07-28-2015, 07:08 PM
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Go to the Centerline website and you will find setup information for Weber carburetors. Confirm that you have 32mm venturis then use the standard jets.

You should seriously consider using Hastings piston rings as they bed in faster and more reliably than stock rings.

Ed Prytherch
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post #10 of 35 (permalink) Old 07-29-2015, 05:19 AM Thread Starter
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Thankyou one and all for advice on this - I shall dig out the 40's I have and start cleaning them up, see what I have - no doubt I'll be back with more questions.

All the best, Tom
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post #11 of 35 (permalink) Old 07-29-2015, 09:41 AM Thread Starter
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Gordon - those restored carbs look fantastic. Could you/would you mind, giving me a simplified walk through of the manual processes that you use to get the alloy parts cleaned up like that. From which I can youtube/google search further - it seems from some initial research that there are right ways and wrong ways - and some that say each is vice versa - all a bit confusing...
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post #12 of 35 (permalink) Old 07-30-2015, 12:08 PM
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Here's a link to an excellent carb setup guide: Daves home page

If you can still make a simple DOS program work, here's a link to an old favorite, jetting.exe. This little file makes simple work of selecting initial Weber settings: Weber Jetting Exe

By the way, I know the request was meant with good intentions, but asking someone to share all their carb rebuilding secrets when they make money by providing that specialized service puts a valued resource like Gordon in an awkward position.

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post #13 of 35 (permalink) Old 07-30-2015, 12:35 PM Thread Starter
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Thanks for those links, all useful info

Gordon has been very kind and emailed me some very useful info, pictures and tips - I don't think he's all about the money...

I'm in the UK anyway, I'd imagine shipping carbs around the world would be cost prohibitive
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post #14 of 35 (permalink) Old 07-30-2015, 12:49 PM
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Read this thread if you want to get an understanding of how engine changes affect jetting and setup of Webers http://www.alfabb.com/bb/forums/carb...da-sensor.html

Ed Prytherch
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post #15 of 35 (permalink) Old 07-30-2015, 04:46 PM
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Quote:
Originally Posted by swallow View Post
Thanks for those links, all useful info

Gordon has been very kind and emailed me some very useful info, pictures and tips - I don't think he's all about the money...
Swallow missed my point. Asking Gordon, or anyone with special expertise, to make his hard-earned knowledge public -- for free -- is the issue I was tip-toeing into, while trying to be gentle.

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