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Author Topic:   Id of good rochester?
Malibu Man
Dirt Roller

Total posts: 17
posted October 22, 2005 02:10 PM  
How do you Id the better rochester carbs to run??

Are the butterflies bigger or just the venturi area??

KPLugnut
Dirt Forum Champ
Total posts: 1019
posted October 22, 2005 06:05 PM  
All the baseplates were 1.687" (1 11/16"). The largest venturi diameter made was 1 3/8". That is also the hardest ones to find these days, as there are 10 times as many 1.25" and 1 5/16" venturi carbs out there.
There were many different booster configurations available also, and as that is the "brain" of those carbs, whomever builds it has got to understand that area or it doesn't matter how big the carb is.
If you need help finding one, just hollar.

KP

Scottt
Dirt Roller

Total posts: 9
posted October 25, 2005 12:18 AM  
I ran my Rochester this past weekend and it ran like **** so I borrowed a Rochester from another racer and my engine screamed like it never has before.

I usually turn 5800rpm with my carb and I put the borrowed one on and turned 6500rpm with no other changes.

I got to have one of those carbs....He said it came off a dump truck with a vaccuum govenor. Is that what I need to be looking for?? Numbers??

KP do you have any for sale?? KP what's your web addy? I have been there before but can't remember it.

I am a new racer and everyone here runs a "Babbs Carb" and that's what I got now but this other carb kicked it bad.

KPLugnut
Dirt Forum Champ
Total posts: 1019
posted October 25, 2005 06:14 AM  
www.kineticperformance.net

I can build your carb into a "real" racing 2g for less than it takes to buy another carb, by far.

email us for details:
kineticperformance@thedirtforum.com


racing33A
Dirt Forum Racer

Total posts: 97
posted October 25, 2005 06:19 AM  
Hey KP,
I have a question for you concerning the clusters on a rochester 2bbl. I have a set that have like tin inserts in them, and I have a set that are a 1 piece casting. Which of the two are the better ones? I finally got my first true big bore rochester a couple of monthe ago. Since then I have researched almost every post you have made concerning the rochester 2bbl. I must say that I have learned a **** of a lot just by reading your posts and applying some of your techniques to my own stuff. Thanks for sharing, and keep it coming.
racing33A

KPLugnut
Dirt Forum Champ
Total posts: 1019
posted October 25, 2005 07:21 AM  
Well...."better" is a relative term. The old no-cones clusters were found in the real early (usually big bore) 2G's and do flow more air thru the ID of the booster venturi itself, but keep in mind that's only ONE piece of the complex system in there. Air bleed sizes, emulsion bleed sizes and positions in the brass emulsion tubes, squirter orifice sizes, etc all come into play, not to mention (as I'm sure you'll notice) that there are many different booster venturi height measurements. Take a look at a side view of the venturi itself and compare several of them. You'll notice lots of long ones, some mid-size ones, and some quite short ones.
Everything about how much "better" one is as compared to another has to do with how all those things work together to tailor the air/fuel ratio throughout the rpm range (known as the fuel curve).
It's impossible for me to tell you that one will be better than the other without knowing every little measurement inside each. You could swap between 10 different clusters and not notice a thing between 9 of them.
Then, factor in that many that are floating around out there have already been altered by someone over the years, and very often by someone who didn't know what the alteration was going to do, or that it was done for an entirely different use.
Some I've seen over the years honestly have looked like someone tried to do brain surgery with a chainsaw.....very ugly... :-)

Wish I had a more solid answer for ya, but there are just so many variables to it...
Thanks for the compliments, tho. :-)

KP

racing33A
Dirt Forum Racer

Total posts: 97
posted October 26, 2005 06:05 AM  
Thanks for the reply KP. In light of your answer I can conclude that if I aquired a big 2bbl and it had the solid cast one on it that it should work well with this carb.
racing33A

    

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