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Author Topic:   beginner jetting questions
fastfreddy
Dirt Full Roller

Total posts: 53
posted June 10, 2005 09:15 PM  
Hey everybody, I'm new to racing, and I'm about to take my first car out in the next couple of weeks. I am just curious about carburetor jetting. I have holley jets in my rochester 2bbl, but how does a guy know if he needs different ones? The carb wasn't built locally, so I somewhat doubt it has the ideal jets for what I'm gonna do to it. Thanks in advance...

bigphillb
Dirt Roller

Total posts: 19
posted June 10, 2005 09:59 PM  
What motor, how has it been built. Gas or alky?

fastfreddy
Dirt Full Roller

Total posts: 53
posted June 11, 2005 03:38 AM  
355 9:1, pretty much stock everything except the cam and ignition. Running pump gas...

KPLugnut
Dirt Forum Champ
Total posts: 1019
posted June 11, 2005 04:29 AM  
The only way to get ya close on jets is to know everything about the carb itself as well as engine info such as compression ratio, intake, heads, cam info, etc. Air quality info is needed as well such as altitude, temp, etc.
If the carb is an 1 5/16" venturi, unmodified baseplate, with stock boosters and internals, then a 66-68 jet will get you started. If it's an 1 3/8" venturi (big bore) and all stock, then 68-72 jet, depending on your motor, etc.
As with all jet tuning, you need to fine tune on your own based on plug color, engine temp, and changing racing conditions.
The Rochesters with Holley jets tend not to need to vary in jetting more than 1-2 sizes during the typical racing season.

Hope that helps,
KP

fastfreddy
Dirt Full Roller

Total posts: 53
posted June 11, 2005 05:51 PM  
yeah, that's great, thanks a bunch

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