Racing beat catalogue says the Weber 51ida is too big for a 12abp, but someone told me this was not true. Who's correct?

 

Both are correct………………………………



The carb will work, and has been used on 12As with great success. The stock bore size Weber will function correctly with a 44MM choke up to about 9,000 RPM. After that the metering is outside of its operating range, and a number of tricks are employed to keep the carb rich enough above 9,000. This would be the fuel pressure over 6 pounds, modified float bowl, drilled out passages, nonstock needle and seat and more.



So if you want a 51MM (bored out 48 IDF) it will have perhaps a 48MM choke and even less vacuum than the 44MM choke had, so tuning will be more difficult, and will wander around more closely tracking the weather conditions. This carb works well on a 13B with the better vacuum. About as well as a 48IDF on a 12A.



The difference on a 12A would be about 10 HP and all at the top. So if your best power right now is at 9,400 RPM, you new best power might be 9,600 RPM.



If you must go higher than that and rules are not a problem. Berg makes carbs up to 55MM that are Weber replicas with all of the changes installed already. They work out of the box (If you have enough vacuum)

And bolt to anything a Weber will bolt to. Used on sand rails and buggys. Many show up used.



Lynn E. Hanover

 

Thanks for the info, great help.