IDA Air Flow Between Barrels Way Off?

[Rick Parker]

markha: If you had the carbs apart it is quite possible that the throttle plates did not get reassembled perfectly and it is allowing air to bypass one of the plates when the other is closed. Best suggestion is to view through each throttle bore at a strong light source and rotate the throttle plate (noting the machined notch in each one) until the least amount of light is visable AND the plates are in the same relation with the fuel discharge hole controlled by the Idle mixture screw. The throttle plates must uncover the Idle fuel discharge hole in each bore at the exact same time (degrees of movement) and with linkage syncronized too.
If the leather seals on the outer ends of the shafts are dry or shrunk or the grease in the bearings is lacking it is possible that air can be pulled through the bearings instead of through the carb throat causing an unbalanced reading.

[racco]

your correct ida's don't, idf's do, same basic carb body. Ferrari 365bb and 512bb use four ida 3's and they have the bypass screw.

[markha]

OK. I pulled them tonight and realized that I did a bit of a rookie move. These are all Italian IDA that I bought used from various places. In rebuilding them, I did not keep the butterflys with the same carbs. No big deal... right? Well tonight I realized that some of the butterflys had been drilled with an idle correction hole and others had not. So when I reassembled them, you guessed it, I wound up with some carbs with one butterfly that was drilled and one that was not in the same carb.

So now.... do you guys run these holes? These are small (about 1mm) holes in the butterflys at the opposite site from the progression holes. I have enough butterflys that have the holes to make them all the same, but with the idle so high, I am tempted to solders these holes up.

Thanks,
Mark

[Rick Parker]

Yes plug the holes, reopen if absolutely needed. Be careful with heat on the plates they can warp. Use a soldering gun with acid fux solder. Use #242 Loktite on the throttle plate screws.

[markha]

I will have to solder them up tomorrow. After replacing the ones without holes so that the are all the same, the flow pretty close. At least with my cheesy non-scientific shop-vac flow bench, one barrel will flow at 2 and the other at 4 and this is the farthest out of sync one I have. We will see after soldering up the idle correction holes tomorrow.

Thanks,
Mark