Attached to the air horn the roch 4b has 4 tubes. 2 in the secondary accelerator pump wells on the outside, and 2 for secondary fuel air bleed on the inside. I have read to drill the outside tubes with 4 little holes starting 5/16 up from bottom. I have also read not to drill, because ounce the fuel drops below the first hole your just gonna suck air, so it says. It would seem to me that their is plenty of enough suction to overcome the little holes. The motor-craft carbs that came with the cobra jet motors had the holes, webbers and su carbs all have holes. Why the holes, if you just observe what happens here I'm in favor of the holes. With the holes as your secondary blades open, fuel starts up the tube at the top hole instead of the bottom. Better throttle response, then as the level gets lower now your introducing air into the fuel stream, air rated fuel. This aerated fuel atomizes better , or breaks apart into smaller bits, atomization of fuel. The more atomized your fuel is the more power you make. Sometimes I think the authors are paid to not promote modifications. Yes I'm sure you can drill too big a holes and mess things up. I have been running with the holes for yrs now , my carb is at the moment apart and so of course now I'm second guessing myself and wondering if I'm doing the right thing.
I'd use undrilled tubes- You don't need addl pickup area, these carbs supply enough secondary fuel undrilled to use a .030 rod, which I'm willing to bet would most cars blowing raw fuel out the back at WOT. Your transition fuel and secondary response is going to come from the pullover circuit, which does benefit from modification . I understand the aerated fuel idea, but you would definitely lean the mixture out at exactly the wrong time. and you want the fuel supply to be linear to air valve opening rate at the beginning too. Just my thoughts - do you know what your AF ratio is at WOT? might be worth checking. Keep us posted!
Kinda - o2 sensor and a gauge. There are set ups available for fairly cheap. all you have to do is weld a bung into your exhaust and put power to the gauge. I have mine as a temp set up, with alligator clips for power and ground, can move it from car to car that way. And with all that, I still chase A/F ratios and never get them perfect...
This is the one I have. Gonna have a bung welded in this Spring. http://www.summitracing.com/parts/avm-30-4100/overview/
Same one I have - I was just too lazy to go look. I got mine used on e-bay for 100.00. The bung was like 10.00, and I did the ugliest job of welding it myself you've ever seen. Thank god it's under the floor. All that said it's a good indicator - sometimes my car runs better when the gauge says it's too rich.....
Anson check with Cliff on anything about Q-JETS on his forum.He built me one it is amazing idles great with big cam http://www.cliffshighperformance.com/
The factory Pontiac Ram Air carburetors did NOT use the holes, neither did the Old's W-30, Buick Stage I's, or the Pontiac Super Duty carburetors. We have cars running deep into the 10's and some even into the 9's in the quarter mile that don't have the holes in the POE tubes, they are simply not needed. Next time that you have glass of ice tea, put a half a dozen holes in your straw and see how well it works as the level falls below the first hole, then the second, etc?......Cliff
A bit expensive for one gague, bung not included. Thanks Cliff. I started a new thread to help explain my delima.
