Reverae jetting

blaster801 · 07-22-2009, 03:26 PM

This is for Bill!!!
Can you please give me a technical explaination about the need to jet a carb with a pilot bigger than the main (reverse jetting)?
My idea is that this practice is useful only in highly modified engines that have big demand of fuel in the midrange and so you are forced to increase a lot the pilot jet.
What do you think?
Any input is welcome||
Thank you
Michele

Bill O'Neal · 07-23-2009, 01:52 PM

Reverse jetting can work with some carb sets in certain applications, but not all applications. I have run reverse jetting in some 787 racing boats many years ago. I have not used reverse jetting on any 1050 race motors though, so I do not know wether it would benefit you with your motor.
There is only one way to find out if it will work, and that is to take a handfull of different low and high speed jets and a couple of different spring sizes to adjust pop off pressures, to the lake and spend a day or two testing.
I suggest that if you have Novi carbs, you run it by Tim Vaughn first. He can tell you if it is worth trying, or if you would be barking up the wrong tree.

blaster801 · 07-23-2009, 05:19 PM

Hi Bill,
Thank you for your answer but I would know the tech explaination about the need of reverse jetting............Can you help me?
Thank you
Michele

Bill O'Neal · 07-23-2009, 07:21 PM

The "technical explination" is that if it needs more fuel on the bottomend to make it accellerate well, you then to to compensate with smaller jetting on the high speed jets so that the motor is not getting too much fuel overall.
When it gets to the point that the low speed jets are larger than the high speed jets, you have reversed jetting.

blaster801 · 07-24-2009, 06:08 AM

Thank you Bill!!
Michele