What jetting do you use with Dual Pod filters?

[aigram]

I plan to install RPM's Dual Pod Foam filters onto my 1989 FJ. What main and pilot jet sizes normally work well with these filters? Is it usually recommended to add a main jet needle shim? This seems like a good time to strip away some of the emissions-era requirements that choked the 80's-90's. I'm after performance and healthy response across the throttle position range.

I understand that CV carbs are not leaned out by using these filters; the air moving through the carb throat slows down in comparison to the stock airbox, when using the dual pod filters. Honestly, I'm just looking for 'Here's what you should add to the RPM shopping cart.' Apologies if this has been well covered, I browsed through the Files section and couldn't find a "Do this" document of some sort.

[FJmonkey]

Changing jets is not a simple plug and play operation so you will not find a chart. Knowing your set up will help us get you to a good starting point. What exhaust are you running? Adding UNI filters with a stock exhaust may not need a jet change. The exhaust is also a restriction. Being able to get more air in changes nothing if you can't get it out as fast. Check the files section for some great info. http://www.fjowners.com/index.php?board=21.0

[aigram]

What exhaust are you running? Adding UNI filters with a stock exhaust may not need a jet change.

Sorry, forgot to include that I am using the stock exhaust.

[racerrad8]

... I browsed through the Files section and couldn't find a "Do this" document of some sort.

That is because there are many questions that need to be answered to get you dialed in. Everything from gearing, to altitude and rider weight.

Feel free to shoot me an email and we will get you dialed in after answering some questions.

Randy - RPM

[FJ_Hooligan]

I understand that CV carbs are not leaned out by using these filters; the air moving through the carb throat slows down in comparison to the stock airbox, when using the dual pod filters.

Half right, half wrong.

When you install less restrictive Dual Pods and remove the stock airbox, the air flow in the carbs will slow down.  That's that part you got correct.

A CV (Constant Velocity) carb is all about the Velocity of the air flow through it.  The vacuum signal that draws fuel into the air stream is directly proportional to the velocity of the air flowing through the carb.  Reduce that velocity and the vacuum also goes down (for a given throttle setting) resulting in less fuel being pulled into the intake.  Thus the air/fuel mixture is LEANER.  You would theoretically need to richen everything up; Idle circuit, Needle circuit and Main jet. 

Stock Idle jet is typically a 37.5 or 40.  Many report good results going to a 42.5 idle jet.  You also have the mixture screws to help compensate the idle circuit.

Next is the Needle circuit.  In my opinion, this is the most important circuit as it's the main fuel control circuit for a vast majority of typical riding.  To richen this circuit, you need to shim the needle to a higher position.  The lower air velocity that the Pods create cause the jet needle to sit at a lower position in the needle jet (emulsion tube).  This causes less fuel to be drawn into the intake, and thus the mixture is leaner.  Compensate by shimming the needle so it's in a higher position which allows more fuel into the intake and richens the mixture.

Finally, a larger main jet helps richen the mixture at 3/4 throttle to WOT conditions.

Avoid overdoing the jetting/shimming.  More fuel does not necessarily equal more power.  The CORRECT amount of fuel = more power.  Don't be greedy, be methodical.