98 240sx timing, and computer upgrade

[s14280zx]

I've been tuning my 98 240 a little at a time since I bought it in 2002. So far, I've added the following: Injen short ram, Megan header,downpipe, test pipe, HKS catback, Nismo rad cap, Nology hot wires,ngk laser iridium plugs, fidanza aluminum flywheel, act xtss clutch. I've been waiting to upgrade my ecu until I get all the mods I want to do done. The way it is now it has very good power, but lately it's starting to run a little rich. When you let off going down a hill, it backfires a little bit, and I noticed above the exhaust tip the fumes made a brown mark on the paint. The exhaust smells like it's running rich. Can I change the timing to make the mixture better for the time being, or is it time for me to upgrade the ecu? I was planning on putting 91-93 cams in, a pulley set, and an ignition system upgrade (msd, or nology). What are you guy's suggestions on what I should do next? What ecu upgrade would you recommend and what should I set the timing at?

[niceguy]

You need to check your timing first and make sure your igntion system is working right (plugs/wires,etc)

After it's running right, then check into the ECU upgrade....there's lots of options. JWT is one (expensive) one that usually nets around 10whp in the midrange and a few peak from leaning things out and bumping up the timing...Others prefer the DIY tuning which works great if you know what you're doing (or know someone that does)...

BTW, my MAF connection and EGR valve (clogged w/carbon) both also caused very rich conditions and rough running but the backfiring still sounds like a misfire or timing....