Carb Cleaning

[Mike Ramos]

So I'll open this door.  What are the best mods one can do for the FJ?  Open the stock airbox?  Junk the stock airbox?  Do either and go up one jet size to compensate for the increase in air?  Exhaust?  Cam swap?  Mine is stock right now but the potential for messing around is great.   

Good evening Gentlemen,

If I may weigh in with an opinion.

While I do not claim to know the science or engineering aspects of this subject, I believe that based on many miles of sometimes hard riding and under a wide variety of conditions, the object of the engine modifications as a whole, are not to overcome the inherent design limitations of the engine, but to maximize the performance capabilities of the design.

There is no question that for all around performance enhancement, letting the engine "breathe" more efficiently by simple changes such as advancing the ignition timing, the elimination of the air box, perhaps modest jetting changes & even a free flowing exhaust system together improve overall performance of an otherwise stock engine.

I do have all four changes and together there is a very noticeable overall improvement in engine performance.  It would seem as if one without the other(s) would not improve OR reduce the available potential in performance to such a noticeable degree.

Ride safe,

Midget.

[andyb]

I think I agree with the above, but it depends on what your desires are.  I tend to want more power everywhere, and I'm okay with losing a little smoothness and making a bit more noise.

-I'd say first, a full exhaust.  4-1 or 4-2-1, either is acceptable.  The former gives a minor flat spot around 6krpm, the latter a little less peak power.  Not much in it, either way.
-Then, I want the airbox gone.  It's not really big enough to feed a high-performance engine, and it's a pain in the backside to work around.  My choice is UNI individual filters, though the dual-pod type I understand are great (I never ran them).  Because of the interference with the frame, K&N's are junk in my opinion.  If you run UNI filters, don't over-oil them.  If you run K&N's, I'm sorry, but be VERY careful to oil them extremely lightly.
-Jetting is next, and always important, no matter what changes have been made.  I usually want a little rich at idle/cruise, slightly lean in the middle, and a bit rich on top.  For me, that'd be a 42.5 pilot, raise the needles a bit, and run a 122.5 main.
-Past that, as far as performance, an ignition advance won't hurt (+4 or so), but the better bang-for-the-buck is to buy a valve cover gasket and ensure that the cams are timed dead on.  Yeah, okay, you may need to buy cam sprockets that are adjustable.  A tiny bit this way or that can make quite a shocking change in how the powerband feels, if it's midrangey or top-heavy or so forth.

But step one, and by a big margin, is make sure it's running as well as it can run.  You don't want to be fixing problems instead of making changes on a non-correct setup.

Also, overjet it by 2 sizes on the mains and try running VP's MR12.  Yes, $30/gallon, but the power is hilarious...