Alright well yesterday I installed Dynojet kit stage 2 on my 2013 KLX250s. I have a FMF Powercore4, FMF Megabomb and a Uni air filter. It runs awesome with the new jetting, but i'm wondering if it's worth it to take off the airbox lid cover?

Is it a big enough differance in power to have to clean the filter every so often or should I just keep it on? I ride in dusty conditions, that's the only reason i'm kinda debating.

Hope for your opinions, thanks

 

I would suggest riding it with the lid off and see how you like it. Personally, I found it too loud and didn't like the vibration. If there is any performance to be gained it would be minimal.

 

Like Brien said, try it. It should be a little leaner with the lid off and you should notice some performance difference, either better or worse. Mine was jetted rich (dynojet #128 main) for a time and with the lid off it would pull to rev limiter, but was noticeably rich. Put the lid on and it ran like crap at high rpms, faltering terribly around 6K rpm from an excessive rich condition. Went to a #124 with the lid off. Around 3000 ft elevation.

 

The cam mod will quiet it down some.

 

Pantyhose stretched over the airbox top could help with dust. Could be worth having a couple spare air filters, that way one is always ready to go, one in the bike, and one being washed and re-oiled.

 

Lid off is noticeably better for me. I tried snorkel out but it ran too lean and didn't pull as well. 132 main and cam mod. I can handle the intake noise. I'd rather have it a little quieter but....I won't go back.

 

Lid off is the only way to go for max power especially with your exhaust system. While I have no idea what your elevation is, what I do know from my dyno tests is that with the #132 you'll still be lean up to about 1200ft, about right (13:1 AFR) as you near 2000ft and progressively richer above. This is, of course, with the lid off. There is some evidence that "lid off" still doesn't provide enough airflow on a stock bore with our mods. Interesting deduction that "lid on" or "snorkel in" will reduce the amount of dust hitting the air filter - The only way to reduce dust exposure is by reducing airflow through the filter - perhaps with lids and snorkels...lol


I am doing a dyno shoot-out on my bike today. Full FMF (megabomb + PC4) vs stock header and DG-R. I have raised the dynojet needle one notch to try to get the AFR down closer to 13:1 as the last dyno run still showed 14-15:1 AFR using stock stage 2 with #132 jet. Report posting coming.

 

I wonder what that means.

If you expect more power and the bike is louder it's going to seem like it makes more power.

For me, it just seemed louder. I wasn't able to do anything different in actual woods riding. There could, I suppose, be some small difference on top end but I just don't ride WOT. It didn't lift the front over longs better. It didn't torque though bogs better. It was just louder while doing it.

Is it better (meaning what?, more power wot?)? Maybe. Did it make a difference in practice? No.

 

More air in an application where the intake volume is minimal from the factory...as in a tiny hole...will almost always generate more power...if...the jetting, exhaust, and other power issues are in synch and compatible with the intake volume. The small intake inlet and snorkle on the KLX is probably designed in mind for emissions/noise regulations. Obviously only a flow bench and/or dyno will correctly qualify any such results, but it is one of the oldest principles in trying to gain additional power from a 4-cycle engine. In the case of the KLX, if one mods the carb, airbox, and exhaust as much as possible/reasonable, increasing the inlet size would maximize any performance gains from those other mods. Especially when you get to the stage of increasing the displacement, it becomes even more of a benefit.

You're correct that noise alone is no indication of a power increase. However, it's a pretty good bet that the need to increase fuel delivery with richer jetting to offset the removal of the airbox lid is a pretty good indication of more air actually being used by the engine. That said, most who would consider removing the airbox lid have probably already replaced the muffler/exhaust and did some jetting mods such as a DJ kit or such. I didn't remove my airbox lid, but I did remove the screen mesh in the box and cut the hole in the lid to where it's about 2-3 times bigger.

 

How about a simple qtr mile test... Times between the mods

K.i.s.s.