HMF jetting question

[hoosierkc89]

i am getting ready to install the HMF performance slip on pipe and uni air filter on my stock 2012 400x. i was wondering where a good starting point on the jets/needle position would be. i live in Indiana, elevation is between 850-900 ft. Thanks.

[CJM]

42 pilot, approx 150-152 or so main jet, 3rd notch on needle.

[JOHNDOE83]

All exhaust manufacturers reccomend atleast a 155 main jet for their slipon.

This is just a baseline reccomendation.

You should really jet for our main jet properly, plug chopping and plug color are irrelevant when it comes to main jet tunning.

Follow the procedure at www.jetsrus.com for main jet tunning, youll have to click the link then go to the FAQ section to learn about tunning.

Other then that a 42 pilot, 3rd notch on the needle will be fine.

Like CJM said the main jet may be in the 150-152++ range.

If you dont want to try jetting procedures, get the 42 pilot, leave the needle alone and get a 155 main jet, This will be more then ok for a general carb tuning and will be fine for motor reliability.

Sometimes in the packaging for the pipe there is a 155 main jet?

[hoosierkc89]

I see a lot of people talking about doing the airbox lid delete, any thoughts on that? Thanks for the great info!

[JOHNDOE83]

That works great and is a awesome cheap mod.

A long as your not mudding or going through deep water the air box lid removal is great!

youll have to add more jetting but not much more, the 42 pilot will still be fie for this mod but your main jet will have to increase slightly.

Get your jets ready, get your slip on ready, take your lid off, then start jetting.

Its hard to say what jetts to order if you do the jetsrus method.

I would guess you need sizes from 155-175 in incriments of 5.

The bad part is, if you put the 175 in and it dont sputter on the top end youll have 4 jets your not ever gonna use. If 175 works without sputtering, I wouldnt buy more jets I would just leave the 175.

This is what I would do based on the the reccomended procedure by jetsrus and based off my jetting experiences.

Procedures and opinions vary from person to person, but I would go with what the biggest jett manufacturer/ re-seller reccomends.

[CJM]

Removing the lid does wonders as the 400 like alot of quads suffers from poor airflow. I dont like removing the box totally as sometimes in wet or muddy conditions the filter could become saturated or in rare cases if it were to fall off it would ruin your day.

I went with an EHS racing lid, uni filter and deleted the snorkel by putting a spraypaint can lid in the hole. You will be impressed with the power.

FYIL your main will need to be compensated should you remove the lid.

[hoosierkc89]

That's just the info i was looking for. Thanks, everyone. I ordered the keihin jet kit as well, so i should have any jet i am going to need

[hoosierkc89]

Ok so i got the hmf installed, i really love the sound! I also left airbox lid off and jetted.160 is the smallest main i have, but the quad seems to run very well with it. 165 didn't sputter on the top end, but seemed a bit doggy. Only issue i have is if i nail the throttle from idle it with hesitate a bit and i get a puff of black smoke out of the exhaust. I'm assuming that is because it is rich? It only seems to do it if the quad sits idle for 20 seconds or so. Would you guys just leave it at 160, as long as performance isnt an issue, or should i go ahead and order a few more smaller jets? The next lowest i have is 152, and that seems like it would be a bit too small.

[CJM]

Sounds slightly rich, a 158 might be better. www.jetsrus.com has them very cheap!

[JOHNDOE83]

hesitation might be your needle if it happens during acceleration.

To rich on the main will sputter on the top end, not in the middle not in the low end.