to slip or not to slip

[kilgoja]

ok...i'm debating whether or not it's worth it to put a slip on on my 400ex....it's not about the pipe but about rejetting the carb...i've read some stuff about having to rejet it and it seems like a pain to figure out.....more of a pain if u have to change it out when the weather changes..(summer/winter)....that would suck around here cuz in spring and fall it's cold one week then hot the next!....lol....seriously...is it really that bad...i mean with the stock jetting u can ride in any weather with no probs....shouldn't it be that way if u rejet it to match ur slip on pipe?..just looking for some real world answers and no b.s.....altitude isn't a prob since i'll always be pretty much at the same altitude...below 3000ft

[zrpilot]

Given your preferences for a "just ride it" quad, I would not add a slip-on. I would spend some money in suspension improvements though!!!!

[kilgoja]

yeah suspension was going to be next .....a slip-on first would be a lot cheaper...lol...anyone else have an opinion?

[F-16Guy]

Jetting is not hard at all, you just have to understand the process. With a good running quad, adding a slip-on should only require a one or two size main jet increase over stock, if even that. I think the 400ex is jetted pretty well stock with the exception of the pilot jet, which needs to be bumped up to at least a 40, even bone stock. So with a slip-on you would need to go to a 40 pilot (38 stock), a 150 or 152 main jet (148 stock), and I would leave the needle alone. That's a total investment of about $8 and an hour of your time. Temperature should not affect jetting so much that you see a big difference in performance. Big altitude changes are where you are going to be forced to change the main jet, regardless of what exhaust you have. A good slip-on, a high flow filter, and the correct jetting will yield some pretty noticeable gains.

[kilgoja]

ok cool...that's what i was hoping to hear...didn't make sense to me that the weather would affect different jetting since it really doesn't affect the stock jetting...it's just a matter of matching the fuel to the amount of air u got coming in ur carb to get the proper air/fuel mixture....just because the weather changes u still have the same amount of air and fuel...anyways...if i buy a slip on they tell u what jetting to use...or at least a place to start...may need a little tweaking i know...i just didn't want to be changing jets all the time...once i get it set right then it will be ok right...i won't have to mess around with it anymore......i just didn't want to do it if i'm always gonna be having trouble with it and having to mess with the carb over and over.....i just want to keep it simple as can be...so if it works like u are saying then it will be fine and it would be worth it to get a little extra power....thanks...please correct me if i'm wrong or if i missed something

i really haven't had any problems with the stock pilot jet...i did turn the idle up a little to help with starting....i usually just give the throttle a couple of blips and it cranks right up....i then barely hold the throttle down as i turn the choke off for a few secs and then i let off and it idles fine.....b4 i turned the idle up a little i would have to hold the throttle down for maybe a min before it would idle without going dead on me...does changing to a 40 pilot make it where u don't have to hold the throttle down at all?...

anyways i was looking at the motoworks slip-on pipe..on their website they recommed (if i take the air box lid off) a 170 main jet....3.5 turns out on the air/fuel mixture...and i was gonna get one of those air box covers that lets air in but keeps dirt out...does this sound good?

[F-16Guy]

Yeah, going to a 40 pilot will help a lot with starting; it's definitely something you want to do. As far as the slip on you're looking at, I can assure you that you won't need anywhere close to a 170 main, regardless of whether the airbox lid is off or not. My 416 with a K&N filter, pipe, 11:1 piston, and cam is jetted leaner than that. Like I said, you probably need a 150 or 152 if all you have is a slip on and no internal mods (piston, cam, etc.). I think manufacturers either don't take the time to come up with accurate jetting charts, or they keep it really fat to avoid liability suits.

[kilgoja]

well i think the jetting they recommend is dynojet....i know dynojet and keihin are different...not sure what keihin is equal to a 170 dynojet...i could be wrong but i think i remember seeing somewhere that it is around a 155 keihin....does anyone know?

[F-16Guy]

I have DynoJet jets in mine, and I'm at a 155 main right now. DynoJets seem to run richer than Keihins, so you would need a smaller number than you would with Keihin jets. With an E-Series slip-on, K&N filter, WB CDI, and a vented airbox, I think I ended up with a 146 DJ main (this was before the 416 piston and cam). That's actually a smaller number than the stock Keihin 148, but with the needle they give you, it seems to flow more fuel. You can try what they suggest, but then start moving down on main jet sizes and see what happens.:cool:

[kilgoja]

yeah ok...maybe i had it backwards...lol....i found a deal on the slip on ...they throw in a dynojet kit and a uni filter ...all for $299....that's pretty good since just the slip on cost $299 at other places....that way i'll have plenty of jets to try until i get it right....anyways..thanks for ur help

[400exrider707]

The weather DOES effect your jetting. The EX is a very tolerable machine though, and doesn't "SEEM" to be effected badly by changes. I usually have two different jetting situations I run. I have a summer setup and a winter setup. You are getting more air in in the winter, so your simple air in air out does change with colder temps.

Also the dynojets are bigger than the keheins so a 155 dyno is really closer to a 160 kehein. If you search, I have posted the chart numerous times comparing the two, I dont have it on my work comp so I cant just post it again, but its here somewhere!

[kilgoja]

yeah i know the weather does affect the air/fuel mixture some.....sorry but i meant that it wouldn't affect it so much as to need to rejet the carb .....i had a gas powered rc truck that had a big needle and a small needle that u had to adjust to fit different weather situations..leaner for hotter days and richer for colder days.....what i've been trying to say is that u can ride a stock atv in 95 degree temp or 30 degree....it's still gonna run fine and requires no rejetting....i've done this all my life and it never ever hurt the engine or anything......and performance was fine....on super hot days or snowy days...didn't matter....i'm not saying it was the perfect fuel/air mixture at any given time....lol...but u get my point....obiviously depending on the weather u may run a little lean sometimes and maybe a little rich sometimes....but u have the right jetting for basically any weather...kindof a balance act i guess....so basically u should be able to get the right balance of jetting to match a new pipe so that u don't have to be changing jets whenever the weather changes

now that they are putting efi into atvs....maybe that will get rid of all this guess work...lol....it just matches the fuel to the amount of air coming in....

[tar]

I can't ever tell a difference that the weather makes so don't worry about that. Yes the slip on is worth it my buddy has one and he hangs with me easily and usually beats me in drags.