OK, these main jets don't even look alike

[MtnEX]

OK I have several main jets my Honda dealer sold me for my EX.

However, I am looking at them and the aftermarket one that came out of the carb...

The 148 and 150 look alike... longer and hex.

Then the 152 they sold me looks like the 155 that came out of it. Much shorter and stubby looking.

What the hell?

[dalejiw25]

For "Keihin" Main Jets you want series 99101-357. These jets are 16.5mm. Long. Pilot jets are series 21 @28mm. long. Order whichever numbered jets you need out of those series only. I'd say the shortie you got sold is the wrong series Jet.

[honda400ex2003]

any pics of them? steve

[bherriman]

Yea the keihin jets will be the long hex shaped ones. Hard to tell what you have without pictures but when I had my crf250r dirtbike a purchased a fmf jet kit and those main jets were very small and round and had to use and adapter to fit the carb. It would be so much easier if jets where the same size and shape and also had some standard for measuring the bore size

[honda400ex2003]

Originally posted by bherriman
Yea the keihin jets will be the long hex shaped ones. Hard to tell what you have without pictures but when I had my crf250r dirtbike a purchased a fmf jet kit and those main jets were very small and round and had to use and adapter to fit the carb.

those are dynojets or the fmf ones at least. they are all made by dynojet and rebadged for fmf in the case. they are round ends and screw into the adaptor to make them the same as the keihin jet length of 16.5mm. steve

[MtnEX]

Thanks guys.

It had a 155 in it, which was short and round.

I picked up a 152 from the dealer and put it in... which was round also.

Then I went back to the dealer and got a 150 and a 148. These two were the longer hex ones, which at first I thought was wrong. But once I saw they would fit inside the bowl, to me they looked more right.


So thanks for helping me on that.


Now, where I may have screwed up?......

The holder came out when I removed the last jet and tried a hex one. With it being longer, I went ahead and screwed the holder most of the way in and set the lock nut.

Did I screw up there?

[MtnEX]

Oh, and when I say longer hex jets...
They look like this one in the kit...

http://www.jetsrus.com/photo_03-044.JPG

So long hex is right like you all say.

I just can't tell exactly where the holder is supposed to be screwed in to...

http://www.off-road.com/atv/400ex/images/mainjet1.jpg

That part was out a good ways.
Might be why I was having such a hard time tuning anything????

[MidnightBlade]

it's not supposed to be there at all. lol. that is for the short round jets, with the flat head screwdriver slot on them. i think...:confused:

[honda400ex2003]

I think that it is messed up somewhere but it is hard to tell. the angle is a bit weird so it is hard to tell how long it actually is. the bowl will not fit on though if there is an adaptor on it. I dont think that it could be a dynojet adaptor since the keihin style mains will not screw into the adaptor i dont think. Maybe a side on picture would be better. I was this pic earlier and just cant seem to put my finger on what it is. I will go out and take a pic after i am done eating dinner and let you see how mine is set up stock. Steve

[JOHNDOE83]

As long as everything fits no matter how tall the jet is it will work.

Ive used minkuni jets in keihin carbs, shorts, talls, round, hex.

They all work as long as it fits in the carb.

Technically you could use a bolt with a hole drilled in it for a jet if you had to, thats all it is really anyway....lol.

[honda400ex2003]

the way that you have it is correct for the keihin mains. I will post a pic in a sec. also i took a pic comparing a dj and a keihin and how they look next to each other. steve

[honda400ex2003]

Pics from a few different angles and the jets side by side. steve

you can just keep clicking on them to get them poster board size from my canon. lol.

http://img718.imageshack.us/img718/8771/img0052mb.th.jpg (http://img718.imageshack.us/i/img0052mb.jpg/)
http://img710.imageshack.us/img710/1566/img0051vh.th.jpg (http://img710.imageshack.us/i/img0051vh.jpg/)
http://img710.imageshack.us/img710/5993/img0050np.th.jpg (http://img710.imageshack.us/i/img0050np.jpg/)
http://img534.imageshack.us/img534/4759/img0049pn.th.jpg (http://img534.imageshack.us/i/img0049pn.jpg/)
http://img15.imageshack.us/img15/9180/img0048cb.th.jpg (http://img15.imageshack.us/i/img0048cb.jpg/)
http://img59.imageshack.us/img59/6814/img0047el.th.jpg (http://img59.imageshack.us/i/img0047el.jpg/)
http://img15.imageshack.us/img15/9353/img0046ic.th.jpg (http://img15.imageshack.us/i/img0046ic.jpg/)
http://img710.imageshack.us/img710/39/img0045jq.th.jpg (http://img710.imageshack.us/i/img0045jq.jpg/)
http://img707.imageshack.us/img707/7292/img0044i.th.jpg (http://img707.imageshack.us/i/img0044i.jpg/)
http://img710.imageshack.us/img710/413/img0043ok.th.jpg (http://img710.imageshack.us/i/img0043ok.jpg/)
http://img59.imageshack.us/img59/1561/img0042yv.th.jpg (http://img59.imageshack.us/i/img0042yv.jpg/)
http://img413.imageshack.us/img413/9330/img0042cf.th.jpg (http://img413.imageshack.us/i/img0042cf.jpg/)

[MidnightBlade]

steve, i like how when someone asks a question you just go and tear it off and get a pic for them. lol

[honda400ex2003]

oh it was already off and just sitting in a box. lol. I just unscrewed the bowl and took some quick shots with my camera then uploaded and posted them. no biggy lol. steve

[MtnEX]

Thanks a million... that clears it right up for me.

The jet that was in it was short, round, with a screwdriver slot... this was a 155.

I got a 152 and it was the same, short, round with a screwdriver slot.

I picked up a 150 and a 148.
These were long hex... proper jets.

All of them screwed right in the stock holder.

The stock holder backed out when I removed the 152, and I seated it deeper for the longer 150. Almost all the way in pretty much.

Can't believe the Honda shop did this crap to me and caused me this confusion. When I am back by there, I think I will stop in and show them... and have them give me a correct jet.

[honda400ex2003]

it should be all good for you now right? or do you need any more pics of it? you said it clears it up so that is good but if you need me too i can take some more it is only a few minutes to go out and take the bowl off again. remember stock is 148, 3rd needle position, 2.25 turns out on the f/a screw. I cant remember what you did anymore, but i think you added a slip on so go to the 150 and go to 3.5 turns out on the f/a screw and you should be good to go if that is the case. steve

[MtnEX]

I am good on what is what now.
I just have main jets I shouldn't have.

One wrong one that was put in with my mods (155)

And one wrong one they sold me (152)


But if you want to offer opinion on jetting I will sure as heck read it, because I am a bit flustered.

I am at 1200 ft.
I have a Yoshi full exhaust
I have a K&N with the lid on

They put in the 155 with the exhaust and K&N.

I never could be happy with it really. It started like junk. Start, die, start, die umteen times on every cold start... and it felt a bit lazy... and the plug kept getting dry black.

I could move the needle clip leaner and it would pull better, but start even worse. I could move the needle clip richer and it would start better but be worse in the middle.

So.......................

[MtnEX]

So when I had to replace some seals in the carb, I started working on jetting too.

I picked up a carb kit, a 152 main, and a 42 pilot.

It started better and all but seemed to have an occasional "stumble" if I gave the throttle just a little rapp from idle. Like if I gave it a quick blip from idle to the needle... let's say idle to 1/4-1/3 throttle.

Someone said a 42 was too much, and the plug was still showing black down around the bottom base... flat part below the threads...

So I picked up a 40 pilot and a 150 main.

Good starting is gone.
I just almost have an exhaust backfire on decel.
I am still working on the pilot screw tuning.
(very hard for me on this application)

Running seems funny to me. Seems to run strong at certain rpm's... like the front end is hunting the sky. But shift up a gear and do the same thing and it seems to be forever until it starts feeling strong.

Plug is pretty white on the porcelain, colored way down deep like it should be best I can tell. But it's still getting black on the base as before.

I don't understand the white & black together like that.
Where's the brown or gray?