slow jet length

[tobyp]

I am replacing a slow jet (38) keihin 07ex with a 42 slow jet and notice that the 42 is nearly 1/4" longer. Is this right? The 42 jet is flush with the bottom of the slow jet hole, before the 38 sunk in the hole about 1/4" or so. What do you guys think?

[drew416ex]

I believe its supposed to be 28mm long.

[tobyp]

Originally posted by drew416ex
I believe its supposed to be 28mm long.

ok,

I looked at the replacement jet and it is 28mm long. The original is more like 15/16" which would make it 23mm or so (since 25.4mm per inch... You think im cool with it?

**update** Just started the quad and everything seems ok.

[leasureryan]

all the stock pilots are shorter

[tobyp]

Originally posted by leasureryan
all the stock pilots are shorter

thanks for hooking me up. I cant wait for the Yoshi to show up tomorrow. Then we'll see how it really performs!!

Thanks again

[leasureryan]

you jetted it before you put the pipe on?

[tobyp]

Originally posted by leasureryan
you jetted it before you put the pipe on?

yes, I had the bike tore appart and performed the 20hr service a the time of teardown. I adjusted the valves while I had the top apart. I took the carb off and replace the needle, slow, and main since the tank was not in the way. I decided to start the bike and let it run (idle and throttle blip) for a few seconds to make sure it ran. I then removed the factory headers and slip on. I removed the spark plug and cleaned it so I could get an accurate reading on my mixture. So yes I jetted before the pipe but just for a few seconds of idle time. The pipe will be here later today.

[bigredisb]

This same question baffled 3 Milwaukee area dealers for days. I guess Honda always uses jets that are a bit different than what is widely available. I have the long jet in mine and it runs fine. In the past I was really frustrated trying to find an answer to this.

[GPracer2500]

Keihin makes a handful of different styles of pilot jet. The two in question here--the Series 21 (longer one) and the Series 26 (shorter one)--are similar but not exactly the same. The only physical difference is 4.5mm of length between the slotted end and the threads.

This is the Series 26. Pay no attention to the "applications" listing--it's hardly comprehensive. It is the stock style for the 400EX carb too.

http://www.cyclewareables.com/pages/keihin_main_and_slow_jets/keihin5.gif


The Series 21 is much more common and it will work fine in a 400ex carb. As long as there is room in the float bowl for the longer jet the effects of having the pilot fuel pickup 4.5mm lower should be too small to worry about.

http://www.cyclewareables.com/pages/keihin_main_and_slow_jets/keihin1.gif

[400ex07]

The HMF tech support says

"NOTE: you MUST use the N424-26 series Pilot jet. (It is the smaller 23.5 milimeter version) NOT the more common 28 milimeter version."

I have the 28m version in my carb. Does anyone know why HMF says not to use it?
I am having jetting issues and I am wondering if this is my problem.

[drew416ex]

Originally posted by 400ex07
The HMF tech support says

"NOTE: you MUST use the N424-26 series Pilot jet. (It is the smaller 23.5 milimeter version) NOT the more common 28 milimeter version."

I have the 28m version in my carb. Does anyone know why HMF says not to use it?
I am having jetting issues and I am wondering if this is my problem.

Who knows why they say to use that one. Im sure 99% of the members on here that have rejetted use the 21 series including me when I had the stock carb. I never had a problem with it. What kind of issues are you having?

[400ex07]

nothing major but HMF says to use a 158 and a 42 pilot, so I got the pilot went to 2.5 turns out on the screw, and I put in a Dyno jet 150 which according to the jet converter is a 165 Keihin. so that would make it rich according to their specs right?...... well the plug came out white so that tells me its lean, so I tried a dyno jet 170 which is a 190 keihin with 3.5 turns out on the pilot, that made the plug a little black but it seems really close. I think I just need to keep playing with it like I am doing, any suggestions? thanks

[drew416ex]

if you have that big of a jet in it then there has to be a air leak somewhere. You dont get into jets that size until you get into bigbores and strokers.

[400ex07]

I don't think I have an air leak, I am going to take a look, but I am starting to question the jetting converter. I followed the directions on the Dyno jet stage 2 page, that is why I tried the 170.
here is the dyno jet directions http://www.dynojet.com/pdf/Q107.pdf

I am running no air box cover along with the mods in my sig. and I am below 3000 feet.