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Discussion Starter #1
As much as I would like to have a 39mm, I have more than exhausted my funds for my build :(. I got an FCR 37mm off of a 2008 CRF250R (for free :D). I'm running an athena 440 big bore, hotcams stage 2 intake and exhaust cams, mrd Pro-z pipe, and 3x3 mod. No idea how to jet this thing. Will this set up even work? How in the world do I jet it?? Many many thanks in advance
 

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Jetting for the 37mm varies. There's a few combinations that have worked for different setups. Some people use the multi-taper needles like the NCYR or NCYU. Some use the EMN or EMR needles.

Start with this:

155 - 158 main jet
200 main air jet
42 pilot jet
100 pilot air jet
EMN needle clip 3
72 starter jet
2 turns out fuel screw

The one problem that you are going to run into is the intake side of the carb. The carb that you have does not have a removable air bell. To connect the airbox to the carb, you'd have to get an FCR with a removable air bell and replace the air bell with the proper sized item. Quite a few people, especially in Europe, have successfully removed the airbox and replaced it with an intake tube and cone filter. If you want to use the CRF carb, you'll either have to do that, or make an aluminum sleeve to resize the intake side to fit the DRZ airbox boot.
 

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Discussion Starter #3
Thank you! That helps immensely! What do you mean by the air bell? I would essentially be fabricating a boot to fit the carb to the air box?
 

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This is an example of an FCR-MX with a removable intake adapter/air bell. It's where the airbox boot clamps to the carb.
The particular carb that you have, that piece is part of the body of the carb. It is a different size than your airbox boot.
If the airbox boot is not properly clamped, you will have issues. Mostly with idle.



This, here, is DRZ with a silicone intake tube and filter on the end. The airbox was removed. Yoshimura has had success with this style of setup.




This is a pic of Kevin Schwantz's old Yosh race bike. You can just barely see the cone filter peaking out from under the rear fender.
 

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Discussion Starter #5
Ahh. I see. That shouldn't be a problem for me.. What should I do with the plug that's on the carb. I think it's a throttle position sensor? Should I just snip the plug and wire it into the the plug off the stock one?

Thanks again
 

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Ahh. I see. That shouldn't be a problem for me.. What should I do with the plug that's on the carb. I think it's a throttle position sensor? Should I just snip the plug and wire it into the the plug off the stock one?

Thanks again
The DRZ doesn't need the TPS, just unplug it and leave it alone. No reason to plug it back in or try and make another one work.
 

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Discussion Starter #7
I got it up and running! Damn this thing wants to pull your arms right off! Only problem I am having is it sputters and spits a bit when full throttle in 4th and 5th gears. It will bounce off the Rev limiter in 1st-3rd with no issues but as soon as I shift up it sputters at very high rpm. I've tried main jets from 150-160 and nothing really seems to change. Right now I'm running this setup:
150 main
42 pilot
Ncyr needle 5

Think that emn needle would fix the problem? Spark plug is running pretty dark
 

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The needle isn't going to have a large effect at full throttle. Did you try air box door off? Have you tried jets larger than 160?

Reading the spark plug really doesn't work on modern fuels.
 

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Discussion Starter #9
I haven't gone over 160. I thought sputtering was running too rich? Reading the plug doesn't work with modern fuels? Not sure about that... My stock set up had a nice brown color and before I moved the needle clip on my bigbore it was white and now I did it's black...? I'm pretty new to jetting, so please forgive me if I get confused
 

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I haven't gone over 160. I thought sputtering was running too rich? Reading the plug doesn't work with modern fuels? Not sure about that... My stock set up had a nice brown color and before I moved the needle clip on my bigbore it was white and now I did it's black...? I'm pretty new to jetting, so please forgive me if I get confused
I only mention it because not everyone can tell the difference between lean / rich, both can cause the bike to "cut out".

Reading plugs is much harder with todays fuels. It's also not entirely accurate, as you ride more and have to let the bike cool before pulling the plug.

Sometimes jetting is a bit of trial and error. I tried many sets of jets before I got mine dialed in. I am running the EMN needle, but that's in my FCR39.
 

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The DRZ doesn't need the TPS, just unplug it and leave it alone. No reason to plug it back in or try and make another one work.
This is definitely false information, guys.
Tps sensor is a very important sensor.

It turns on the ignition according to the position of the throttle and ensures an accurate combustion.
Do not mislead people in matters you are not sure.

 
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