Changing JD needle taper. Think about doing yours

[Anonymous]

I have just changed over from the JD jetting blue tip needle (pos 3) to the red tip needle (pos 5) as the hotter temps are now upon us and the air is less dense. It probably takes about 10-15 minutes to swap it out, but the results were well worth it.

To be honest I wasn’t expecting to notice much difference in performance, as my bike seems to run pretty well anyway. I was wrong! The bike was crisper and a bit more responsive to throttle changes from idle up the 3/4 full throttle. (I have marked graduations on the throttle to help with this). I found that thebike didn’t rev out cleanly on full throttle, and stumbled and burbled for want of a better description. I have very open exhaust system so have always run a largish mainjet in the FCR 39mm carby. Previously I have been running a 170MJ. The carby has also had the o-ring mod done to the AP, which comes in the JD kit as well.

I decided to play with this setting firstly dropping to a 168MJ and taking it for a run. The burbling was still there on full throttle and didn’t rev to the limiter cleanly, but it wasn’t as bad as before. It seemed that the changes were heading in the right direction, so I went one size smaller mainjet again down to a 165MJ, to test for further improvement. I took the bike for a ride on the street and it reved hard all the way to the throttle stop with no hesitation or burbling. There was some very soft popping on deceleration, but no loud bangs. I could probably play with the mixture screw to get rid of this, but at this stage the bike is going too well to want to adjust anything more. For those interested I run a 50PJ which is quite rich.

I know that test riding on the street isn’t the ideal way for jetting evaluation, but I tried as much as possible to vary the throttle position and rev and coast a bit, as one would do on the trails.

The new homemade exhaust pipe worked very well. Probably too loud for the street but only when giving the bike a bit of stick. It will be fine for the trails.I rode around the local industrial estate and held it pinned just so I could listen to the sound at full revs:P Nice and throaty!

It’s funny how everytime you pass a bunch of kids, or gang of lebbo’s on the street, they always want you to pop a wheelie. I just wish I had the confidence and skill to do so:blush:

The point of my post is basically to advise those of you who also may have JD jetting kits installed (OLLIE), that maybe now is the time to re-evaluate your current carby jetting, as you may not be getting the best from the engine.

I will remount the trials tyre back on the bike this weekend and believe or not, I may even actually attend an OBT organised ride!!!!…….one day.:silly: Might just do few short test runs out at Menai. I would attend Crash’s ride but he starts too early in the morning, plus tomorrow is the Bathurst 1000, so I will be planted in front of the idiot box all day.

Slug

[DeanMember]

Yeh nice work Nigel,I will be changing the jetting on my 450 also very soon as I originally jetted it in March when it was pissing down rain all week long and was about 11 degrees “c” I was going to change to the red tip needle and go with the 168 main currently 170 main pilot jet is 48.I have a Titanium Jardine RT4 exhaust which is also very open and have done the airbox cutouts.You have given me some good starting points cheers mate.now to get motivated and do it.

ollie

[Anonymous]

I have heavily modified my airbox, way past the standard cutouts. There is probly more airholes than there is plastic on my airbox! I also run an FMF SX Powerbomb header pipe, so I don’t know how that effects the jetting. It is supposed to drop the power curve down lower and reduce the exhaust sound level by some dB’s but neither are noticeable to my mine and I wouldn’t necessarily reccomend the product to prospective buyers. They ain’t cheap at $450+. As usual I did a contra deal to get mine cheaper.

I also should state that I haven’t installed the JD Jetting sticker on the bike yet either. That is going to add at least two horsepower depending on where it is placed on the bike. Did I mention that I have a JD kit for sale

[DeanMember]

The complete Jardine system cost me $320 delivered,from Ebay it had only done 1 round of short circuit racing,the bike as it stands now has a eye watering topend and enough bottom end also to keep me happy:laugh:

ollie

[Anonymous]

That’s a decent change from a 170 down to a 165 main. Gotta keep the bike running sweet though. Mine is running too lean as it pops quite a lot on deceleration. It will be sorted soon though

[Anonymous]

The mainjet won’t affect popping. The MJ only affects 3/4 throttle to full throttle. That is related to your pilot circuit ie pilot jet and mixture screw. I am sure there are plenty of jetting recommendations for you on KTMtalk.

[Anonymous]

Yeah I was aware of that. Just commenting that my bike runs lean and pops on deceleration. I’m pretty sure I need a bigger pilot jet but I haven’t checked what’s currently in there.

My local bike shop are doing a free re-jet for me as I bought my Wings exhaust from them I have some jetting specs that I think will suit. It will be interesting to see what they come up with.

[Author]

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