Experimenting with adding Leak Jet Bowl setup to FCR Carb / RFS engine

[decooney]

Question:
Just wondering if anyone here has done any real experimenting with adding a leak jet float bowl or adjustable leak jet setups to your FCR carbs on your 2005-2009 Betas. If so what were your findings and changes made, if any?

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After looking closely at the FCR carbs that came on some of the 2008 Betas with '07 RFS engines, seeing if there are some additional carb tuning opportunities recently realizing these carbs originally provided to KTM are an off the shelf carb that do not have leak jets in them like some Hondas and Yamaha's have, etc. My plan is to try out a Honda bowl with leak jet, and remove the AP shim from JD Jetting to see if I can pick up some more low end and crisp throttle response down low off-idle. We'll see how it goes.

[chasejj]

I won't ride a FCR carbed bike without one.
I run a DJH modified carb(41mm bore, BKmod HD pump chamber spring and special 3 taper needle) and a R&D Superbowl 2 which has all the bells and whistles.
With the DJH/BK mod presetting the pump squirt duration all the adjustable leak jet does is allow you to burp the airbubble that forms in the squirt chamber. In some ways my carb is overkill as Dave would(Dave installs modifies the carb by drilling some passages in lieu of using a leak jet) certainly tell you but it does work awesome. Zero hesitation, no bog. I can go from 0-5000 at least with almost no jetting or even fuel crew adjustments. I haven't tried it above that yet.
The secret to FCR's has always been the leak jet. The R&D system is the first place I would begin after establishing correct MJ/Needle/PJ setings.
I've done the BKmod on several FCR's and it is a nice addition and easy to do yourself or just send it off to Dave and have him do it all. You won't have to do anything besides bolt it on.

[decooney]

Good to know. Its worked for me on other bikes and race karts with bowls that have fixed Leak Jets like Honda runs on FCR carbs or on prior Yamaha's I've had using the adjustable pump cover setups using the stock carbs. Most of the time I would typically set it and forget it with the adjustable type, so this time around on the Beta I'm going to start with fixed leak jet / custom (FCR Honda) bowl setup to see if I can make it work. James at JD was telling me he's been able to get this to work and show up well on the dyno from bottom to top end, and on his own KTM 530, so I'll give this a try first and see if it gets me close enough. I'll hold off on the BK mod for now but may try it in the future, since I'm using the diaphram stroke shim now; that I might actually remove to start from a good baseline again. If this is still off, then maybe a fully modified carb for the open exhaust setup, and save this carb jetted down for the stock exhaust setup and those dual sport fuel saver trips. We'll see...

[decooney]

Update:

I installed the new leak jet bowl setup with #60 leak jet (added) and changed pilot and main jet closer to Stock RR setup (45 pilot), (178 main) and ODBTR needle (4th clip). I think I've found my pilot jet and main jet preference and exhaust setup. Tried the ODBTR 4th clip down from the top yesterday. The bike seems to be great off the bottom, solid midrange, and great on top-end or much better with the FMF exhaust now going back to a tad richer setup. Now I need to finalize the needle and clip setting. I am comparing back and forth between the JD Jet Red (5th clip) multi-taper needle vs. the ODBTR needle on (4th) clip.

The plan is to determine IF the JD multi-taper needle actually makes a difference or not. James at JD has indicated a good test would be between the 4th clip on ODBTR needle and 5th clip on the JD needle.

[decooney]

Observations:

Now after riding with the leak jet bowl installed using the JD Jet Red needle and the ODBTR needle comparing back and forth six times and identical 45/178 jetting on my bike I definitely notice a difference. I even switched mid-day a few times just to make sure it was not my imagination. James at JD helped me to validate my needle setting comparisons before starting.

On my bike and exhaust setup, the JD needle definitely offers more of a hit off the bottom and midrange, but sometimes more of a hit than I probably need in slick single track situations. For wide open stuff, its great to have that extra boost for sure, but I soon realized maybe more is not better in some situations where rear tires spin is not wanted as much - especially in slick single track clay type mud trails.

I started with the JD needle, then switched to the ODBTR, and noticed the ODBTR just felt smoother, not so abrupt off the bottom. Rode two times out with the ODBTR at the exact same place on the exact same trails and almost identical dirt/mud conditions. Switched back to the JD Red needle and immediately noticed the hit was back. My original demo was on a Beta RR with the same jetting and ODBTR needle, and now I know why it was just so darn smooth and predictable. It may sound strange or unbelievable, but my buddy riding behind me noticed less tire spin on one needle vs. the other comparing me riding on the same trails. I still did not want to believe it until I switched back and forth a few times.

Interesting how with a simple needle change, we can can rider-tune these bikes forth for different riding conditions.

Anyhow, it was just a goofy little experiment that proved to me there actually is a noticeable difference between the two type needles, or at least for my bike setup.

[Hawaiidirtrider]

Just to be clear here... Was there a difference you could feel between the stock setup with the ODBTR and with the leak jet bowl installed and the ODBTR? ... I'm not interested in it being more snappy down low or more aggressive for where I ride. Thanks for the info....

[decooney]

Just to be clear here... Was there a difference you could feel between the stock setup with the ODBTR and with the leak jet bowl installed and the ODBTR? ... I'm not interested in it being more snappy down low or more aggressive for where I ride. Thanks for the info....

I did this experiment in steps.

JD Jet kit first with Red needle (became noticeably snappier over stock jetting, of course). Then Leak jet float bowl next (became a tad more linear response, took away slight bog). I then tried a 45 pilot jet in between and went back to 178 main with FMF exhaust setup (definitely more power across the board). At that point, sort of realized it was a bit more to handle in single track, and started wanting to revert back a tad thinking I had taken away some of the overall smoothness and character of the bike needed in slick single track riding. Next, I tried the OBDBTR (KTM Six Days) needle and this took away some of the snap and became smoother again, but still had the low end grunt. This was totally unexpected and I did not want to believe it at first. I then left the final jetting, float bowl, and all other settings in tact and made no other changes. I then just started going back and forth between the JD Red needle and the ODBTR probably three times. Sure enough, the JD Jet multi-taper needle definitely ads snap at the low end and midrange. This was my first question I wanted to confirm. And, next was to prove what was better for riding in different conditions. I now feel the extra snap of the JD needle is not always good for me depending on what type of trails and conditions I'm riding on, and found a tad more fatigue was there at end of the day with the JD needle. On the open stuff, sure...great, works perfect. For tight and slick mud single track stuff, I'm going back to the ODBTR needle next season when the mud comes back. It was kind of a fun and interesting find for my bike setup and riding preference. I'm not sure how it would benefit others or not. Makes it quickly tunable back and forth, on my bike's setup. That JD needle sort of brought back 2T memories, including more tire spin and knobby wear. The ODBTR needle made me realize again how smooth the Beta can be when its set up a certain way, and less tires spin too.

[Hawaiidirtrider]

So I'm guessing the difference was negligible but it should work better with the leakjet bowl?.. I'm happy the way it is anyway. Maybe I'll keep these threads in mind if I want to give my Beta some fire breathing later...plus I still have my 2 stroke so I just go there when I want some braaaap.

[decooney]

So I'm guessing the difference was negligible but it should work better with the leakjet bowl?.. I'm happy the way it is anyway. Maybe I'll keep these threads in mind if I want to give my Beta some fire breathing later...plus I still have my 2 stroke so I just go there when I want some braaaap.

Yes, I think so, smoother in fact as it takes away a little bit of the bog. You don't know there is a slight bog without one until you try the leak jet setup. What I mean by bog is without the leak jet setup it just feels like there is a dip in how the power comes on. With the leak jet float bowl the power seems to come on more consistently. The jetting was constant in both tests. Now swapping back and forth between the two needles, JD or ODBTR is where I noticed the most difference in the amount of hit you get when you twist the throttle. A buddy of mine recently installed the JD needle in his. He came by yesterday commenting how the front end kept coming up in 2nd gear without even trying and it did not do that before. Like we discussed on the PM, it may be cool to have the extra power/torque for some open riding situations, but no so great for slick muddy single track trails in tight stuff. I'm betting this is partially why people are liking the new Beta 2011 Betas so much, and the 350s too, with less of a hit - making them actually faster and more easy to ride. I'm thinking we can do something similar to our RFS powered Beta 450s by actually detuning them just a tad with different jetting and/or ignition timing setups if it comes to that, etc. I use to do the same thing with 2-stroke Shifter Karts, by de-tuning them a bit and the carbs you could get them to actually bite harder and come out of the turns much faster with less tire spin. It definitely applies here as well as I'm finding out.

[RRyder]

Decooney, I love all the info you are providing. What elevation are you at? I ride at 4,000 - 8,000 ft elevation, where would the jetting setup differ at my elevation?

Thank you ahead of time, I have little to no knowledge of carb jetting. I am going to take the carb apart to see what is in there now (I'm not the original owner)

Since my move from Oregon the bike hasn't been the same. Seems low on power, harder to start, etc...