Leak Jets

Thought I might tell you about my latest jetting adventure with my 06 FE450/FCR carb. I found that KTM and Husaberg have FCR carbs with no leak jets, whereas the Hondas and others do. For those that don't know, the leak jet is a jet in the float bowl that is in a Y configuration with the nozzle in the carb throat, effectively directing a portion of the output of the AP back to the float bowl instead of into the intake. The larger the leak jet, the less AP output the motor gets. So, it is a method of modulating the volume of the AP output. I acquired a float bowl from a 2006 CRF450R, cost: approx $50. This bowl has the place for the leak jet drilled and tapped, where the Bergs bowl is not, the location is solid metal. I figured that as I lessen the AP influence, I need to richen up other circuits. I went up one on pilot jet size, and raised the needle one notch. I am running a #70 leak jet right now. My reason for this experiment is that I have been trying to get rid of the nasty low end hesitation. Through other jetting experiments, I have it to where I am really quite happy with it, but do have a hint of stumble at high altitudes/hot days/tight trails. I believe that the AP just plain over fuels the motor when I'm on and off the throttle continuously on these snaking trails. Results: I tortured my bike, and myself to an extent, on these trails with the leak jet setup, and I do feel it is an improvement. I never got any hint of a hesitation. The jetting felt a lot more consistent, and the lower rev range felt a bit stronger (more power!). The down side, there does come a point where if you whack open the throttle at idle, it coughs. If you roll on the throttle, it acts perfectly. At any revs above idle, it acts perfectly. I have more work to do. I am going to try a #55 leak jet next, and see if it isn't the perfect compromise. This setup is sort of a middle ground between how the Beg is set up from the factory, and the folks who advocate going with no AP. I do not think that I will be going back to a no leak jet bowl, I like how it runs with the leak jet. This is not to say that any other jetting method is not right, there are many ways get an FCR to give you what you want. For the record, here is what is in my carb now: Needle NCVR pos 4, 160 MJ, 42 PJ, 70LJ. I am running the Factory Pro HDJ.

Ron,
Are you running the Honda diaphram? I thought you were. It cuts the squirt time down to right around a second. Works great for me, no hesitation, low end bog, etc.

Yes I am. Thanks for mentioning that, it is a major part in the package.

They ain't giving the R&B bowl away are they...

It does seem a nice piece of work though.

Mark

I was looking at one yesterday at Sudco. It's truely aluminum art. The adjustable leak jet runs from .35 to .85

Does it come in yellow or blue?

Sorry... red or black... :lol:

Hi Ron
since we talked in Moab I finally made the purchase. now for that bog/hesitation you
talked about you can cure that by adjusting the engagement point of the accel pump
you have lean hesitation at approx 8-9mm throttle opening ( I have not verified that
with factory pro needle jet but it is the next step) the stock carb has a engagement point
of approx 2mm and with your carb set up it does not respond very well off idle now if
make the engagement point 5,5-6mm the motor pulls much cleaner off idle and the bog when you get up in altitude will disapear
I am currently running 40 pilot 1 turn out fuel screw ( it re starts better when you are
going slow) NCVR needle 3rd pos. 165 main stock main air bleed honda accel diafram
what made you go to 160 main ? I ask this because the NCVR needle has larger tip diameter than stock, did you change the MAJ to a larger jet ?
have you attempted run without accel pump ?

happy trails Ron
Per

Howdy Buzzard,

Thanks for the updated post. Like you, once I installed the leak jet, a #55, I had a pretty bad bog problem. I was running with this set up. #40 pilot, 162 mj, NCVR @ #3, and ap gap @ .100", O ring around the ap arms,HDJ emulsion tube, and of course the Honda diaphragm.

However, unlike you, my bog problem was pretty bad. It did not go away at elevated revs. BUT, there was no rich stumble no matter how hot the bike got.

I changed the leak jet to a #35.

I went out riding/testing yesterday up at gorman which starts out at around '4000, and climed up to 6500'. Temps in the mid 80's up high and upper 90's down low, both with very low humidity. Riding was pretty tight single track, with a few jeep roads thrown in. With the #35 leak jet the bog was gone.

POINT OF CLARIFICATION FOR EVERYONE HERE. THE RICH STUTTER OCCURS JUST AS THE THROTTLE IS BEING OPENED SLOWLY, OR ROLLED ON EASY AND ONLY LASTS FOR ONE OR TWO POWER STROKE CYCLES. IT'S MORE ANNOYING THAN ANYTHING ELSE.

However, throughout the day, in various situations, mainly tight trails, where the bike got hot, I occasionally got the rich stutter again, but, like before, if you hit the throttle hard, it would take right off. It should also be noted that my buddy on his KTM 525 was having the same problem. Not surprisingly, on the jeep roads there was no rich stutter when opening the throttle.

The next move I am going to make is to increase the ap gap by 1/2 turn, or .015", aka delay the start of the squirt. In the past that has had a positive result with decreasing the stutter, but this would induce a slight hesitation when whacking it open. If I have a hesitation problem after that when whacking the throttle open, I will try raising the needle on notch. I will also go up on the pilot to a #42 as you mentioned, I'm getting a little popping on decel from mid revs. This should increase the amount of fuel pulled past the bypass in the slide under decel with the throttle closed.

But, everything one step at a time.

Everything else, other than that annoying stutter when it gets hot is great. The low end response is so much stronger than the stock settings, the bike really puches off very well. Midrange roll on is awesome as well. However, it seems that the 160 mj is a bit lean. I will experiment with a 165 mj and see how that feels.

Thanks again for all your hard work Ron, keep us posted.

Dale

One other point of interest, I did 50 miles, average speed was 18 mph, and used 6 litres of fuel in the process. That's 1.5 gallons for 33.3 mpg. Which, at that rate would have given me 80 miles of range all things being equal. I wasn't riding at a level at what I would call aggressive, and had fuel conservation in mind. But, I was still moving right along.

Don´t know if it helps you guys, but here´s a company that offers
"external adjustable leakjet" or better said "leakcircuit"
Take a look at www.mergeracing.com

Unfourtunatly I couldn´t find out pricing

Here is some new discoveries
I removed pump rod to see if and where bog started, the motor pulls clean up to 1/3
throttle and then a lean bog but the motor is much cleaner up to to that point
if you roll the throttle on fast it pulls clean to the top any faster then that and it bogs
second test Lineaweaver needle and 155 main same result maybe slightly better
now the big question would a larger main air bleed make richer or leaner when throttle
is open from 1/3 to full throttle ? it would be nice to eliminate the accel pump

VIKING

Larger main air means that your engine gets MORE air -> mixture is leaner