Dellorto jets for an 09 GG- i'm dumb

[Addicted]

So I need to rejet my 09 280 pro. What's the long jet do? Mine is a #60. I have a #35 pilot, #118 main.

[spinnertrials]

That is the starter jet. Controls the amount of fuel that goes through the choke when it's on

[Addicted]

Cool. Thanks. So I probably don't need to mess with that one.

[Bob_M]

There are a few Dellorto carb tuning guides out there, here is one:

http://www.google.com/url?sa=t&rct=j..._U0fxdlBEMjiFA

I'm no carb genius but managed to rejet mine. I believe the long jet you show is for adding extra fuel thru the high speed starting circuit when the starting lever is lifted.

[joe cool]

I have one on my 05 Beta along with an Akro head pipe. Really made a big difference in how the bike runs.

[Addicted]

Bob, thats a good link. Thanks.

[Bob_M]

You can download a parts manual here:

http://www.trialspartsusa.com/GASGASmanuals.html

If you need help with jetting, give Stu at Jack's Cycle a call, he is a very knowlegable Gas Gas expert and a great guy. He got my bike jetted perfectly.

Jack's Cycle
72 Mountain Rd.
South Berwick, Me. 03908
Phone: (207) 337-1274

[laser17]

+1 on Jackscycles and Stu.

Std jetting recommendation from GGUSA is:
2004-05 TXT280-300 PRO WITH PHBL26 (26mm) SEA LEVEL TO 3,000 FEET
MAIN: 118 (115 OK, NOTHING SMALLER!)
PILOT: 36 (38 OK)
NEEDLE: D36 (3rd, or 2nd CLIP POSITION DOWN FROM TOP)
FUEL SCREW: 3.5 TURNS OUT
FLOAT HEIGHT: ARMS IN LEVEL PLANE WITH FLOAT BOWL BASE (PARALLEL)

My recommendation for optimal trials use is: (I live in Mass)
Main: 115
Pilot: 40
Needle: D36 - clip - 2nd from top
Fuel screw - should be around 3 turns out - but needs to be set with lean bog technique.

IMO - the PHBL likes a rich pilot for the most power off the bottom. If you want a smoother delivery off the bottom with less power then go leaner.

If you do any sustained road work or ride real fast trails - stay with the richer main and needle setting.above.

[Bob_M]

Fuel screw - should be around 3 turns out - but needs to be set with lean bog technique.


Laser17, please explain lean bog technique.

Nothing to do with growing cranberries in shallow gullies I assume

[laser17]

Hi Bob,

Basically, one way to test the fuel screw circuit is during a sudden 100% full throttle snap from idle check. The vacuum of the engine will draw fuel INITIALLY from the fuel screw circuit (the progression circuit in delortto speak) and if too lean, the engine will bog and or die. If too rich, the revs will just build slow. Its very easy to detect a lean bog , so thats what you use as a indicator - so you start from a known lean condition and work towards getting rid of it. Ideally, what you want, is enough fuel to prevent a lean condition during this wide open snap of the throttle and "just" eliminate the lean bog and alittle bit more for safety (said in Italian this sounds better)The safety adder portion should actually be tested as well - you do that with a throttle chop. Find a big steep hill (or a cranberry bog) that you can climb under WFO throttle and listen for any lean pinging after you chop the throttle at the top. If you hear any pinging, you need to richen the fuel screw more. Use this hill to verify your main jet too while your at it!

My Procedure on PHBL:
Make sure bike is good and warm. Never play with the setting with a cold bike.
Turn fuel screw in to about 1 turn out or so. (or whatever setting you know will produce a bog - you'll know it when you hear it)
Turn down idle speed to very low - enough so it doesnt stall, but very low.
Wack throttle wide open very quickly. Really make sure you get a good fast full turn snap. Listen for obvious lean bog.
richen fuel screw in 1/2 turn increments until the lean bog goes away. It will become a more subtle transition but still there.
repeat with 1/4 turn settings near point where lean bog goes away to improve setpoint accuracy. Once you find that gray zone where the bog is "just" gone - add another 1/4 to 1/2 turn richer to the fuel screw.
I find by lowering the idle way down, this really helps fine tune the "just" gone or subtle transition and I find I can get away with only adding a 1/4 turn*. The PHBL has a very sharp and defined transition so is very easy to set, so even 1/8 turn resolution of the transition is attainable once your used to it. (Unlike a VHST or even a Keihin that are alittle less defined IMO) If the weather gets really hot and humid, your safety adder from setpoint may grow from the 1/4 turn to the 1/2 turn range. (*test on hill - once found use that or be safe and use 1/2 turn)

The above can take some seat of the pants practice, but once you calibrate yourself to your bike, and you become repeatable, its' really a quick and easy thing to set just right. I will test it anytime the weather changes dramatically. Hot and humid vs cold and dry would be at least 1/2 turn different - so worth doing.

Theres a video example of this is one of the jim snell motor video's. probably the last one near the end.

After all is said and done, you should be in the 3 to 3 1/2 turn out range on the fuel screw on a average day near sea level. If not, your either jetted wrong or the carb/jets are dirty. (on a GG 250 -300 anyway)

If done correctly, the bike should have instant throttle response and the revs should drop quick too.

If you goto the NETA Trials school, Stu or I can demonstrate it as well, but im sure you'll pick it right up.
Trebor

[Bob_M]

Trebor,

Thanks for the clear and very detailed explaination. I will give this a try. This is a long way from fuel screw adjustments on 2 stroke RC model airplane engines but similar principles apply.

I am absolutely looking forward to the NETA trials school again this year.

See you there.