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jetting for more power

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Okay, so I went and bought & installed a 107.5 main jet, 17.5 pilot, opened the airbox, removed the screen and set everything up for a go. Oh yeah, The stock pipe has the main baffle and arrestor in but the arrestor and tip is modified for more flow. With all these mods everything worked great until I rejetted. The bike will idle, choke is functional, but once I turn the choke off and try to rev the bike it dies. My plug has a tiny bit of residue on it. I did nothing else to the carb besides try to tune pilot screw. The bike is frustrating me. What are the stock throttle screw and pilot screw settings. I've tried everything, help please.

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I had the same problem with mine after I rejetted. I bumped up the idle and moved the clip on the throtle needle up I think. Can't remember wich way I moved it but what a difference it made. I would get a different pipe for it too.

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Stalling when taking the choke off is a sign of being lean.

After changing the pilot jet, what setting did you put the fuel screw at?

I started at 1 1/2 turns out and ended up going to 2 1/2 I think. Stock the screw was only 1/2 turn out on ours and wouldn't even idle without the choke on.

Try lightly seating the screw, counting the number of turns it goes in as you do so. I made a mark on the screw and the housing to make that easier. Let us know where it is now ok?

Then, after its seated back it out 2 full turns as a baseline.

Let us know how it runs.

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I turned the pilot fuel screw in until it stops (I guess this is what you mean by seated) and then backed it out 2 1/2 turns. The motor idles fine but as soon as you crack the throttle or ease into it, it wants to die and return to idle. I turned it in one half turn and the same thing. I turned it out to three turns and no better, what gives. I have two motocross bikes and one quad and I've never ran into such a tedious change. There must be something being overlooked and not properly done. Tomorrow me and this bike are going to fight and I'm not losing!!! :cry:

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Make sure the boots the carb sits in aren't cracked or torn and that the carb is all the way in both boots and that the clamps are both tight. Be sure the air filter is installed right too. It may be a bad air leak that's leaning it out.

If that's not it, take the pilot jet you just installed out and make sure it is a 17.5 and that they didn't give you the wrong jet. Maybe try the stock 15 again to make sure the new jet isn't faulty.

Maybe the carb needs cleaning. It's possible you just got some trash in there and clogged up a jet. Maybe take out the main and pilot and squirt some carb cleaner in there and then blow it out with some compressed air. Be very careful that you don't mess with the floats when you do this.

Try turning the idle up a little.

My last suggestion is that you check the float level and possibly reset it. Maybe you accidently bent them up or down and it's just not giving enough gas.

I'm just throwing out some ideas here for you. As I said before I'm no expert at this stuff...

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I took everything apart again reinstalled the pilot 17.5 then reinstalled the main jet 107.5 and inspected everything. I next buttoned it all up and adjusted the pilot screw to 2 1/2 turns out. The bike would not start acting right until about 3 1/2 turns out. If I crack the throttle it wants to stall, but if I slowly ease into it,it will try to rev and once it gets to a certain point it will rev up really nicely. I feel I'm in the neighborhood but still not at the right house. I'm close. Any clues??? By the way so far thank you all for your help. I like learning things and not just paying a shop to do all my stuff.

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If you're at 3 1/2 before it started acting right, maybe stroker101 is right... I'd try a 20 pilot and see what happens. If you go out more than where you are now you risk losing the screw if it vibrates out.

Btw, if you're that lean on the pilot circuit, I wouldn't be surprised if you're going to need a much larger main as well. Usually the 17.5 pilot and the 110 go hand in hand from what I've seen. If you're lean on the 17.5, I doubt the 107 main will be enough. Ours was still lean with the 107, but it runs fine with the 110.

Where are you located and what are the average temps and humidity?

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I run Ultimate 4 race fuel and a 22.5 pilot jet. My worse problem is my carb seems to gum up from time to time and when it does it wont idle and pops on accel. I can't figure out what makes the carb gum up the bike is ridden at least once a week.

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I'm going to go snatch up some new jetting and go from there. By the way humidity in Northern CA really low right now and the temps are 90f. I'll give an update in a while. Thanks

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I don't think this post will help you much, but if others should read the thread, it might help. First of all, complements to TT for the detailed info on Jetting/Airbox. I purchased Jets direct from TT and received next day!! Other than an FMF Core 4 exhaust, the bike was stock. I made airbox mod, and 17.5 / 110 jet combination (2 turns on fuel screw) - what an awesome difference. The bike started in first kick and runs fantastic - just what the bike needed. My suggestion is as was suggested previously - return the bike to stock to ensure baseline and if all okay, then try the 17.5 / 110 combo - I think that is the "ticket" :cry:.

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go with a #20 or #22.5 pilot jet. install #110 thru #115 main jet. just installed a #115 m.j in my daugh. bike. runs better on top. :cry:

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Cobra,

It sounds more like an air leak. Did you forget an o-ring somewhere or something. Check your manifold.

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