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Discussion Starter #1
80% of the time when I am at a complete stop and I slam the throttle it will either die or bogg down. I have a 45 pilot, 168 main 5 clip position. I have tried to go up and down on the pilot and the main. What is the problem. I have a GYTR slip on, cam mod and lid removed.
Help please.!!!!
 

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Jetting is fun isnt it :D

To make it easier just break it down.

Bogg = too much fuel (most times)

0-1/4 throttle = pilot

1/8-3/4 throttle = needle (some believe it does have an effect beyond this range)

3/4-full throtte = main jet


Now the only problem you may have finding the circuit to adjust is that if its the needle for example it could be causing it to bogg bad enough not to allow it to be clean on the main (does that make sense? lol) and there is too much fuel already.

I am not real familar with the jet sizes on the fcr for the yfz but the main is the easiet to change so see if you can get any good results from there, and then move on to the needle or pilot jets.

And when ever having trouble with jetting always check out the whole intake and exhaust for any leaks or other things that would slow down the flow (dirty filters have messed up more than one of us).

Good luck.
 

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should try adjusting your clip position to either 4 or 3. Your current clip position seems pretty rich for the mods you have. I would also try a 48 pilot. Bogging can also be caused by not enough fuel in the pilot cuircut. These might sound contrary to each other but what in effect you are doing is richening the pilot cuircut and leaning the main cuircut.
 

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To really fix that problem, you have to remove the carb, take apart the float bowl, and change to a smaller "slow jet". I read this in a post either here, or on YFZ Central. Sorry, I can't remember which site it was. Search both sites and try to find it. I remember the guy who did it was doing a lot of experimentation with this carb and he finally got it figured out.
You could be messing with your jetting for ever trying to get it right. So far what I mentioned above is the only proper and effective method that I know of for fixing the low rpm hiccup.
 

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The jet you are referring to in the float bowl is the leak jet. It is partially responsible for controlling how much volume the accelerator pump will squirt. I was going to mess with mine but as I started adding mods and had to jet richer, the richer jetting covered up the stumble (along with my more advanced accelerator pump settings). The bog in neutral is from being too lean when you lose all velocity flowing through the carb and you could help eliminate it by advancing your accelerator pump timing, or going to a smaller leak jet, or change out the accelerator pump diaphragm for a higher output one. Some people have had good results by simply plugging the leak jet. I have not tried this yet so I cant give my personal review on this yet. If I remember right the stock yfz leak jet is a #50, the part number for a #35 which is the smallest one yamaha sells is 4JT-1494F-01-00. All I have done is advance the AP timing and while I can make it bog in neutral if I try too I absolutely cannot make it bog in gear even if I try to. FYI the yz 450 dirtbike has a plugged leak jet passageway and one part# lower output diaphragm. Happy jetting :hey: :cool:
 

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Bluenova, thanks for stating what I tried to say in a more clear and efficient manor. Unfortunately I don't remember enough of what I read to articulate it the way you just did. I may take your statement and try to remedy my low rpm stumble as well. Later
 

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What I did when I advanced my AP is I took the carb out of the rubber boots and took the right side cover off the carburetor. Then I watched how closely the squirt would come to contacting the slide when I wacked the throttle open from the idle position. I adjusted the timing screw while watching the squirts until the squirt just barely hit the slide on the way up. You can tell when it just nicks the slide because there will be a very small spot on the slide that will be wet from the gas that hit it, you cant really actually see it hit the slide so this is what I went off of. My timing screw was pretty far off from the factory and the squirt was lagging behind quite a bit and I could tell a difference while riding around that throttle response was improved after I adjusted it.
 

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bluenova...this is some interesting info you have....i was wondering if you couldnt compile a step by step procedure to do this....not all of us are very educated on the carb...like myself...i am lucky i know how to spell :lmao:
 

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I think Daddog had some good info on this subject at his site. Or was @ YFZ Central.
 

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Even if you get the jetting perfect the FCR carb doesn't like to be stabbed at because of it's downdraft style. Roll your thumb on the gas and it'll respond better. :tup:
 

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Discussion Starter #11
thanks for all the info. I just got my ESR intake and I rejetted and everything is fine now.
 

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I heard it was a downdraft style from somewhere but oh well. I tried :razz:
 
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