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Pilot air jet-fcr

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Alrighty, can anyone tell me if I need to remove the pilot air jet from the FCR39? I bought the carb brand new from TT and have been watching YouTube videos and one says to take it out for sea level riding.. So I'm trying to verify it or not. My main altitude is 500 ft msl.

leave it installed and fine tune the screw . if too rich buy a smaller pilot jet .  the size is affected by engine mods, exhaust system and root diameter of the needle.

individual tuning is much better than standard jetting....

this page has a good explanation of the whole carb. the suggested method for the fuel screw is easy and effective. follow it , without opening the throlle too much, slowly from idle to about 3-4000rpm  

http://www.factorypro.com/tech/tech_tuning_procedures/tuning_FCR_Burns,Pat.html

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leave it installed and fine tune the screw . if too rich buy a smaller pilot jet . the size is affected by engine mods, exhaust system and root diameter of the needle.

individual tuning is much better than standard jetting....

this page has a good explanation of the whole carb. the suggested method for the fuel screw is easy and effective. follow it , without opening the throlle too much, slowly from idle to about 3-4000rpm

http://www.factorypro.com/tech/tech_tuning_procedures/tuning_FCR_Burns,Pat.html

Unfortunately, I don't have any rpm references. I've got an adjustable fuel screw but no adjustable pilot air jet.

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you do not need an adjustable pilot air jet. you can change the size of the pilot jet (it meters fuel) with the carb installed. it's a matter of 15 minutes and a little patience.

from the link posted above: 

 

Fuel screw:

With the carbs synched, the engine warmed up to operating temperature, and the idle speed set, adjust the fuel screws so that when you rev the bike in neutral and release the throttle, the revs quickly drop to exactly idle speed again. If, when you release the throttle, the revs hang up a few hundred rpm above idle speed, then drop to idle, the idle mixture is probably a bit too lean. Turn the fuel screws out. Use a minimum of half turn increments until you know you've just about nailed it. You'll drive yourself up the wall trying to tune the thing in eighth or quarter turn increments if you're a mile off. In extremely lean cases the idle will hunt between the proper speed and something above it. If, when you release the throttle, the revs drop below idle speed then pick up, the idle mixture is probably a little bit too rich. Turn the fuel screws in. In extremely rich cases the engine will die after revving the bike and releasing the throttle, unless you've turned the idle speed screw way in, in which case it may act like the idle mixture is a little bit too lean. In slightly rich cases, the engine will respond well to throttle blips when cold, but will die or dip slightly below idle speed when hot. While having an exhaust gas analyzer is almost mandatory during tuning of main and needle circuits, do not rely totally on them to set idle mixture. Use an accurate tachometer (like your ear) and adjust the fuel screws to find the highest vacuum for each cylinder or highest idle speed, which will often be the same setting.

 

Slow fuel jet:

After setting the fuel screws, if you end up having to turn them in closer than 1 turn out from bottomed, select smaller slow jets. If you end up with the fuel screws turned out further than 2 turns from bottomed, select larger slow jets. Go back and repeat the fuel screw adjustment procedure. You have the correct slow jets when your engine passes the fuel screw adjustment procedure (settles to a steady idle after throttle blip) with a fuel screw setting between one and two turns out from lightly bottomed. A good way to see if the slow fuel jet is too large is to slowly turn the fuel screw closed and see if the bike still idles. If you get the fuel screw down to something like half a turn out, or closed, and that cylinder is still firing, the slow fuel jet is probably too big.

 

3rd letter of the needle: This portion of the needle has the greatest effect on mixture between closed and 1/4 throttle. If the engine is too rich while gradually accelerating through 1/8 throttle, select a needle with a larger root diameter. If the engine is too lean when gradually accelerating through 1/8 throttle, select a needle with a smaller root diameter. You will drive yourself completely batty trying to sort out this if the slow fuel and air jets aren't right. Conversely, you will drive yourself completely batty if you try to sort out the slow fuel and air jets if the needle root diameter isn't right. So you're pretty much screwed either way here. And if you didn't set the float level to 9mm, just go jump off a cliff right now and get it over with because that will have a fairly large effect on how much fuel spurts up through the needle jet when the slide's only open a little bit.

Edited by 30x26
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with stock engine and cams i'd put a needle leaner than emN. 

with pilot air jet installed emp,ncyq,ncyr are more likely to work at first attempt. pilot jet around 40.

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