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FCR-MX Thumpertalk vs JD Jetting


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Hello. I bought the FCR-MX carb from the Thumpertalk store a while back and used the JD jetkit for it right away because I had good luck with the kit in the stocker. However, I felt I felt the carb wasn't at its potential. Last night I rejetted it back to the way it came from the Thumpertalk store except for a different needle and no pilot air. 

 

Right now, I have it at:

 

200 Main Air 

160 Main 

45 Pilot

removed 100 Pilot Air

EMN Needle Clip 3 from the top

 

Weather is in the 60's right now, sea level. 3x3 and free flowing exhaust.

 

Is this the correct settings for the TT FCR-MX carb? I ask because the JD kit says to leave the pilot air in, while I read in other threads that it is to be removed the way it came from the TT store if you're not using the JD kit or if the carb came off of another model bike.

 

Aside from a drastic increase in deceleration popping, the bike runs fine. I can't tell if it's better now vs when I had the JD jetkit in or not. I can only tell it's "different". One improvement however is the fuel screw has an affect on the idle now whereas even if the fuel screw was turned in all the way with the JD jetkit, my engine didn't even flinch. 

 

Anyone else have experience with jetting this thing and what works best for them? 

 

Thanks!

 

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I've got it happy at 1.5 turns out. The bike has nicer mid-range punch from what I can tell right now.

 

The deceleration popping is really consistent though.. and there's a lot of it. I think it's because of the pilot air jet removed. Is the popping alright? What's the reason of the removal anyway?

 

Thanks!

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Decel popping is normal,having a lot is not. Turn your fuel screw out to 2.5 turns out and test again. The reason why the pilot air is removed is because not enough air can get to the pilot jet. You can make it work with a smaller pilot jet with the pilot air installed but it's a big change. With the pilot air removed a 45 pj should be good for sea level up to 3000ft

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A correctly tuned pilot circuit (both pilot jet and pilot air jet) will result in virtually no popping under deccel. I get that it's not necessarily hurting anything, but it's easy enough to eliminate with some trial and error.

 

The posts I'm starting to see are starting to recommend re-installing the pilot air jet. Personally I'm running one so I could eliminate the popping, without going really large on the pilot jet. With the correct pilot air jet setting, I'm down to a 38 pilot jet without any popping.

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Ah that makes sense! With the JD jetkit, they say to leave the pilot air jet in and provide a 42 pilot to use with it. 

 

Without the pilot air, I guess I'm running leaner which causes the popping on deceleration. Is this correct? 

 

I'll order a 46, 47, and 48 pilot to play around with the carb settings. Hopefully that'll get it back to a good air/fuel mix for the pilot. (Thanks JFM43)

 

Theoretically, since there will be more fuel to accompany the increased air flow, my low end snappiness should improve, eh?

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