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Another FCR MX setup

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Hi Eddie,

64K posts! Wow, that shows your dedication to the sport and the forum, I add my thanks. I must be a slacker as in over ten years on TT, I have 80 posts. I'm taking you up on your forum offer, so here's the info:

1)year/make/model - '07 DRZ-SM, valves in spec, leakdown 8%, fuel screw adjusted/works per post, 1.5 turns

2)conditions (elevation,temp,humidity if extreme,type of riding) - seal level-1000', 60-80F, aggresive Santa Cruz mountain runs up to Alice's Restaurant

3)modifications (pipe,air box,motor)- 434cc 12:1 JE kit, E cams, full Yosh RS2, 3x3, K&N, FCR39, Moose extended fuel screw, non-vacuum petcock

4)current jetting (the answer to this question is not "stock") - TT FCR39MX, OCEMN needle, 3rd clip from top, 160 mj, 45 pilot jet, 80 starter jet, 200 main air jet, removed pilot air jet, accel pump adjustment wired closed

5)running issue that is trying to be cured - bike warms up nicely in a couple minutes, idles nicely at 1600-1800rpm, pulls hard and clean from idle to max revs, no decel popping. Problem is just off-idle through about 1/4 throttle with NO acceleration occuring - ie level road, constant light throttle, or mid corner with cracked throttle. The bike really hunts/stumbles/jerks. Acts like a lean stumble. Add throttle or go to idle and it smooths out.

6)does the running issue change?affected by motor temp?better or worse when hot?better or worse when cold? - problem is consistent and repeatable whether bike or OAT is cold or hot.

Thanks for you input, Troy T

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Hi William, no I don't have a EMP needle, but I assume I can order one. Does it have a richer taper (smaller diameter) at off-idle? Would raising the EMN have a similar effect?

Thanks

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EMP is leaner on the straight diameter (where 95% of your 'cruising' is done). You can confirm it by moving the clip a few positions. Ignore the clip movement if it affects accleration or under load situations, just test on a flat road. If moving the clip does not make the 'no load' riding better, it is the straight diameter and the only solution is to try a different needle. To date, no one ever needed to go richer so it is a saf bet a step leaner might be the ticket. I run a EMP in the warmer weather in VA.

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Thanks for the tip. I'll test with the needle raised as well as order up a EMP. Suggestions on where to order FCR needles? What needle would be a step richer?

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PM Eddie, he can get you the needle.

FCRNeedles.jpg

So.... According to the chart, it would be a EMM. Again, we are talking about the straight diameter, the part where the throttle is at about 1/4 or less. Above that it is clip position /needle length and taper.

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Great chart, thanks for posting it, I'll add it to my jetting kit. My thinking of the problem being a lean stumble comes from the fact that adding the slightest throttle input (activating accel pump) smooths out condition, then once at steady state, it comes back. Does the rest of the jetting specs I enclosed seem in the ballpark?

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Never seen a DRZ needing more than the EMN needle. Seen a few using the EMP, a couple that ran the EMR.

When you roll on the throttle, the AP barely ozzes. Mostly, it is a bit of extra air, when combined with a slightly rich mix, runs smoother. If the bike were lean on gentle roll ons, it would fall flat on its' face. If it were way rich it would misfire/burbble like it does on steady throttle. Slight throttle apllication adds air, extra load due to acceleration savoirs a little rich. Then the fuel catches up and the stumble returns.

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removed pilot air jet

Wouldn't removing the pilot air jet cause a lean condition at closed throttle or small throttle openings?

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Yes and no. The TT FCRMX has a passage way that is the same as having a #100 slow air jet. So the slow air jet (as it comes from Sudco) is removed.

If... you did this on a non-TT store FCR-MX, it would force you to run a extremely small pilot jet. So... if you pulled the slow air jet on a carb that worked previously, the bike would probably not idle at all!

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William, your suggestion for using the EMP needle with my setup was spot on. Off-idle through 1/4 throttle has cleaned up and WOT is as clean as before. Thanks again.

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Nope. WOT is clean and crisp as is. With cold, seal leavel air, can't keep the the front tire down at WOT anyways...

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