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not much of a power difference with FCR MX carb

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First of all I want to thank all you TT members and Eddie for posting so much usefull information about installing the TT FCR MX carb. The job went super easy. Thanks.

Now a problem. When I am cruising down the road flat surface any gear with about 1/8 to 1/4 throttle the engine starts to backfire and surge. I can only describe the feeling as, it feels like it is running out of gas. When I close the throttle under decel the bike has some backfire in the low rpms not the high.

Everywhere else it runs ok, 1/4 throttle up to WOT. Does not like to cruise down low. I am not lugging the engine, just steady rpm's. I pulled the carb and dropped the clip down one notch. I am at the 4th notch from the top now. A little better but still the same end result.

I pulled the airbox cover and went for a ride, did not feal any difference at all, except more noise. I was reading about people lifting the front in 3rd gear. Mine can barely pop it up in second, even then I have to try hard and pull hard to get it barely up a little. The Mikuni with JD kit, made more ponies, so I know something is wrong.

List below is my exact specs..........

2008 SM, 1,500 miles, Valves in spec. 89 octane

TT FCR MX carb, pilot air jet removed, EMN needle 4th clip from the top, O-ring mod, fuel screw exactly 2 turns from closed.

Yoshimura TRC full exhaust

3x3 mod

Uni air filter

Air temp 79 degrees

Humidity 20%

Elevation- sea level

anything else?

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Move the needle to the 2nd from the top and retest.

So your thinking that I am too rich with my current needle set-up. Feels lean to me, but easy enough to try it out.

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then you dont know that is making less or even more "ponies".

do you have the insert out of the pipe?

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then you dont know that is making less or even more "ponies".

do you have the insert out of the pipe?

Yep, insert removed from pipe. Power difference comes from seat of the pants, but it's big enough to "feel" the difference. Something has to be wrong, I am out of solutions. Going to move the clip to second position from top as suggested earlier.

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If it's really backfiring and surging like it's out of gas, then doesn't that sound like a vacuum leak somewhere? Even if your jetting is off, you shouldn't be experiencing anything like that.

Check to see if the carb is properly seated in the air boot.

Your thread title is misleading because it sounds like you feel like your not getting a lot of power out of the FCR, when what you are actually describing is some kind of problem.

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not misleading, just two different problems all together. Running poorly and lack of power vs stock carb with same mods. Intake boot is mounted correctly and clamps are tight, just checked.

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you did no other work?

3x3 mod done? exactly 3x3?

did you have the slide out of the carb?

Yes exactly 3x3. I did not pull the slide out of the carb. One noteable mention, after I hooked it all up and went to twist the throttle it, the slide was binding going back down, it did this a few times then stopped. Felt like it had a burr or something holding it up. It was definately the carb and nothing else binding, I checked. Maybe there is something blocking a passageway? How far should I go taking this carb apart. I don't want to damage anything.

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Yes exactly 3x3. I did not pull the slide out of the carb. One noteable mention, after I hooked it all up and went to twist the throttle it, the slide was binding going back down, it did this a few times then stopped. Felt like it had a burr or something holding it up. It was definately the carb and nothing else binding, I checked. Maybe there is something blocking a passageway? How far should I go taking this carb apart. I don't want to damage anything.

can you see the 1/4" hole in the slide plate when look in the motor side of the carb?

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Regarding the stocking throttle, the throttle wheel may of been touchuing a frame tube.

It was definately the slide. The first time I felt it I stopped twisting with the throttle tube and opened the slide with the pulley, you could feel it bind up as it went back down slowely. It was catching on something, then a hard skip past it. The slide would almost stay up by itself. Did this only a few times then went away. Not sure if that is related to my problem.

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can you see the 1/4" hole in the slide plate when look in the motor side of the carb?

Just pulled off the carb, yes I see it plain as day.

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Also I just checked the pilot and main fuel jets to confirm their size. 160 on the main, 45 pilot jet. Took them off and inspected them. No problem there. I still need to run the bike with the clip on the second groove from the top. Going to reinstall the carb and go try it.

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not misleading, just two different problems all together. Running poorly and lack of power vs stock carb with same mods. Intake boot is mounted correctly and clamps are tight, just checked.
was your stock carb have a jet kit in it?if it did and you had already done the 3x3 then when you put on the fcr you will feel a difference but not a huge difference.fcr&3x3 adds about 3hp,stock carb with a jet kit & 3x3 about 1.5hp.add a pipe to the fcr 3x3 you get about 5hp and 2.5 with the stock carb jetted and 3x3 and a pipe

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:D:worthy: I have to revoke my previous statement. I went to the second clip on the needle and this thing RIPS! Wow it's fast. I can't believe the carb can change that much from such a simple clip movement. Went from a old lazy dog to a fired up lion. All the surging is gone too. I still am getting quite a bit of loud popping on decel that it never did with the Mikuni.IS THIS NORMAL? Thanks William, you hit the problem right from the start on the first try. Thanks to everyone elses input. Greatly appreciated.:)

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