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Old September 2nd, 2020, 09:08 AM   #1
ssrsupermoto
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Muzzy 2 to 1 question

I previously had the stock header with JRE slipon’s. My carbs were 2.5 turns out on the fuel screw and Dyno Jet needles stock jets and sync’d using Motion pro carb sync gauges. I am running a stock air box with a stock replacement UNI filter. It’s ran absolutely perfect, I mean perfect. I recently came across and Muzzy system and I repacked it using AreaP shredded packing. Now it seems like it lost power and just doesn’t start as well as it did with the old exhaust. Is this 2 to 1 Muzzy system really that different that I need to rejet? If so what carb setups as far as jetting and where you have your fuel screws at so I can get a starting point.
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Old September 2nd, 2020, 11:32 AM   #2
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Yes, most likely you'll need to increase mid-range fuel and decrease top-end. That's due to design of 2-1 exhausts in general. They will increase mid-range torque while decreasing high-RPM power. This makes for faster and easier to ride bike on streets where low-end torque matters. While reducing that high-end scream of 2-2 exhausts.

Try:
- unscrewing pilots to 2.75 to 3.0-turns out
- add 1mm washer under needles
- reduce main-jet size by 2 to 4

Check out this thread and dyno-chart for effects of 2-1 exhaust on pre-gen. Dyno shows tremendous gain in 4-7k rpm range, with minimal increases above that.
https://www.ninjette.org/forums/showthread.php?t=13852

For best performance, you'll need dyno-test with AFR or get wideband-O2 with datalogging. On factory 250s, you can get +10% more power just by leaning out high-end mixtures by 15-20% with zero hardware changes. On new-gens, with 2-1 exhaust, they went from 105 down to 98 main-jets and it's still too rich. Using Tyga full-exhaust with straight-through muffler added +22-25% more flow and required dropping mains down to 96 for +22-25% more power. Shows factory mixtures easily have 25% too much fuel in high-end.
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Old September 2nd, 2020, 11:45 AM   #3
ssrsupermoto
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So your saying I need smaller then stock main jet size? Also I am using Dyno Jet needles that have the adjustable e-clip, What position would 1mm shim under the stock needle would that be?
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Old September 2nd, 2020, 12:16 PM   #4
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Yeah, try 103 mains, should restore more top-end. Then try 101 to see if it improves that much more. At some point, improvements will stop, go back up one size. Remember that '60s hot-rod saying...

For clip-position, middle is roughly same as stock. So with needle-tip aiming down, use slot just below middle position.
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Old September 2nd, 2020, 02:01 PM   #5
ssrsupermoto
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What brand main jets for the 103? Or better yet a part number for the 103. I am not seeing a Keihin brand main jet available in a 103. They show below 100, then 100, 102,105,108 and higher. That’s from Jetsrus.com
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Old September 2nd, 2020, 07:51 PM   #6
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MOTY - 2018, MOTM - Nov '17
Sorry, didn't look at list. Yes, 102 then 100.
Https://www.jetsrus.com/a_jets_by_ca...und_28-xxx.htm

Order of operations is to dial in optimally each stage before going to next:

- mains for high-load/high-rpms
- needles & shims for mid-range
- mixture screws for low-end & idle.

That's due to overlapping effects of each component.
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Old September 3rd, 2020, 11:11 AM   #7
Ceeloo Yello
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If I remember the cvk carb tuning paper I read it also said float height has to be set properly.
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Old September 3rd, 2020, 12:06 PM   #8
ssrsupermoto
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Float heights were set to the shop manual Specifications when I overhauled the carbs with and All Balls rebuild kit.
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Old September 3rd, 2020, 12:42 PM   #9
Ceeloo Yello
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Yes, but it said that you could adjust the float height + or - 1mm and it effects the low end power. This was the third step in tuning after best main jet and best needle height. Once again it is just what I read.
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Old September 3rd, 2020, 03:08 PM   #10
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Float height changes everything across board, idle, low-end, mid-range and high-end. It should not be used as tuning-adjustment. Because you’ll have to dial in mains, needles, pilot, idle-screws all over again after making float-height change.
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Old September 3rd, 2020, 03:28 PM   #11
Ceeloo Yello
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I'm just quoting what came with my jet kit.
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