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Pilot Jet Sizes

Old 01-14-2008, 05:16 PM
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Pilot Jet Sizes

I've got a 50 size slow jet right now and it runs well. Just out of curious is there a 50S slow jet for our carbs? And if so what is the difference?

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Old 01-14-2008, 05:47 PM
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Never heard of it. Factory and Keihin use the same sizing scheme. Dynojet uses their own sizes. Maybe the "S" in 50S means slow?
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Old 01-14-2008, 06:19 PM
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yeah well my stock jet is labeled "45S" and my new pilot is labeled "50". Both are keihin brand. Just wondering exactly what the S means and if I installed the wrong "style" of jet.

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Old 01-15-2008, 07:17 PM
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Old 01-15-2008, 07:49 PM
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Originally Posted by Hawkrider View Post
Without having to dig, what carb do we have or better, main & slow (pilot) jets (Series) should I be looking at? Also, is not the 48 pilot a better choice for stock engine, filter and slip-ons?

Thanks Greg
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Old 01-15-2008, 08:06 PM
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This doesn't help much. Keihin doesn't list this carb... See attached jpg
Attached Thumbnails Pilot Jet Sizes-carbspec.jpg  
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Old 01-15-2008, 09:16 PM
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Originally Posted by skokievtr View Post
Without having to dig, what carb do we have or better, main & slow (pilot) jets (Series) should I be looking at? Also, is not the 48 pilot a better choice for stock engine, filter and slip-ons?

Thanks Greg

+1 on the 48 jets with Jardine High Mounts, K&N, 4 degree advance and the FP Ti jet kit.

50 jets were to big for my ride and caused surging.
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Old 01-20-2008, 03:09 AM
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I have run all different size pilots and mains, needles. Seat off the pants I felt 48s were right. But if I ran 48s it would run very rich on clip 5(DJ needles). Going to clip 4 caused lean stumble. I fitted a Innovate LM-1 wideband and I had to virtually screw the mixture screws right in. 45s 2.75 turns out gave me a good A/F at idle. Clip 5 with shim gave me good throttle response. On the mains I run 170 Keihin jets front and back, which gives 12.9:1 A/F.

Anything bigger too rich. I was getting 11.5 A/R at 220kmh in top with 180 mains. Not good.

Found more hp got better economy and smoother running with using a wideband and on road tuning.
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Old 01-20-2008, 08:54 AM
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Originally Posted by hymey View Post
I have run all different size pilots and mains, needles. Seat off the pants I felt 48s were right. But if I ran 48s it would run very rich on clip 5(DJ needles). Going to clip 4 caused lean stumble. I fitted a Innovate LM-1 wideband and I had to virtually screw the mixture screws right in. 45s 2.75 turns out gave me a good A/F at idle. Clip 5 with shim gave me good throttle response. On the mains I run 170 Keihin jets front and back, which gives 12.9:1 A/F.

Anything bigger too rich. I was getting 11.5 A/R at 220kmh in top with 180 mains. Not good.

Found more hp got better economy and smoother running with using a wideband and on road tuning.
I don't know what mods you are running (i.e., exhaust, filter, advancer +-, top end, etc) but its hard to believe even if you your only mod is a shimmed (? mm) +5 position DJ needle (and nothing else) that all you need are 170 mains. I only run 2Bros AL ovals (allbeit with the restriction hogged out of the oem collector) with oem air filter and oem needles shimmed .040" (and slightly worn), oem slides syncronized well under spec, oem 45 pilots about 2.5 turns out and TPS set to 500, PAIR removed and carb vent hoses repositioned, and based on dyno, plug (oem) and can tip visual readings still need 178/180 mains... and while very slightly rich here and there, he (not she) has great throttle response at all rpm, runs smooth from idle on up, no hiccups, had about +102 hp & +69 '#s (at around 25,000 miles but now has about 50k), and gets about 35 mpg average about warp 6.75 out of 10. I guess its possible but even a US oem mains are 175/178.
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