S&S Shorty Carb rejetting

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07-16-2018, 10:30 AM

Geir

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S&S Shorty Carb rejetting

Hope to get some assistance on this one.
Having a S&S 103" with a S&S Shorty Carb, i have now got some trouble with it after changing my camshaft.
It was equipped with an S&S 563 cam when i got it, and i have changed it to a Andrews Ev72 cam due to cam and lifter wear on the old one.
Cam comparison table:
Intake Open/Close Exhaust Open/Close Intake ExhaustIntakeExhaustValve lift
Cam1: S&S 563 -Engine:1984> 10,5:1 > - Intake Open/Close: 32⁰/64⁰Exhaust Open/Close: 64⁰/32⁰ - Intake/Exhaust Dur: 276⁰/276⁰ - Lift @ TDC ╪ Intake/Exhaust: 0,250″/0,220″ - Valve lift: 0,561″
Cam2: Andrews EV72 84-99 EVO Intake Open/Close:30⁰/54⁰ Exhaust Open/Close: 64⁰/32⁰ - Intake/Exhaust Dur:264⁰268⁰ - Lift @ TDC ╪ Intake/Exhaust:0,249″0,250″ - Valve lift:0,560″
Got the cam and ignition timing right, and i have tryed just about everything except ripping out the carb to check the Intermediate an main jet.
When starting, it sneezes in the carb AND backfires sometimes, but reving the engine it chokes unless i have got some 2000 or more revs.
Looking at the cam specs, my first thougt with this behavior is to decrease the Intermediate and main jet.

Any advice/thougts ?

Last edited by Geir; 07-16-2018 at 10:43 AM.

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07-17-2018, 06:21 AM

67drake

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I’m no expert on Harleys and never had a bike with an S&S carb. But been doing carbs on cars for years.
Your newer cam looks milder than the old one, with less overlap. I’d start by leaning out the slow jet(or whatever S&S calls theirs ) and lean out the idle mixture screw. I wouldn’t change the main till you get the idle and part throttle running right, but you very well may have to lean that out too. JMO

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07-17-2018, 02:34 PM

Hey Man

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What jets are in it now? I don't see that listed. The sneezing and back firing could indicate too much accelerator pump.

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07-17-2018, 02:54 PM

RDHIGH

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Those two cams are very similar. Your jetting should have been ok. Sneezing in the carb usually means too lean- popping in the exhaust usually means rich. The only time i had both happen at the same time was when i had an intermitant plug wire problem. Weird.

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07-19-2018, 06:15 AM

Hillsidecycle.com

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Sneezing/popping from the carb can be lean, and/or retarded timing.
A dyno tune would cure both.
Scott

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