Jetting??? 1000cc Ironhead S&S Super E. - The Jockey Journal Board

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Old 05-08-2017, 11:51 AM   #1
WhizzbangK.C.
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Default Jetting??? 1000cc Ironhead S&S Super E.

I know it's been covered before multiple times, but this is a little different and has me stumped, so I'm hoping for a little bit of insight from the folks here.

1973 Sportster, kick only, stock cams, +.010 cylinders fresh bores, stock S&S air cleaner cover and base plate with K&N filter in it. Only thing different from normal is it's running an XLCR headpipe with baffles in it.

I've installed and tuned S&S carbs on a bunch of different bikes since the mid 80s, and never had one hurt my skull like this. I spent all day Saturday and half the day Sunday on it, and finally got it tuned and running right. Starts on first or second kick from cold (just don't use the enricher.) Runs good and pulls strong at all RPM without bogging or spitting back. Sets and idles evenly and returns to idle immediately when you let off the throttle. Sounds good, right? So what's the problem?

I ended up with a 31 intermediate jet in it. In my experience that is definitely huge for a street motor of normal displacement. I'm trying to wrap my head around why it would need such a large jet.

Suspecting an intake leak even though I did test the manifold seals when I installed it, I made a block off gasket for the mouth of the carb and installed it between the carb and air cleaner base plate. Drained the float bowl and applied air pressure (very low) to the entire intake tract. Using soapy water the only bubbles I find are slow bubbling at the throttle shaft bushings and idle mixture screw (normal since there are not o rings in those places.)

I'm having a hard time coming to grips with needing this large a jet. The only possible reason that I can come up with is that the exhaust is scavenging differently than normal (it's definitely not drag pipes) and changing the equation. Does anyone else have another idea?????? HELP
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Old 05-08-2017, 05:20 PM   #2
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Default Re: Jetting??? 1000cc Ironhead S&S Super E.

In a word ethanol. It increases fuel demand via a low specific gravity. Don't sweat the number if the bike runs well and fuel mileage is reasonable ride it. Some places are selling e15 too. That only makes it worse.
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Old 05-08-2017, 07:52 PM   #3
WhizzbangK.C.
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Default Re: Jetting??? 1000cc Ironhead S&S Super E.

I considered that, but my shovel is running fine with the same jetting I've always used (295, 71) on the same fuel that I'm running the ironhead on.
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Old 05-08-2017, 09:01 PM   #4
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Default Re: Jetting??? 1000cc Ironhead S&S Super E.

What's the plugs look like?.....and what plugs you running?
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Old 05-08-2017, 09:20 PM   #5
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Default Re: Jetting??? 1000cc Ironhead S&S Super E.

If ya wanna drive yourself nuts go ahead. If it's running well and the plugs look good what's it matter?
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Old 05-10-2017, 04:38 AM   #6
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Default Re: Jetting??? 1000cc Ironhead S&S Super E.

Measure the jet, or compare to a known good .031 jet. I have bought bad spark plugs, bad batteries, and I am sure that the same guy that built them, was in charge of stamping the sizes on S&S jets. Or, like said, forget the numbers, and just enjoy the good running motor. All motors, are not created equal. And, are you sure that the bottom is stock? It could be a stroked motor. Not to mention valve condition and cam lift/duration. All of these, affect the final jetting.

But I agree that if it is running good, and the spark plugs look good and tan, just enjoy the ride.
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Old 05-10-2017, 08:28 AM   #7
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Default Re: Jetting??? 1000cc Ironhead S&S Super E.

I'm sure the bottom is stock, I built it in 2008 and no one has been into it since. I just had the top end off and bored the jugs +.010, tested the valves, good seal still. I'm also confident the jet is correct, since I started my tuning with a 265, and worked up through 28, 295, and 31 before it quite spitting back. It is the carb that was on it when I built it, and it was running with a 295 before, which I thought was big then. I did have to clean and rebuild the carb and put new jets in it, since the owner let it set for a couple of years and the inside got crusty.

I'm just going to let it run for now, it was bugging me that it's out of the norm, but like y'all have said, if there are no leaks and it's running good, so be it. Thanks for the comments everyone.
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Old 05-10-2017, 09:38 AM   #8
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Default Re: Jetting??? 1000cc Ironhead S&S Super E.

I'm in the "if it runs great leave it" camp but have one idea for you if it'll keep nagging you.

I know later S$S E carbs have an adjustable air bleed using screw in jets (or at least have been told, I have Super Bs ;-0 ).

It's possible your air bleed to too big and you've unkowingly compensated for it with a larger main so it doesn't spit at the transition.

Jason
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Old 05-10-2017, 10:55 AM   #9
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Default Re: Jetting??? 1000cc Ironhead S&S Super E.

Quote:
Originally Posted by JasonMcElroy View Post
I'm in the "if it runs great leave it" camp but have one idea for you if it'll keep nagging you.

I know later S$S E carbs have an adjustable air bleed using screw in jets (or at least have been told, I have Super Bs ;-0 ).

It's possible your air bleed to too big and you've unkowingly compensated for it with a larger main so it doesn't spit at the transition.

Jason
My thoughts exactly.
Even though my Shorty E is an earlier model without the adjustable air bleed screw, a friend of mine who also rides a '74 ironhead had the exact same problem as the OP: One day it was running perfect with a .295/.68 combo & after he cleaned out the float bowl doing routine maintenance it would barely start.

He went the .31 jet route as well until we took the carb back to basic specs & discovered that he had fiddled with the air bleed.
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