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Old 09-19-2012, 08:01 AM   #1 (permalink)
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Engine Run-on

So, I get into work this morning and shut off my bike and the engine continues to run for about 4 sec.

I've looked around a bit and see when folks have discussed this on other forums. I've seen people blame:
1. poor gas.
2. too advanced timing. One poster on another board suggested that Harley ships the Sportster with the timing advanced 2 degrees further than it should be.
3. too rich of a slow jet.

I run 93 octane and always have. I don't think I buy the timing too advanced by factory theory.

When I replaced my drag pipes with stage I mod stock pipes, I was running too rich and had to close down the jet. So I am running 1-3/4 turns out on a .48 slow jet. I guess I could re-jet it back to the .45. But I haven't had any issues until today.

Any sage advice out there?

Thanks.
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Old 09-19-2012, 08:06 AM   #2 (permalink)
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Run-on is caused by:

Fuel supply....with excessive heat to ignite it. (That's why it's called "Dieseling".)

The engine can't run without fuel.

Fuel doesn't burn without spark/heat.

Venturi vacuum can pull fuel from carb.

Start looking at heat related issues, like leaking intake seals, or something creating excess heat. (Lean)

Timing can contrinbute as well, but so can plug heat range and gap.
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Old 09-19-2012, 08:08 AM   #3 (permalink)
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Gap too wide or closed Dave ?
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Old 09-19-2012, 08:11 AM   #4 (permalink)
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I did just install SE plugs and wires last weekend. Think that's a contributor?
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Old 09-19-2012, 08:11 AM   #5 (permalink)
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Too close/tight. Causes pre-detonation.
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Old 09-19-2012, 08:12 AM   #6 (permalink)
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Quote:
Originally Posted by Fuzzy66 View Post
I did just install SE plugs and wires last weekend. Think that's a contributor?
Did it do this BEFORE the plug/wire install?
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Old 09-19-2012, 08:16 AM   #7 (permalink)
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No, I recall once the engine might have made like a 1 revolution run-on after engine shut off. But it was a really hot day, so I didn't think much of it.
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Old 09-19-2012, 08:31 AM   #8 (permalink)
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My 98 Sporty had a CV carb I'd have this happen and cut the idle speed. Low jet could not be adjusted, screw was stripped. Can you drop your idle speed down any??
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Old 09-19-2012, 08:40 AM   #9 (permalink)
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Running about 1020 rpm on idle. Heard alot of scare stories about dropping idle too low. Engine damage and such. So, I don't think I want to go any lower.
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Old 09-19-2012, 08:46 AM   #10 (permalink)
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Quote:
Originally Posted by Fuzzy66 View Post
Running about 1020 rpm on idle. Heard alot of scare stories about dropping idle too low. Engine damage and such. So, I don't think I want to go any lower.
Time for an expert here but unless you've got EFI I don't understand why your idle is up that high. Just my .02
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