1991 Electra Glide Evo smoking at idle
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3rd Gear
Joined: May 2026
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From: Denmark
Thanks for bringing that up, I was not aware of that. I will check it as soon as I have the opportunity.
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3rd Gear
Joined: May 2026
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From: Denmark
Welcome to the HDFORUM.
Put a dual range vacuum/pressure gage on that vent hose at idle briefly. See any bounce towards zero pressure
If you don't have a gage, you may still be able to fill a slight very brief vacuum especially if your geared rotary breather valve or it's bore is worn.
Fill or see any vacuum? That why the later Harley when they did away with the spinning geared breather vent valve in the cam chest and simplified it by put the one way poppet valves in the rocker boxes needed those one way out poppet valves.
That's why modified vents to the outside have a filter.
The later design poppet valves are one way out. Modifications from them to the outside probably still need a filter since the rubber valve ones may eventually fail. As designed, the hose from then is in the filtered air filter box area.
Even if you had a more modern head vent poppet valves, they shouldn't cause too much oil vapor in vent line unless engine has excess blowby from wear.
Put a dual range vacuum/pressure gage on that vent hose at idle briefly. See any bounce towards zero pressure
If you don't have a gage, you may still be able to fill a slight very brief vacuum especially if your geared rotary breather valve or it's bore is worn.
Fill or see any vacuum? That why the later Harley when they did away with the spinning geared breather vent valve in the cam chest and simplified it by put the one way poppet valves in the rocker boxes needed those one way out poppet valves.
That's why modified vents to the outside have a filter.
The later design poppet valves are one way out. Modifications from them to the outside probably still need a filter since the rubber valve ones may eventually fail. As designed, the hose from then is in the filtered air filter box area.
Even if you had a more modern head vent poppet valves, they shouldn't cause too much oil vapor in vent line unless engine has excess blowby from wear.
Thanks for the detailed explanation. I understand the logic behind the vacuum and the breather gear now. I do not have a vacuum gauge at the moment, but I will try to see if I can feel any brief vacuum from the hose by hand. It makes sense why the filter is there if the system is sucking air back in. I will look into getting a gauge to do a proper test to see if the breather valve or the bore is worn. Thanks a lot.
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Joined: Mar 2010
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From: Honah Lee
Yes, that's learned. What he's doing here.
And he's eliminated some just talking.
My guess here now would be a warm engine compression test with the throttle held wide open.
And he's eliminated some just talking.
My guess here now would be a warm engine compression test with the throttle held wide open.
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Joined: Mar 2010
Posts: 38,419
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From: Honah Lee
Thanks for the detailed explanation. I understand the logic behind the vacuum and the breather gear now. I do not have a vacuum gauge at the moment, but I will try to see if I can feel any brief vacuum from the hose by hand. It makes sense why the filter is there if the system is sucking air back in. I will look into getting a gauge to do a proper test to see if the breather valve or the bore is worn. Thanks a lot.
None of that detail was ment for your smoke issue. Just the filter rational.
It's probably self cleaning.
??
.I don't think vent especially since it's not in airbox or your oil level is your smoke issue.
Does Denmark frown on a little smoke from 35 year old antique Harleys?
Last edited by Jackie Paper; Yesterday at 08:39 AM.
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3rd Gear
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From: Denmark
None of that detail was ment for your smoke issue. Just the filter rational.
It's probably self cleaning.??.
I don't think vent especially since it's not in airbox or your oil level is your smoke issue.
Does Denmark frown on a little smoke from 35 year old antique Harleys?
It's probably self cleaning.
??.I don't think vent especially since it's not in airbox or your oil level is your smoke issue.
Does Denmark frown on a little smoke from 35 year old antique Harleys?
No problem with a little smoke from an old lady in Denmark 😄
My concern is mostly about my own vanity; I just want the bike to run as clean as it looks.
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Joined: May 2008
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From: South Carolina
Pull the spark plugs, clean the threads and put a little anti seize on them, reinstall the plugs (you do this as a precaution because you will be removing the plugs from a hot cylinder head).
Get the tools ready for a compression check, then take the bike out for about 15 minutes.
Pull the plugs and do the compression check (remember, throttle butterfly wide open).
What are your numbers?
Get the tools ready for a compression check, then take the bike out for about 15 minutes.
Pull the plugs and do the compression check (remember, throttle butterfly wide open).
What are your numbers?
Last edited by Dan89FLSTC; Yesterday at 11:08 AM.
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3rd Gear
Joined: May 2026
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From: Denmark
Pull the spark plugs, clean the threads and put a little anti seize on them, reinstall the plugs (you do this as a precaution because you will be removing the plugs from a hot cylinder head).
Get the tools ready for a compression check, then take the bike out for about 15 minutes.
Pull the plugs and do the compression check (remember, throttle butterfly wide open).
What are your numbers?
Get the tools ready for a compression check, then take the bike out for about 15 minutes.
Pull the plugs and do the compression check (remember, throttle butterfly wide open).
What are your numbers?
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Joined: Apr 2011
Posts: 5,797
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From: SE Louisiana
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