External vent setup
Club Member
Joined: Sep 2010
Posts: 15,420
Likes: 7,118
From: Beyond Fucital
Do they (The head bolts) exhaust or intake or both? Trying to remember what I did that the bike wouldn't run and could have blown a head gasket (but didn't).
Seasoned HDF Member
Joined: Jan 2006
Posts: 11,463
Likes: 2,990
From: Charleston, SC
Yes, the system breathes "out", exit. Doesn't allow air to suck back in (that's what the one way umbrella stops). If it did, think about how much dirt and junk would go directly into the heads, which would be bad...
A blocked breather will cause the engine to run hot and sluggish. Can sometimes make the engine eat all the engine oil pretty quickly too.
Last edited by lp; Oct 3, 2015 at 09:43 PM.
Cruiser
Joined: Oct 2014
Posts: 102
Likes: 5
From: Kaysville, Utah
The only thing I would change, is that I used a little black silicon to fill the void where the hoses used to run,to keep any dust from coming through the groove unfiltered into the intake. Also I put a little K&N filter where the hose ends just about bottom frame level. I may be a OCD, but that's my 2 cents.
In a perfect world the butterflies keep there from being any sucking on the hose...but the butterfly valves are not 100% effecient. There is a small amount of air that does suck back into the engine via the breather system...more at start up and shut down, than while running.
Running a filter at the end of the hose not only guards against the very small chance of anything getting back up into the engine, but the bigger benefit is that it will absorb the oil and other gunk, not leaving drips in the driveway or garage, and not spraying the underside of the bike with oil mist to attract a layer of dirt.
If you are running a filter at the end of the hose and getting oil dripping out of it, it is either-
A cheap filter (or more than 5000 miles since the filter was cleaned)
Too much oil or crankcase pressure
Too low of a viscosity of oil for the temps being ridden in
Worn or defective butterfly valves
Check out a complete selection of External Breather Kits HERE
Running a filter at the end of the hose not only guards against the very small chance of anything getting back up into the engine, but the bigger benefit is that it will absorb the oil and other gunk, not leaving drips in the driveway or garage, and not spraying the underside of the bike with oil mist to attract a layer of dirt.
If you are running a filter at the end of the hose and getting oil dripping out of it, it is either-
A cheap filter (or more than 5000 miles since the filter was cleaned)
Too much oil or crankcase pressure
Too low of a viscosity of oil for the temps being ridden in
Worn or defective butterfly valves
Check out a complete selection of External Breather Kits HERE
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1. Hot, oily, oxygen depleted air combined with gas does not produce as much power as cooler, oxygen rich air combined with gas.
2. Build up on pistons will reduce engine longevity, and will make your tune that worked great today, not work so good 5-10k miles down the road.
