So I finally got around to doing a breather bypass on my 2019 FLHTP.

I did find oil coating the inside of the throttle body outside of the butterfly and I just wiped all that stuff off with a rag and cleaned it up.

I took it out for an 80 mi ride today, some back roads, some interstate. The bike seemed to run smoother than it did before.

With a head breather not dumping oil mist into the combustion chamber, would it really have that much difference?

Oil was never dripping out of the breather, but the intake track was coated visibly.

Or it could be just my imagination and me being happy to be back on the motorcycle again. It has been a couple of weeks due to rain and a bit of travel in the van.

 

I put a breather bypass on my 2020, just because my bike was using a lot of oil and I didn’t know where it was coming from or going.

Like yours, the butterfly valve was somewhat cruddy. This was with 12,000 on it, but the new breather was catching very little.
And it didn’t run any different as far as I could tell.

 

1. Bypass on mine. Would not run it any other way...

2. The bikes are designed for the oil. NOT saying its a good design but, designed never the less!

3. Your imagination.

IMHO...

 

You could be totally right about all or most of that but my observations are a little different.

Yes, the vent lines do get coated. Not sure about your design but most Harley's are plumbed so only the vent air is actually drawn into intake.



The collection of oil usually falls out and drips down. I had a 05 Yamaha that had a catch cup in the air box. On the outside of the air box was a short drain tube with a cap. It would fill up in 10K but that motor turned a lot of high RPM as geared compared to a Harley and it had carburetors.

Now if the front part of the throttle plate has oil on it, the vent gas is plumbed too close to the mouth of the intake.

Now if there is a film only behind front of throttle plate that is not vent oil. That is the fall out from ever time you shut off the motor from the charge left in the intake from the injectors. It's the crud left from evaporated gasoline. (I believe but know for sure except in what I have seen)

The throttle by electric motor control helped somewhat with this by keeping the throttle open slightly if you throttle back quickly creating a richer mixture. The older position cable controlled butterfly system really do that and why EPA forced throttle by electric wire in cars.

Not just reducing it after you turn it off but coming up to a stop light. Now they have gone even further by taking the injectors out of the intake all together. (Which has created more problems then it fixed at first).

Be interesting to see real case tests in 6 months what's behind butterfly. Was or is it engine oil or from the injectors.

 

if it was dumping massive amounts of oil into the intake tract, it's possible. But, I'd say it's the placebo effect...

 

I had the same issue when I bought my new to me Fat Bob. The crankcase was overfilled causing more than normal BB mist and my TB was streaked with the Sh_t. Sprayed it out with carb/TB cleaner and bypassed the mist to atmosphere. I also am running 5ozs of SeaFoam for a couple tanks to clean out what I can't get to. I can't buy the premise the jetting/fuel mixture was designed for all that goop in the equation. As far as it running different, I just noticed the rear cylinder frying the right thigh more than before is all but then I also replaced a badly worn exhaust header with a new set which shouldn't affect anything.

 

I'll look at it in a few days when I've run a few hundred miles.

But the intake, just ahead of the butterfly, was covered in oil. A beautiful light covering of oil. It shouldn't reappear now as I've rerouted the head breathers outside of the intake.

 

I had heard of all the issues with the oil breather system on the M8’s. After a lot of research I am of the opinion that I don’t want anything but air to be sucked through my intake! After a couple of revisions I have completed my final catch can assembly. So far so good!

 

What did you do to the passages in the backplate that, in stock design, let oil/moisture and hot air from the engine get sucked into the intake?

 

Did you plug these holes? If not, your hoses aren't doing much.