Dirty Throttlebody Butterflies

[SkooterG]

It's been discussed before in other threads on other subjects, but I wanted to start a separate thread for discussion of the root cause of dirty throttlebody butterflies.

Like those you see here:

Approximately 160k miles on those from my first 2004 FJR.

We have seen others report the same thing. DCarver and Radiohowie that I know of for sure. In the past I have also had a couple folks PM me about the same issue. One only had about 30k miles on his 05 iirc and had the dirty butterflies.

I have seen one person describe the build-up as 'carbon', but mine was an oily, gunky, residue. Not carbon.

Also recently, a forum member said his were much worse than my photos above and the engine had been babied. So some theorized that occasional or regular running of the engine hard would be beneficial to keeping the TB butterflies clean. After what happened to me two weeks ago I am not so sure.

Two weeks ago I ran my FJR REALLY hard for just under 24 hours. During daylight it spent a LOT of time at WFO throttle and max speed running near, at, or even above readline continuously. For the first time that I have ever noticed, it consumed oil. About 1/2 - 3/4 of a quart in about 2000 miles. Well a few days after returning I changed my air filter and in doing so saw something I have never seen in over 300,000 miles of FJR ownership - wet, oily spots inside the airbox.

This is close to what I usually see when replacing the air filter. These photos are off a friend's 2004 FJR that I serviced and is 'worse' than typical. But I usally see a fine layer of dirt/dust that got past the (OEM) filter.

Well, a few days ago, after running my poor FJR at the limit for extended periods there were 'spots' of oily moisture throughout the airbox. At the bottom, in the little valley there was more of it, though not 'pooled'. Unfortunately I didn't get any photos of that, but I did get a photo of the paper towels after cleaning the interior of the airbox. These were completely clean before.

Thick, dirty, oily residue type of gunk. 'Normally' there would just be some light brown or tan fine dust on the paper towel.

So my theory is that all that high rpm continuous running is doing something (pressure build up in the crankcase?) that causes oil from the crankcase to get into the airbox through the crankcase ventilation hose that goes from the crankcase to the airbox (unfiltered side). I am guessing it is in vapor form for the most part?

And so back to dirty throttlebody butterflies. My theory is that the root cause of those dirty butterflies is oil vapor coming from the crankcase through the airbox and then sticking to the butterflies which then attracts and builds up along with whatever dirt is allowed through by the air filter.

So in other words, perfectly normal for the design of the FJR's engine and not anything to really worry about.

Thoughts?

 

[NMRoadRunner]

I would agree, running that hard and high RPM has to build alot of case pressure and with the milage of the bike and high cylinder presures being produced, there has to be some oil being blown by the rings. And the crank has to be frothing it up quite a bit as well. In a hurry were you?

 

[Bungie]

Read up on valve timing. Specifically overlap. Theirs a brief period of time where both the exhaust and intake valves are both open simultaneously. Nearly all high-perf engines are designed this way (except those with variable valve timing). That guck you are seeing is essentially exhaust flow back through the intake, and, maybe a bit of PCV valve sputum.

Depending on the valve timing, this reversion can be a lot or not much at all.

Course, I could be a computer programmer and not an engine designer and not have a f'n clue too.

 

[A41Billy]

Read up on valve timing. Specifically overlap. Theirs a brief period of time where both the exhaust and intake valves are both open simultaneously. Nearly all high-perf engines are designed this way (except those with variable valve timing). That guck you are seeing is essentially exhaust flow back through the intake, and, maybe a bit of PCV valve sputum.

Depending on the valve timing, this reversion can be a lot or not much at all.

Course, I could be a computer programmer and not an engine designer and not have a f'n clue too.

How would this make it all the way back to the airbox?

 

[Greb]

assuming crank case ventilation is the cause, would running the crank case vent line to a stand-alone air filter bypassing the airbox be a good idea?

 

[dcarver]

Mine at about 60k?

and close to 150k

Old style smart bikes vented CC vapors via filter to atmosphere. Like my Harley does. And the air cleaner stays clean. When I stabbed the donor motor into KrZy8 I seriously wanted to vent CC to atmosphere but didn't have parts avail given the time frame.

Speaking of carbon.. 100k worth of running, 150k total

More pix here.

 

[Fred W]

Read up on valve timing. Specifically overlap. Theirs a brief period of time where both the exhaust and intake valves are both open simultaneously. Nearly all high-perf engines are designed this way (except those with variable valve timing). That guck you are seeing is essentially exhaust flow back through the intake, and, maybe a bit of PCV valve sputum.

Depending on the valve timing, this reversion can be a lot or not much at all.

Course, I could be a computer programmer and not an engine designer and not have a f'n clue too.

With valve overlap, which almost all modern engines employ, the exhaust shouldn't migrate backwards through the intake tract. That would be really bad for engine efficiency as the next intake gulp would then be diluted with spent exhaust. It could theoretically happen if, due to the cam grinds, the overlap was extreme, as in a cam designed for high rpm operation, and the engine was lugged at heavy loads and low rpms.

Somewhat counter-intuitively, the reason for the overlap is actually to allow the inertia of the already departing exhaust gas charge in the column of the exhaust pipe to assist in sucking the new intake charge into the combustion chamber immediately as the intake valve opens. It's similar to how an expansion chamber works with reflected gas pressure waves on a 2-smoke.

Looking closely at the photos Skooter has posted, it does look like the deposits are granular, as if it was dirt stuck to oil. I think that is as good a theory as any. Someone would have to make a closer examination of the deposits to figure out their physical make-up.

 

[wheatonFJR]

...Looking closely at the photos Skooter has posted, it does look like the deposits are granular, as if it was dirt stuck to oil. I think that is as good a theory as any. Someone would have to make a closer examination of the deposits to figure out their physical make-up.

Skooter,

Did you lick the deposit so you know what it tastes like?

 

[Bungie]

With valve overlap, which almost all modern engines employ, the exhaust doesn't migrate backwards through the intake tract. That would be really bad for engine efficiency as the next intake gulp would then be diluted with spent exhaust.

Exactly, I'm sure you've heard a big v8 with a radical rumpy cam. Do you know WHY they sound the way they do? Of course you do. You just described it yourself.

But once again, I'm a programmer monkey.

 

[Bustanut joker]

...Looking closely at the photos Skooter has posted, it does look like the deposits are granular, as if it was dirt stuck to oil. I think that is as good a theory as any. Someone would have to make a closer examination of the deposits to figure out their physical make-up.

Skooter,

Did you lick the deposit so you know what it tastes like?

You had to ask..

Now he's going to go out and do it, an while tasting, he'll open the butterfly and get his tongue pinched

I hope yer happy :lol:

 

[SkooterG]

Well, I think DCarver's photos support my theory. With all the dusty dirt road riding he does, his are worse because of more dust getting past the filter and building up on the TB butterflies.

 

[Auburn]

assuming crank case ventilation is the cause, would running the crank case vent line to a stand-alone air filter bypassing the airbox be a good idea?

Part of race preping a road race bike is to put the crankcase vent into a separate catch can that is then vented to atmosphere. Purpose is to catch any oil that may be pushed out the vent due to high crankcase pressures. (Note: you have to do this if the vent does not go into the airbox)

I think Skooter may be onto the root cause. If he is getting oil from his crankcase vent baack into his airbox, the oil vapor is mixing with the fine dust and plating out on the butterfiles and the rest is getting into the combustion chamber.

 

[wfooshee]

You could compare it to a car's crankcase ventilation but a car vents to the intake manifold, which is behind the throttle plate(s). We don't have an intake manifold, so behind the filter is the next best place. In front of the filter would basically vent to atmosphere, and that's no good.

Yes, it's oil from the crankcase. Steadily high RPM has very little to do with it, I think, although maybe it's worse with life mostly above 5 grand, I don't know.

 

[wheatonFJR]

You know...I'm really liking this serious technical discussion without someone saying "jes sayin and enuf said"...but can't we take a commercial break with some girlie photos?...with throttle bodies in the foreground of course.

 

[Bounce]

So in other words, perfectly normal for the design of the FJR's engine and not anything to really worry about.
Thoughts?

it was a long way around the block to get back to the start.

 

[RossKean]

So, find out what it is rather than speculate! If I had a reasonable size sample of the material, I could do some chemical analysis on the stuff. Find out what proportion is organic (fuel residue, oil and/or carbon) and what portion is inorganic - silica, clay, wear metals etc. A trace element profile would provide a definitive answer. I'm not planning on stripping mine down to the TB's anytime soon but if I ever go there, I will carefully scrape as much stuff off as I can and do a bit of lab work on it (would need at least a half gram). If anyone wants to do this and send it to me, I would be happy to provide the answer. Hopefully customs inspection at the border won't be an issue...

Ross

 

[Fred W]

While we wait for the girlie pictures, another observation worth speculating on is why the top half of the throttle plates are always so much cleaner than the lower half, as can be seen here:

 

[BkrK12]

While we wait for the girlie pictures, another observation worth speculating on is why the top half of the throttle plates are always so much cleaner than the lower half, as can be seen here:

Effects of air flow past the pivot rod?

 

[beemerdons]

...Looking closely at the photos Skooter has posted, it does look like the deposits are granular, as if it was dirt stuck to oil. I think that is as good a theory as any. Someone would have to make a closer examination of the deposits to figure out their physical make-up.

Skooter,

Did you lick the deposit so you know what it tastes like?

You had to ask..

Now he's going to go out and do it, an while tasting, he'll open the butterfly and get his tongue pinched

I hope yer happy :lol:

SkooterG, I think that Bustanut joker **** in your gas tank! I definitely know he did that to Don Carver's!