We are all still looking for the first Raptor based oil-in-sump episode as that will be the first true "non-aggravated by vac petcock up down fuel levels" float needle/seat failure.

We are still looking for that first one so we can understand it.

Every 3-4 months we see a clear example of the other kind, newbies bring it to us as a " carburetor problem".

Oh arrg, my parrot done pooped on me durn jacket again .....

Silly bird,  I ought to introduce you to yer cousin the crow whut lives in the freezer ....   mebbe I'll let you visit with him fer a while if you crap on me jacket again.

               

Verslagen is saying his own personal human errors & hose clamp laziness are causing his occasional stumbling, not his petcork -- so his cylinder walls and piston ring zone are safe from any little lean events.  

Well, his clampless vac hoses won't hold suck good enough on his freshly rebuilt vac petcork and his petcork/engine combo ARE stumbling, so's unless I am missing something, mebbe his float levels are going down on occasion and mebbe he does lean out a bit.   So, mebbe he is a wee bit at bit at risk to developing sudden onset oil consumption.

And Verslagen is honest enough to tell us when his rebuilt engine starts using any oil out of the ordinary.    He won't like it, but he would tell us.   He would start out with a statement how it was normal at this mileage, etc etc and we would all stomp our mugs on the bar as he finished each sentence and say "Arrgh!" at the end of each one of his proclamations.


   



(Me wee little soaring carnivore bird ain't got no vac hose for me to be failing to put a hose clamp upon, sos I canna be a telling him I have the same issue to deal wid.    Mine jest runs, no stumbling to it )

Now now don't be a calling the loyal crew of HMS Ye Old Stock Vac Petcock no scurvy names there me maty .... some of them crew with us on other issues so they can't actually be no simples nor stupids -- that ain't kerrect at all.

We don't even really disagree on the actual facts -- it be what actually happens inside that mysterious vac petcork when it blatts about is whut we disagree on mostly.

We don't disagree that it expels gas on occasion, we jest can't agree as to whether it is a flatulence or a belch .....

And although the wimmen folk are vocal and surely don't like it very much, we men cannot come to a consensus how really truly serious them little couch & chair circular brownish stains really really are.

Running at highway speed, your vac petcock fuel delivery rate goes lower because the intake tract vacuum level goes down a bit on our engines at full throttle -- so a little less gas (relatively) is flowing into the bowl.  The bowl level starts to go down a bit, so the fuel height pressure to the main and pilot jet goes down a little bit as well.

So, a little less gasoline hits the same air volume going past the butterfly in the venturi so your engine power goes down a little bit.  So, you crank a little more butterfly open to try to keep up the same speed.  So,  your fuel delivery is down, your float level is decreasing and you are turning open the butterfly in the venturi more to get a little bit more "go" out of the engine.   It is a feedback cycle, resulting in lean conditions in the combustion process in the cylinder.

This increasing "lean out feeback cycle" continues until you can't get enough gasoline to keep your speed up at all, and you feel this and call it "an occasional mild stumble".   You may think you need to get some gas and you might stop and get some and this may actually help as more gas in the tank means more vertical pressure at the petcock and a little more gasoline will flow at a given vacuum level.  

But, say you are on the way to work and you jest keep on getting down the road.

Lean combustion conditions raises the piston crown temps, higher crown temps expand the piston crown a wee bit more than the cold measured .005-.0055" ring area running clearance can accommodate and the hotter than normal piston ring area begins to run into a mild interference condition with the cylinder wall.

Now, this is a mild case of early chronic lean out -- you won't melt a hole in the top of the piston for a little while yet nor will you pop a valve just yet and your ring grooves widths aren't going to shrink or gall just yet.

Now, how good is your oil?   Maybe you won't seize, perhaps you will just get some intermittent friction piston braking when the oil film starts to break down jest a little tiny bit.   Heck, feels just like another little stumble to me, crank the biatch open some more and let's go -- I gotta get to work.

You keep on running lean conically because your vac petcock isn't keeping your bowl full and eventually mild galling starts on your piston, generally right up on the front side of the wrist pin support running up towards the crown up past the ring grooves.  The rings begin to get pinched or impeded by the displaced metal, and low and behold you start using more oil.   You don't notice it for a few days or weeks as you are used to your bike not using any oil, so when you do notice it,  to you well you just suddenly started using oil --- "sudden onset oil consumption".


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I can tell you exactly when mine happened -- I was on the new 285 bypass around Charlotte getting ready to take the I-85 exit to go west on I-85 to hit 321 to go up to Toymaker's -- I was winging it at 85 mph keeping up with beltway traffic and getting a mild stumble so I thought I was needing some gas, I flipped to reserve and kept on getting it as I knew eventually putting it in reserve was going to get me some gas.   I stumbled/mini seized my way down to 65 mph before I hit the exit, then I rode (stumbling) until I got to the next exit with a gas station.

I could not put 2 gallons of gas in the tank, but I didn't know what that meant back then.   Nobody had ID'd the vac petcock as a major pain in the butt back at that point in time, but lots of us sure had odd carb issues we chased with jets and carb tear downs, oh lordy yes ....

But I noticed I needed to top up my oil at Toymakers.

verslagen1 wrote on 08/19/11 at 14:05:37: