Blowing oil out vent tube.....BAD! By mapbike (Read 10,038 times)

[mapbike]

Well, as you can see by the subject title I have an issue of blowing oil when I run at WOT down the highway.

Now I made some changes to the PCV tube by detaching it from the air filter box that is under the seat and running a 2 foot piece of 1/4" fuel line from the valve cover vent nipple and then I routed the hose toward the back of the scooter under the side panel and then it points down toward the CVT cover.

I just came back from about a 5-6 mile ride which was mainly on the highway where I was running 50-55mph 6500-6700RPM most of the time, before I got back I slowed down and looked back at the CVT cover and it was completely covered with oil that has been spraying out of the vent tube, the reason I disconnected the tube from the air box in the first place was because the slight amount of oil that was going in the box was just saturating my air filter with oil over time and I wanted to eliminate that problem by venting the presssure and the oil out of the box.

Obviously I have made my problem worse by replumbing that PCV tube....., I have included a pic of a possible fix I'm considering from scrappydodscooters.com, I'm wondering if this part will actually solve the excessive PCV problem I'm having.

My engine only has 1840 miles on it and it never put out very much oil in the air box at one time or anything like that, but I just wanted to get that heat and oil away from my fuel/air intake but I can se that just a wide open yube hooked to that vent isnt gonna work at all unless I just putt around and I cant do that when I ride 16 miles on the main highway to work on this thing.

My scoot is a Roketa MC74-150cc, and the engine runs very good, just rejetted the carb today to a 115 main jet, and made a couple more adjustments as well, but when I ran than open tube for the PCV I messed up and need a pros advise on the best way to resolve this issue without breaking the bank.....

Thanks in advance fella's

Peace

Attachments:

[ce]

You should only have about 15 ounces of oil in there, check with the dipstick level inserted and not screwed in on the centerstand. Excess oil will blow out the vent.

Check to valves to make sure they are set to .004 intake and .005 exhaust.

Replace the airbox and connect the vent tube to it.

[Cruiser]

Hi mapbike. Some blow by is normal, but your miles are not that high so it should be within normal limits. Hanging the vent tube down and open is a bad idea. Here's an article on oil catch devices that our members have used.

www.scooterdoc.proboards.com/index.cgi?board=techtips&action=display&thread=2441

[mapbike]

Yeah I know some blow by is normal but I knew something was pretty wrong when I lost about 1/2 cup of oil in a 5-6 mile trip, I have since put that PCV line back on the air box for the time being and then I took a 10+ mile round trip ride on the highway and things seem to be good now.

I have been planning on making a catch can for a while now but just haven't had the time but it will be done asap.

now I need to get my carb adjusted a bit better and get my clutch worked out, I put a ( Yellow ) 1500 RPM main spring in my clutch today and a set of 10g roller in the variator and that was a big joke......5000RPM at 30mph......! & only 48-50mph Top speed.. eek.! so then I put some 13g sliders in the variator and it lowred the revs at lower speed some but my top speed was still about 5 mph slower than it was with those same sliders and the 1000RPM main spring in the clutch, so I then put another set of rollers I had modified in th evariator 3 @ 17g & 3 @ 14g and now the RPM's are down but the top end is still off and it is a dog taking off.......I may put the 1000RPM spring back in and order some 12g sliders and see what that does to it.

I might consider going with a higher set of gears like maybe an 18T pinion set up, then maybe could run the lighter rollers or sliders and not loose my top end speed......??


Peace

Not sure I'm to impressed with that 1500RPM main spring in my scoot

Jul 3, 2011 18:19:48 GMT -6 Cruiser said:

Hi mapbike. Some blow by is normal, but your miles are not that high so it should be within normal limits. Hanging the vent tube down and open is a bad idea. Here's an article on oil catch devices that our members have used.

www.scooterdoc.proboards.com/index.cgi?board=techtips&action=display&thread=2441

[sprocket]

I never change the contra spring..waste of time and money.. the stock one is fine for 95% of riders..

You keep taking about the PVC tube.. do you mean the valve cover vent tube?? There is a PVC device on some engines, it is a silver 'U' type tube. Most people simply block these off . You can buy or make a small block-off from aluminum...

The Vent tube comes off the top of the valve cover from a 90 degree elbow... it should never be blocked or you could have gasket and seal problems...

Just stick the vent hose in a catch can or stick a fuel filter on the end and zip tie it high on the frame so the oil drains back into the cover... The filter should be checked every month or so, to be certain it passes air freely...

If you have excessive oil you may have too much oil in the engine.. check your level. You should use only 750 ml in an oil change...

[dyoung1167]

my vent line to air box is it's own little section. open on top to the filter but has a wall to separate it from the rest of the bottom of the box. i just put some foam in it so it doesn't blow the oil up into the air box and it can drain back in to the engine. easiest mod ever.

[sprocket]

How does it drain back into the engine?... it can't from the air box...

[mapbike]

The tube you are calling the vent tube is just another word that refers to PCV tube ( positive crankcase ventilation ) that is what PCV stands for, the steel tube you are refering to is the " emission control stuff they put on these to make them legal for some states from what I gather.

My air filter box sit directly over the engine so oil will drain back into the engine if it is blown up into the small chamber where the PCV/vent tube is attached.

I will post pics of the catch can I make for mine once I get it done, I plan to make it so any oil that gets in it will drain back into the engine and the pressure itself will be vented through a filter also.


Thanks for all the input on this everyone.....

Peace

Jul 4, 2011 11:04:44 GMT -6 sprocket said:

I never change the contra spring..waste of time and money.. the stock one is fine for 95% of riders..

You keep taking about the PVC tube.. do you mean the valve cover vent tube?? There is a PVC device on some engines, it is a silver 'U' type tube. Most people simply block these off . You can buy or make a small block-off from aluminum...

The Vent tube comes off the top of the valve cover from a 90 degree elbow... it should never be blocked or you could have gasket and seal problems...

Just stick the vent hose in a catch can or stick a fuel filter on the end and zip tie it high on the frame so the oil drains back into the cover... The filter should be checked every month or so, to be certain it passes air freely...

If you have excessive oil you may have too much oil in the engine.. check your level. You should use only 750 ml in an oil change...

[sprocket]

If it is blowing that much oil you have another issue.. have you overfilled the oil level?

There should just be oil vapor coming from the PVC hose.. any more and there is a problem...

[mapbike]

As long as the vent line is attached to the air box vapor is all I loose but it was when I added the extra long hose that ran 2/3 of the way to the rear of my scoot that I started blowing large amounts of oil, now that that line is reconnected to air box all seems to be fine, not sure why adding the extra lond length of hose caused the problem but some how it did.

engine was not over full of oil either, level was where it should be...shrug!

? not sure what caused that issue at all, I've been unprofessionally building and performance tuning small 4 smoker engines for 32 years and I've never seen this happen or know why, some sort of a vacuum must have been created some how in that hose for that much oil to get into it, the 7-8" line that runs to the air box stays basically dry other than just a film of oil that collects from the crankcase venting pressure.

Oh well, I'll know not to run that hose like that again on this GY6.

Peace

Jul 8, 2011 12:08:27 GMT -6 sprocket said:

If it is blowing that much oil you have another issue.. have you overfilled the oil level?

There should just be oil vapor coming from the PVC hose.. any more and there is a problem...

[sprocket]

Huh.. really weird. I wonder if the long hose caused a back pressure and prevented the v-cover from venting...

It is suppose to puff, puff, puff out of that vent perhaps with the long hose the first 'puff' hadn't cleared the hose when the second and third puffs one came along...

I just have mine about 12" long and I stick a fuel filter on the end and zip tie it to the frame up high so any oil in it runs back into the engine...I change the filter every 3-4 oil changes...

[mapbike]

Yeah you make a good point about the pressure possible multiplying or something, it is like you said weird, I even talked to my Dad this evening about it and he said that he couldn't figure it out either, I road the scoot WOT most of 20 miles today and not a single bit of oil loss with the short tube hooked back to the air box........Wow this has me scratching my head wondering what the heck would make adding an extra 18-20" of hose cause such a vacuum are whatever it is that seems to draw the oil out like it does.

Oh well, I'll just make me a catch can or I may do what you did and just use a piece of tubing about stock length and put a good fuel filter on it to catch the oil vapor as it condenses back to liquid.

I wanted to vent mine farther back and away from things because I live in the country and ride on extremely dusty dirt roads and I do mean extrememely dusty Caliche roads around here, stuff is as fine or finer than talk powder and gets in and on everything, this is a real challenge for one of these scoots because everything stays covered in dust all the time unless it is washed off or blown off constantly, so I have to make sure everything is fixed so I can keep the dust out as good as possibleand still get adequate air flow to and around the engine.

Thanks for the tip and convesation on this trouble I had I really appreciate any and all help and hope I can offer the same from time to time.

Peace

Jul 8, 2011 17:34:26 GMT -6 sprocket said:

Huh.. really weird. I wonder if the long hose caused a back pressure and prevented the v-cover from venting...

It is suppose to puff, puff, puff out of that vent perhaps with the long hose the first 'puff' hadn't cleared the hose when the second and third puffs one came along...

I just have mine about 12" long and I stock a fuel filter on the end and zip tie it to the frame up high so any oil in it runs back into the engine...I change the filter every 3-4 oil changes...

[dyoung1167]

sprocket, it simply runs back down the line. maybe not so much while running but after it sits yes. the foam stops it from blowing over the top and gravity does the rest. course my air filter is under the seat and over the engine. wouldn't work on the ones where the air box is over the cvt.