49cc 142F HS Air Breather Blow Back Issue

[Milkedglass]

Greetings All--

I have a new HS engine with under 200 miles on it and I have had considerable "blow back" from the air breather hole since Day 1.

Blow back is a gas/oil mix and I typically collect about 3-4 oz from a 20mile ride. I was told it is normal by the guy who sold it to me but I'm just not buyin that anymore. I have a hose running into a container to collect it all so it's more of an annoyance than anything. The engine runs great with no power issues. I'm relucant to open it up and make any valve, etc adjustments but any thoughts/ideas are appreciated...

 

[Frankfort MB's]

My HT 2 stroke does this but I don't have any air filter. I also don't have a reed valve so this is my problem.
I don't know much about 4 stroke kits but I would think that the valves would be off. You would think there would be a power loss or be rough running

 

[HeadSmess]

how much freakin oil is in it? thats the first thing to suspect... over filled. they will spray it everywhere if they have too much oil!

if its dipstick fitted, it should touch the end of the stick, but shouldnt spill out the hole, when the engines level. pretty well much flush with the bottom of the filler is the standard amount.

could be the little separator valvey thing in the carb is defective, blocked, etc. the hose from the crankcase should be entering the rear of the airfilter. if its not hooked up, it will spray oil everywhere. just try taking the dipstick off of any motorbike when its running!

it sounds like it doesnt even HAVE a hose? 3-4 inch tube from breather to airfilter...

straight fuel, not premixed .

its always a good idea to check the valve clearance occasionally, its only a five minute job...

 

[Milkedglass]

I had a breather hose connected to the air filter but of course it dumped fuel/oil back in it. Gunked all up.

I don't have it over filled with oil, just the recommended height.

Maybe I'll just go ahead and figure out a valve check.

 

[Milkedglass]

Adjusted the valves to .004 ex and .003 in as both nuts were loose.

Corrected the problem it seems...but I somehow cross threaded the spark plug. Ahhh!!! Ordered a thread chaser and hoping for the best

 

[HeadSmess]

oh dear...

still got some options. helicoil. take it to a shop and if your lucky they wont charge you a fortune. buying a whole kit is a bit silly. ring around, find a good price.

could order the next size tap and use a different thread/shank plug thats still a match. i think the "D" is a 12mm, where the "C" it normally has, is a 10mm. just change the first letter when you order replacement plug. cant remember how much clearance is between the valves and plug hole, might not work... a "B" is definitely too fat!

do all the drilling while its at TDC while both valves are just cracked open and you could possibly just blow/flush it out, rather than have to tear it down to get the filings out... give it a thorough wash out so its clean with no sticky stuff before doing anything...then again, four strokes dont mind a little bit of stuff going through the cylinder... its mainly just getting fine bits in the ring grooves that cause problems.

or you can just crack it open, they arent that hard to do.

 

[Milkedglass]

Fixed the threads pretty easily and all is well in that sense. That was a relief...until...I realized the blow back issue is still ongoing!

It is definitely something with the valves not seating right or timing because there was gas all throughout the head area and the rocker nuts had loosened again from all that, even with loctite.

I have to open this thing up and fix?? Ahh!!! Thanks for any help

 

[HeadSmess]

gas shouldnt be able to GET IN to the rocker area...hows your oil look? is it getting diluted with petrol?

thats the thing with fourstrokes...the gas/air mix goes in the port and only into the cylinder...meaning theres an issue in there somewhere...

my suspicion is the valve stem seal is leaking. its the only real way you can get that sort of blowback... that or theres a hole/crack/flaw in the casting in the general area... bent valve? how are the valve shafts regards fit in their little holes? some wriggle is normal, like half a mm at most...1/64" if you must use imperial...

you got one weird issue, that at least is a definite.

shouldnt need to locktite the adjustors, so for them to be loosening off is peculiar... normal adjustment is to allow for wear in the valve seat... otherwise theyre basically set and forget.


ps, its nearly impossible to grind the valves on these things...

 

[Milkedglassede]

Thanks for the advice.

The thread chaser worked.. until I did another plug chop and it didn't anymore. Last few threads are the culprit so it wont tighten. Damn! Blew it.

I'll give your suggestion a try here and open it up while I'm at it to look at the valves. Or hopefully give to my buddy to do. My spirits are low and I'm frustrated with how much time I've had to spend on this bike. Cheers

 

[Milkedglass]

HeadSmess...

Man, why do I have the sick feeling that this isn't gonna be an easy/or even possible fix after opening it up? Ha! Fml

Yes indeed, my oil has been getting diluted with gas/petrol to varying extents and I change it constantly from the blow back loss anyway. It seemed to be getting better lately but I kinda doubt it now. Yikes. Would that mean an engine flaw or typical for this kinda thing or ? Guess there's only one way to find out but I'm bout ready to start over with this 142f