Older Honda 70 blow-by / crank case breather question

[Blown 331]

I just picked up 2 more SL70s. :w00t: Anyway, right now I'm messing with a KO model which is a 1971. I got it running, does not smoke. On all my ATC70s and even a 1971 4 speed Trail 70 there is a crank case breather on top of the crank case behind where the air box mounts, A hose just slips on. On this SL, it does not have that. I got it running with the flywheel cover removed. Between the flywheel and front sprocket there is a hole with tons of oil mist (blow-by?) shooting out. It looks like is is supposed to be there. The bikes with the breather on top do not have this. So on this SL it has to be the crank case breather but there is no way to put a hose on it. Anyone ever seen anything like this and did the older 70s have a breather there? It's about an inch exactly infront of the neutral indicator. If you look on a newer 70 there is a lip that sticks up off the side case kind of in the shape of a "C". On this SL there is hole right in the middle. It's nothing broke or anything like that. The bike does not smoke a bit so maybe the oil ring is ok but the compression rings are not? It has no power and will barely run in the lower RPMs but once you wind it up it does ok. I even had it in 4th gear no problem on the road. Thoughts?

[Vealmonkey]

Some people have vented the cases by modding thie dipsticks drilling into the part next to the handle and adding a small threaded nipple there and running a rubber or nylon vent line there. Also a vent line tapped into the upper tappet adjuster acces hole can also help with some venting issues there. Check for compression and make sure your clutch is properly adjusted. Low compression or clutch slipping is more apparant in the lower gears, than the higher gears. Check your rear chain and your wheel bearings as these can put alot of drag on engine that only put out around 7 horsepower. Of course you have checked for proper timing and tappet adjustment made sure your points are properly adjusted and filed down nice and flat as these things can also affect performance. I know you are pretty mechanically savvy, but it doesn't hurt to double check. I can't believe you haven't posted pictures? I hope to get my xl70 engine running in my suspension atc70 and was thinking about picking up one of those 88cc kits and bolting that on. Best of luck with your 70s. Pictures please.

[Blown 331]

Some people have vented the cases by modding thie dipsticks drilling into the part next to the handle and adding a small threaded nipple there and running a rubber or nylon vent line there. Also a vent line tapped into the upper tappet adjuster acces hole can also help with some venting issues there. Check for compression and make sure your clutch is properly adjusted. Low compression or clutch slipping is more apparant in the lower gears, than the higher gears. Check your rear chain and your wheel bearings as these can put alot of drag on engine that only put out around 7 horsepower. Of course you have checked for proper timing and tappet adjustment made sure your points are properly adjusted and filed down nice and flat as these things can also affect performance. I know you are pretty mechanically savvy, but it doesn't hurt to double check. I can't believe you haven't posted pictures? I hope to get my xl70 engine running in my suspension atc70 and was thinking about picking up one of those 88cc kits and bolting that on. Best of luck with your 70s. Pictures please.


Thanks for the suggestions. But yep, I went through all that trying to get it running. The intake valve was a little tight, after that it ran but the blow by is just crazy and the vent seems to be in a weird spot. Here are the best pics I have right now.
The red one is one of the I just got, it has the blow by issues. The blue one is in super nice condition, everything works, not beat up or abused. I don't have a pic handy of the 3rd. Its missing the seat and tank but it was only $50 and it kicks over just fine.
I'm considering the 88cc kit for the red one with blow by also but I think I'll try the 3rd one and see how it runs. I may swap engines or just swap the missing body parts over from this red one for now.
The red one does need a seat cover. I will make one. I made the cover on the blue one and look how great that turned out.

[atc500x]

I will try to check on my sl70 where is the crankcase vent and let you know....SL70 are very fast!

[Blown 331]

I will try to check on my sl70 where is the crankcase vent and let you know....SL70 are very fast!

Thanks and you're not kidding. They are really amazing. The hand clutch models have the advance built into the flywheel, auto clutches (inc ATC70) do not. I also have a CT70 4 speed & hand clutch (has advance) and not even that runs anything like the SL. My CT70s will do like 41-42mph with me on them and the SL will bury the 50mph speedo with ease.

[atc500x]

I get 52 mph with mine with stock sprocket,I plan to maybe use it on raod and I will get a smaller rear sprocket to help a little bit

[Blown 331]

I get 52 mph with mine with stock sprocket,I plan to maybe use it on raod and I will get a smaller rear sprocket to help a little bit

Wow that looks great! Whats the story on it? Looks like maybe an older tank?

[Blown 331]

I ordered some rings on Monday then pulled the top end on Tuesday. The middle ring was broken into like 20 pieces! Never seen anything like that before. Should run good with some new rings!