Air blowing from oil fill location

[Bdubbs]

I have air blowing out of the oil fill location when the engine is running (and the oil cap is removed) and I have low power when bike is under a load. the motorcycle runs fine though. I have not checked the compression yet but does anyone know what causes this or is the air coming out unrelated to the low power issue?

 

[gggGary]

The crankcase of any 360 twin is a powerful air pump. Yamaha changed the crankcase vent system about yearly, never with "complete" success. Sooo.....
Yes the oil fill will make a heck of a mess in short order if the cap is off and that's normal. Now get thyself a compression tester.
PS last summer I had the oil cap sitting off while working on an XS reached over and hit the starter while on the LH side setting carbs by the time I came around to the RH the shop was a mess.

 

[Jim]

It's a 360 twin. Both pistons go down at the same time. Air's gotta go somewhere... normally the breather. Leaving the dipstick out is just a big invite for the air. Probably not related to the power loss. Could be compression, fuel, ignition... dragging brakes .. Time to start eliminating. A little history on how it's been running would help.

 

[Bdubbs]

My cousin was the previous owner. was running fine. his son rode it last, then when he went to ride it it wouldn't move. sat for a year. i bought it and realized that it threw the chain. installed new clutch plates as well. bike will ride down the street but bogs down under the weight of a rider so not a ceased brake issue. i will check compression. i have spark at both plugs, so i believe coils and plugs are ok. if it is compression would it be the gaskets at the cylinder, rings, or both? any other thought will be appreciated. thanks for the input.

 

[Jim]

We're getting there... but ya still gotta give us more info. You say bogs down. That's pretty subjective. Answer these questions;
1. Does it start easily or does it not want to start? Does it keep dying?
2. Is the idle smooth or does it sound like it's only running on one cylinder?
3. Is there any misfiring, backfiring... unusual farts of any kind? If so, when?
4. When you say "bogs" do you mean it just dies or just won't accelerate?
The more info you give, the easier it'll be to diagnose. Sitting for a year.... I'd suspect fuel and carbs first... but give us more info.
Btw... welcome to the forum.

 

[Bdubbs]

1. start easily and runs great even when giving it throttle. (both exhaust pipes are blowing exhaust with equal pressure)
2. sounds smooth
3. none
4. so under normal conditions you can hear the engine work a bit harder under load when you accelerate the throttle until the bike starts moving (more so than in neutral).
in my case the engine works harder almost like it would stall out but it doesn't stall. (I weigh 200lbs if you put a 300lbs guy on there it probably would stall) if i have to, i can take it for a spin and post a link here to my FB page or email it to you.

 

[Jim]

If you upload a video to Youtube, you can link it up here. I don't do Facebook. From what you describe (sounds and runs great), plus the fact that you changed the clutch plates, there's a possibility something is binding up in the tranny.

 

[Jim]

My cousin was the previous owner. was running fine. his son rode it last, then when he went to ride it it wouldn't move. sat for a year. i bought it and realized that it threw the chain.

Just noticed that.... Did you pull the front sprocket and inspect for damage? Cracked cases... bent output shaft.... anything out of the ordinary?

 

[gggGary]

He's looking for a mechanic, Prolly a good thing.

 

[5twins]

If the engine is revving up OK but the bike just isn't moving as it should, it may have something to do with the clutch work you did. Maybe you didn't assemble the clutch pack correctly and the clutch is slipping. There's also an alignment dot on the basket that has to show through a little hole in the pressure plate. Get that on there wrong and the clutch won't work right.

 

[gggGary]

Threw chain, wonder if the rear wheel bearings were changed previous to that.... We know what comes next.

 

[MaxPete]

Hmmmmm....I wonder if the choke (enricher) is stuck on or the advance mechanism is seized.

 

[Jim]

or the advance mechanism is seized.

That was one of my first thoughts also.... but if it ran good and supposedly still does, but won't go anywhere under load.... And it threw a chain.... and the clutch was taken apart.... well, just a little too coincidental.... doncha think?

 

[MaxPete]

Yup....sounds like someone has been in there “experimenting”.

 

[Bdubbs]

Just noticed that.... Did you pull the front sprocket and inspect for damage? Cracked cases... bent output shaft.... anything out of the ordinary?

sprocket is good, no cracks in case.

 

[Bdubbs]

That was one of my first thoughts also.... but if it ran good and supposedly still does, but won't go anywhere under load.... And it threw a chain.... and the clutch was taken apart.... well, just a little too coincidental.... doncha think?

clutch is installed correctly. lined up dots. kept screws/bolts in the same location. it only threw the chain because the nut came loos. no sprocket damage.

 

[Bdubbs]

Threw chain, wonder if the rear wheel bearings were changed previous to that.... We know what comes next.

what comes next shell bearings were not changed and wheel spins freely.

 

[Bdubbs]

thanks for all the suggestions. looking more and more like a compression issue. ill get a tester and see what it shows.

 

[Jim]

Did you remove the clutch basket? Or just the disks?

 

[Jim]

thanks for all the suggestions. looking more and more like a compression issue. ill get a tester and see what it shows.

Well, it certainly don't hurt to check compression. But speaking from experience, I've had bikes with rings worn so bad you could kick start 'em with your hand.... and I could still manage to coax 'em up to highway speed.