XS360 blowby?

[timhypo]

Let me start by apologizing if I need to do an intro before jumping in and making a post. Point me in the direction of the intro area and I'll be happy to. So, we got this xs360 for my wife, neat little bike - kick and electric start, parallel twin, nice and light. I did the usual setting of points, dissassembling/cleaning/checking for vacuum leaks on the carbs, verified that we're charging, replaced broken fusebox. I also rebuilt the petcock and cleaned/coated the gas tank. So, it idles pretty good most of the time, but not reliably and it sporadically loses power. Not at a certain RPM, but randomly at different RPMs as I rideit. I think the loss of power may be related to the inline filter I was running between the petcock and carbs - wanted to make sure I knew it if the tank was still spewing rust before I had to clean out a jet or worse. I'm removing that tonight as I've not seen a speck of rust come through since cleaning the tank.

Once I got it warmed up, though, it appears to be spitting some exhaust (I say exhaust, but it's really more like warm air) out the points cover. I removed the points cover and ran it with the points exposed and it REALLY seems to be coming from there. I know the exhaust manifold and head/jug connection are there, so I double-checked and that's really where it's coming from. I know the points sit on the end of the cam and there's a seal there that's undoubtedly blown, but why it's happening is my question. I guess this might be a normal amount of turbulence in the valve cover on an OHV motor (I usually mess with pre-60s american cars, so I'm a little inexperienced with OHCs other than my 240z), but it seems like a lot. What could cause this? Timing? I actually (winces) haven't checked the timing or run a compression check as this bike was supposedly a runner when parked and I wanted to make sure it starts, stops, and shifts before I invest much in it. Anything else this could be? Just a normal amount of turbulence in an OHC valve cover?

[drewpy]

Tim,

I'd check that the breather hose (rear of engine, behind the starter cover) is not kinked or blocked, this releases the pressure from the gearbox/crank area and the cam chain shaft (which goes into the rocker box).

If that is clear then you will need to do a pressure test as this would be the easiest thing to do next.

let us know how you get on

drewps

[JimR]

Let me start by apologizing if I need to do an intro before jumping in and making a post. Point me in the direction of the intro area and I'll be happy to. So, we got this xs360 for my wife, neat little bike - kick and electric start, parallel twin, nice and light. I did the usual setting of points, dissassembling/cleaning/checking for vacuum leaks on the carbs, verified that we're charging, replaced broken fusebox. I also rebuilt the petcock and cleaned/coated the gas tank. So, it idles pretty good most of the time, but not reliably and it sporadically loses power. Not at a certain RPM, but randomly at different RPMs as I rideit. I think the loss of power may be related to the inline filter I was running between the petcock and carbs - wanted to make sure I knew it if the tank was still spewing rust before I had to clean out a jet or worse. I'm removing that tonight as I've not seen a speck of rust come through since cleaning the tank.

Once I got it warmed up, though, it appears to be spitting some exhaust (I say exhaust, but it's really more like warm air) out the points cover. I removed the points cover and ran it with the points exposed and it REALLY seems to be coming from there. I know the exhaust manifold and head/jug connection are there, so I double-checked and that's really where it's coming from. I know the points sit on the end of the cam and there's a seal there that's undoubtedly blown, but why it's happening is my question. I guess this might be a normal amount of turbulence in the valve cover on an OHV motor (I usually mess with pre-60s american cars, so I'm a little inexperienced with OHCs other than my 240z), but it seems like a lot. What could cause this? Timing? I actually (winces) haven't checked the timing or run a compression check as this bike was supposedly a runner when parked and I wanted to make sure it starts, stops, and shifts before I invest much in it. Anything else this could be? Just a normal amount of turbulence in an OHC valve cover?

Tim,

I would guess just setting up the dwell, timing & carbs would put it right. The warm air coming out of the points cover does indicate problems with the cylinder head but tbh it is difficult to work out where thats comming from unless u know that for sure ! Dont forget the XS is OHC & not OHV !!!

Regards Jim

[timhypo]

Thanks, guys. I checked the breather tube that runs to the airbox from the starter area and it was loose. Tightening it up seemed to cure the blowby issue. The fuel filter also proved to be a bottleneck when it's replacement led to much more consistent idle and less weird power losses (amazing what happens when the bowls stay filled). It was still idling high after all this and wouldn't rev over 8000 and I even searched for vacuum leaks with the wd40 method before hooking up a vacuum gauge and got 13 pounds but fairly steady for a twin. 13 pounds!?!? It turns out the previous owner, who knows little about bikes, turned the idle way up, probably to try to compensate for the dirty carbs, poorly set points, and petcock feeding more fuel than air from the rusty tank. This thing runs like a raped ape, now. Or, at least compared to my sportster, but american twins are pretty slow.

The only thing left at this point is to fix the front brakes. They locked up one day and stayed locked up even after I removed the line from the caliper. I ended up pulling the caliper off the disc and plan to rebuild it now that the bike runs nice.

As for the OHC / OHV thing - I'm used to talking about the merits of flatheads verses early ohv motors. Forgive me.