blowing off the vacuum cap

[Fuller56]

Again this week Three ( ZG1000 #3 for me) blew off his vacuum cap for carb #3.  He does this about once a year.  The previous 2 did this occasionally but not as frequently.  Any of you guys seen this before.  Not a big deal as I now carry a spare, just curious.  Stock state of tune except for SISF's cam sprocket timing mod.  He runs great and gets high 40's fuel mileage and closing in on 60k miles.

[turbojoe78]

Is it backfiring when it's doing it?

Stock cap?

Some of the aftermarket caps don't fit all that well, you may want to get the stock one, more money but better fit.

[Jim __]

What were you doing when it popped off?  Accelerating, slowing down, cruising, etc.  I've never had one pop off but I sure appreciate the tip to carry a spare.

[Steve in Sunny Fla]

needs a valve adjustment. this is the same phenomenon I show on the "this is why we need to adjust valves" video. Steve

[Fuller56]

More details.  I have done the valves since the initial post, one #3 intake valve was .001" tight and was adjusted.  Conditions for the event.  Nothing unusual as I had just left one store and when I got about a mile up the road to the next it was running rough and idling poorly.  No back fire, no popping, just tired of wearing that cap I guess.  I did find it lying on the engine case when cleaning up.  This isn't really a big issue, I was just wondering if others had seen it.

[T Cro ®]

I've always used a piece of hose with a properly sized short screw in place of caps as I've never cared for their quality or fit....