First time this has happened in 45 yrs.

[mjpchief]

Had the bike out the other day for a ride and had just left the coffee shop. When I pulled up to a stop sign the left bank backfired and the bike was only running on one cyl. I managed to get it home on one cyl. and pulled the plugs out to check compression. It was good and when I looked at the plugs the left plug was dry. Decided that something had happened to the carb and when I went to pull the left carb off I discovered that it had been blown out of the carb mount. Never had seen this before. Put it back in the mount and bike ran fine. A couple of days later it happened again. Reinstalled the carb and bike runs fine. The mounts are aftermarket from MikesXS.

In the past the bike has popped back through the carb and died but started right back up. Still running point ignition with a recent tune up (150 miles).

 

[Team Junk]

Time to replace the rubber spigots.

 

[member28833]

Well, I did have a set of linked BS38's fall out of the manifolds one time.
Of course I can't blame the design. I was infact lost in a neighboring town and just a bit late which led to excess speed over a series of speed bumps.
Anyway, I learned that if you thoroughly clean any slick petrol film out of the manifolds and install the carbs with just a little soapy water and have clamps in good condition there should be no reaccurance.
Even if you have eliminated the airbox of course.
-R

 

[5twins]

I've had that happen a couple times. It seems most likely to happen when the bike is in that "gray" area between cold and warmed up. What can also cause the misfire is the timing being off a little bit. You said you just recently did a tune-up. You may want to check the timing again. Maybe it's off a little.

 

[mjpchief]

Will double check timing. Didn't discover the carb being blown out until I went to take the fuel line off of the left carb and was wondering why the fuel line clamp was so close to the side cover. Felt like an idiot when I finally figured out why.

 

[grizld1]

Carbs popping out of the boot is very often caused by a defective advance governor ("automatic timing unit"). When the tips of the bobweights wear the advance curve stretches, so that setting timing in a safe range at full advance retards the spark too far at idle, and setting idle timing correctly puts advanced timing in the piston holing range. If that turns out to the problem there are several good ways to correct the advance curve, and a quick search will take you to them. Don't try to correct the curve by bending or beating the limiting tabs on the advance rotor, though. You may not see them, but tiny cracks will result, and sooner or later (sometimes much sooner), vibration will do its work. Result: you'll find a loose tab in the bottom of the housing after the engine dies.