Carb hissing

[Michael xs650]

Just installed pamco ignition / cleaned carbs / installed new fuel line and adjusted floats on my 1975 xs650. I opened my petcocks and found my fuel line wasn't filling up all the way and leaking a bit, also had a little bit of fuel coming from the jet needle hole on the left carb. So I tightend up the clamp on the fuel line and turned the ignition switch on. Once I saw that the lights were turning on with the ignition switch on I turned it off and a loud Hiss came from my carburetor. I don't get why this would happen without giving it a kick start... Anyone have any ideas ?

 

[jayel]

well if the piston on that side was on compression but intake valve wasn't compleatly sealed you would hear the compression bleeding off thru the carb

 

[pamcopete]

Michael,

If the transistor is on when you turn off the ignition when the engine is not running and one of the intake valves is open, then a spark will be created and ignite the mixture in the cylinder, blowing back through the carb. If one of the exhaust valves was open, then you would hear a poof in the exhaust.

This is the same as points if one set of points just happens to be closed when you turn off the ignition with the engine not running.

 

[1974jh5]

Pamcopete is exactly correct. Old Ford Duraspark ignitions would do the same thing, if you turned the switch on but didn't start the engine and then turned it back off, sometimes you'd hear a 'pook' noise in the exhaust or the intake. That was because it backfired for the same reason.

 

[Michael xs650]

So its perfectly normal ?

 

[gggGary]

Or normally perfect. You are good so far but sounds like you still have carb issues, which is also normal.

 

[5twins]

I had points, now a Pamco, and don't ever recall my carbs hissing. Yes, carb issues still, lol. On '75 carbs, there are a couple vent hoses and overflow tubes that should vent to atmosphere, not be connected together. Many make the mistake of connecting them to each other. That might give those carbs a hissy fit, lol.

 

[XSLeo]

My Harley does the woosh thing same as the XS with the Pamco.
From what you describe thats whats happening. If the carbs were hissing when running then I might think air leaks.
On your 75 the tail light and dash lights light with the key on, the headlight has an on/off switch. Turn the headlight switch off to start the bike, then turn it back on to ride.
Leo

 

[Michael xs650]

Thanks for the tips ! One more question. I have a reg/rec combo with nylon screw on the stator. Does this effect the pamco at all ?

 

[XSLeo]

No, the charging system only keeps the battery charged. The only effect the charging system has on the ignition is if the charging system ain't charging. The ignition works best with a well charged battery.
Well the whole electrical system works better if the battery is getting proper charge. Horn honks, turn signals flash. Stuff like that.
Once you get it running, check the battery voltage at idle it should read around 12.5 or so, then rev the engine slowly watching the volt meter, it should rise up to 14.5 volts by about 2000 rpms and never go higher than 14.5 volts at any rpm.
The 14.5 volts is a nominal reading. 14.3 to 14.7 is ok. much lower or higher then you need to do some checking.
Leo

 

[Michael xs650]

Thanks Leo, Ill check that tomorrow. Much appreciated, you guys are the best.