carb #3 vac. port?

[mtalneck78]

I just read in an old thread where a guy was having problems with the #3 cyl. not firing. I am also having this trouble. My bike (79 GS750L) did not have a tank on it when I bought it, so I had no idea about the petcock vac. hose. I have rebuilt the carbs & am using an old lawnmower gas tank to get it running. Where is the fitting that needs to be blocked off on #3 carb? They all look the same to me. The manual didnt mention anything about this.

thanks, Dan C.

[ptm]

[SqDancerLynn1]

If you don't plug it The leak will not allow # 3 to draw fuel, or if the petcock diaphram is leaking it will foul the plug. THE same goes for the later BS carbs except it is the #2 carb

[mtalneck78]

Thanks so much for the info.

I have another stupid question. I thought those fittings where just vent lines. Where do the hoses on #2 & #4 carbs go to?

Great to find a place that will help out the new guys.

Dan C.

[ptm]

#2 and #4 have hoses attached that just vent to the air. On most early models they run up over the airbox and down the back side through a small bracket toward the right side. #1 doesn't have a vacuum nipple and #3 has a hose that runs to the petcock and provides vacuum to let the fuel flow only when the engine is running (that works if the petcock is set to RUN or REServoir). On PRIme fuel flows whether or not the engine is running. PRI should be used only briefly to fill the carb bowls after the bike has been sitting for a while.

[mtalneck78]

thanks Paul