popping back through carb on #3 cylinder

[sarchin]

Yesterday I was syncing the carbs and every so often there's a little pop of air coming back through the sync port...maybe every 10 seconds or so, otherwise there's a vacuum there. The little pop is strong enough though, that it will blow the sync hose off the port after around 5 or 6 pops.

I also noticed when I was changing plugs that there looked like there was air blowing past the spark plug but it was barely finger tight so I figured it might be that.

Compression on the cylinder was 165, and held that for around 5 minutes before I removed the tester to check the other cylinders, and the other cylinders were in the 160 to 170 range.

I'm not sure if I'm losing antifreeze yet, as I haven't noticed the overflow tank losing antifreeze.

If the rain quits I can get a short video of it by hooking up the synchronizer and you can see when it happens as it pushes the rod down.

What are your guys thoughts? Thanks in advance for any help.

 

[tugla]

does it sync before the pop....and how is the plug on that cylinder....any wetter then the others. just thinking maybe float not seating fully and leaking fuel a bit....

 

[sdt354]

Scratching my head, but I'm thinking, lean carb condition?

 

[Rusty McNeil]

If pop through carb occurs at idle or from off idle when just a little throttle is applied it is "usually" a lean pop that can be corrected by a little more out on the idle mixture adjustment.
That's assuming there are any other contributing issues like vacuum leaks etc....

 

[sdt354]

Where are the mixture screws at? I'd remove all 4 and make sure all the parts are where they're supposed to be. Clean.
Outside of that, how does it run?

 

[Mr. Max]

Might be a cracked rubber boot, better change them all at once if they look cracked.