Popping or bacfiring

[Guest]

Hi all,

i have a 79 gs425 with valve shims replaced and now in spec, carbs dipped and synced. I had loud backfiring last week and tried to dial everything in with the highest idle method and everything sounds pretty good. But. I took it out for a run this evening and didn't hear backfiring as much as popping and curious to know what you all think?

How do I distinguish between backfiring and popping and if it's popping what should I do next?

Thanks.

[tkent02]

Have you checked for exhaust leaks where the pipes come out of the head?

[Gs425FridayHarbor]

I just replaced the gaskets and don't know what else to do to find exhaust leaks? Thoughts?

and thank you tkent, as always.

[tkent02]

Can also be from a little extra richness, is it popping when the throttle is closed or when?

[Gs425FridayHarbor]

It's popping a little at idle and more noticeably on deceleration but not significantly, just small pops - if that makes any sense?

[Gs425FridayHarbor]

Also, it sounded like it was backfiring last weekend (not popping) but I had mixture screws at almost 3 turns and idle screw barley engaged. Now I have idle screw almost all the way out and idle screws at about 1.5 turns out and it idles pretty well with small pops which are more noticeable on deceleration.

[60ratrod]

check for vacuum leaks. popping at idle is a good indicator of being lean, and from those idle mix screw settings, it's probably a vacuum leak. I didn't see if you inspected the boots, or replaced the o-rings that go between the boot and the head. those are a notorious spot for vacuum leaks. your airbox boots could be leaking too. to check for leaks, use either sprayed carb cleaner or starting fluid and spray it around where the carbs slide in the boots on the head, between the head and the boots, and the boots around the airbox. if the idle changes when you spray around any of these locations(usually increases idle speed), you've found your leak(s). the backfire could be a bad coil/plug connection.