Engine pops and crackles

[nupmeyer15]

Just read through this....
On my predator 212, I adjusted the idle screw on the carb so that when the engine decelerates, the engine pops and crackles. It sill revs up fine. Is this safe for the engine?

Also got a custom intake on it and a custom header

 

[OzFab]

Even if you have an identical condition described in an existing thread, please start your own thread as opposed to hijacking someone elses thread...

The usual cause of popping &/or crackling on deceleration is an exhaust leak; it's not ideal but, it shouldn't harm the engine...

 

[bob58o]

Does it snap, or only crackle and pop?

---------- Post added at 03:15 AM ---------- Previous post was at 02:56 AM ----------

These will give you a pretty good idea as to how to set the idle mix fuel screw.

Better than me trying to explain.

You basically are looking for a setting, between the lean and rich stumble, with the highest RPM, without a hesitation when you hit the throttle, and that quickly returns to idle RPM without hanging up at higher RPMs when you let off the throttle. Sometimes a perfectly tuned carb will backfire upon deceleration.

Predators have a FUEL screw.
https://www.youtube.com/watch?v=YxpQjDQzX7g
https://www.youtube.com/watch?v=zm5mB3R8Ucw

 

[bob58o]

You might need bigger carb jets to match your intake and exhaust.

 

[PredatorPowaaa!!]

how would the idle screw make the engine cradle and pop?

____________________________________________
"I'm pretty sure that 91 octane runs trough my veins"

 

[bob58o]

how would the idle screw make the engine cradle and pop?

____________________________________________
"I'm pretty sure that 91 octane runs trough my veins"

If idle speed screw then IDK, but if idle air/fuel mix screw it would becuase....
when you close the throttle (Decelerate) the engine runs off the carb's idle circuit.

Sometimes a lean intake charge won't burn correctly which allows the charge to get into the exhaust.



What causes Backfiring
http://www.rcramer.com/shop/backfire.html
"Deceleration Backfiring" is the most common backfiring that occurs when you change down and throttle off. This extract from the Virago Site explains it succinctly.
"In general, backfiring on deceleration (as opposed to acceleration) is generally caused by a lean condition in the pilot circuit. What happens is that the mixture leans out enough to where is fails to ignite consistently. This, in turn allows some un-burnt fuel to get into the exhaust pipes. Then when the engine does fire, these un-burnt gasses are ignited in the exhaust pipe, causing the backfire. Newer Virago carbs have an 'enricher circuit' which cuts in on deceleration to help this problem. Earlier carbs do not have this. I would say check the pilot circuits, and set them a bit richer. It is hard to do this right without some equipment to test where you are. Aftermarket pipes often increase backfiring, probably because they may the bike run leaner."

 

[PredatorPowaaa!!]

Just read through this....
On my predator 212, I adjusted the idle screw on the carb so that when the engine decelerates, the engine pops and crackles.

oh i know that the idle screw wouldn't cause backfires, i was just saying that so he would correct himself.

 

[BoostedBaja]

Pops and crackles out of the pipe? If it doesn't have baffles than that's normal. Unburned gas. Doubt adjusting the idler would have changed anything either.

 

[Flyinhillbilly]

Opening the idle screw will expose more of the transfer ports causing it to draw more fuel at a low throttle angle/ high vacum situation.

 

[bob58o]

Opening the idle screw will expose more of the transfer ports causing it to draw more fuel at a low throttle angle/ high vacum situation.

If your clutch allows, I supposed you could set idle high enough where this "problem" will go away, but I feel this is kind of a band-aid, or am I off?

 

[Flyinhillbilly]

It's kind of a double edged sword. If you uncover the transfer ports too much you can cause an off idle stumble (car experience here, not go kart, but should work the same) I'd try going up a touch on the pilot jet and see if that fixes it. In my opinion it has a good chance at it.

 

[bob58o]

One day I'll get ballsy enough to pop off a welch plug on one of these Predator carbs and play with the transfer/transition holes. Heard 0.002"bigger makes a difference. I was actually looking to cure a lean bog when accelerating when I stumbled on this info, but seems like the same issue?

 

[Flyinhillbilly]

What we do on cars is drill a small hole in the butterfly to allow extra air while keeping the transition slots adjusted right. Your big cam probably had your butterfly open enough that it was already running on the whole thing.