Popping on decel cause???

[TheChasers]

2008 Yz450f. Can someone check out video linked and let me know whats the possibilities for the popping on decel?

I have 48 pilot jet and 160 main. At 2700-3000 elevation...

Rebuilt top and bottom end, about 2 hours on it. Rebuilt carb, jets are brand new.

I have tried turning down idle and turning out pilot screw to richen some(maybe Im not tunring idle low enough to get perfect setting) but eventually pilot screw gets turned out to the point that just revving bike can move screw position(I have a WorksConnection after market pilot screw).

Im seeing a few possibilities online, like maybe air leak somewhere on exhuast, ect.
I also see online that supposedly some backfire is normal, but I dont know to what extent.

Just trying to see if an experienced rider can lead me to the best probable cause...

Popping Cause?

youtu.be

 

[SRAD97750]

Air leak at the header is 99% the cause of my 4Ts backfiring on decel.
While some 'snarl' is normal in a rich deceleration with the engine engaged, if it's popping the moment you let off or loudly or in neutral, it's most likely cold air coming in contact with hot/unburnt combustible gases in the exhaust.
It can be at the header, or sometimes as far back as the pipe to header fit. -BIG DAN

 

[TheChasers]

Air leak at the header is 99% the cause of my 4Ts backfiring on decel.
While some 'snarl' is normal in a rich decel with the engine engaged, if it's popping the moment you let off or loudly or in neutral, it's most likely cold air coming in contact with hot/unburnt combustible gases in the exhaust.
It can be at the header, or sometimes as far back as the pipe to header fit. -BIG DAN

Ok. Was watching a few videos and considering upping pilot screw to a 50 but I will go check and remove exhaust from header and put it backon trying to seat it better.
Is there any quick ways to immediately determine if I have an air leak where exhaust connects to header?

 

[SRAD97750]

There is a muffler gasket and a header seal, I would check their condition. If they are new looking, it probably fueling.
Usually these seals look pretty beat up and a quick replacement is great insurance about it being a future issue.
-BIG DAN

 

[SRAD97750]

Your manual states a #45 idle jet and 1.5 turns out from gently seated on the idle mixture screw as a start point at sea level.
Can't imagine you're far off at 3K feet. -BIG DAN

 

[TheChasers]

Your manual states a #45 idle jet and 1.5 turns out from gently seated on the idle mixture screw as a start point at sea level.
Can't imagine you're far off at 3K feet. -BIG DAN

Ok, so maybe it is an air leak because I richen pilot jet to 48 and still not much change in poppin.
One last question before I check exhaust. What caused me confusion and had me doubting air leak is because I sent video to friend and he said it couldnt be an air leak because if it was, that ny throttle would hang. Im trying to learn signs and symptoms as I go, so is that incorrect? Is it possible to have a small air leak without seeing symptom of throttle hanging?

 

[TheChasers]

Your manual states a #45 idle jet and 1.5 turns out from gently seated on the idle mixture screw as a start point at sea level.
Can't imagine you're far off at 3K feet. -BIG DAN

I had this too far down, where the curved tip circled isnt seated at top like it should. Seems like that could possibly let out some air. Enough to result in poppin?

 

[TheChasers]

Was hoping that was the issue... I even turned screw ALL the way out, still poppin on decel.
Only thing I didnt check the needle jet and clip. Since previous owner changed to a richer pilot jet, maybe he leaned out the needle jet. Idk but might as well check it. Ima look up some videos, see if its possible to change needle and clip withiut removing whole carb

 

[SRAD97750]

Ok. Was watching a few videos and considering upping pilot screw to a 50 but I will go check and remove exhaust from header and put it back on trying to seat it better.
Is there any quick ways to immediately determine if I have an air leak where exhaust connects to header?

Adjusting the idle fuel mixture screw out will provide the same results as a larger jet to a certain point. If more fuel at the mixture screw helps the situation, then a larger jet may be needed. I don't see a lack of fuel being your issue at all.

Ok, so maybe it is an air leak because I richen pilot jet to 48 and still not much change in poppin.
One last question before I check exhaust. What caused me confusion and had me doubting air leak is because I sent video to friend and he said it couldnt be an air leak because if it was, that ny throttle would hang. Im trying to learn signs and symptoms as I go, so is that incorrect? Is it possible to have a small air leak without seeing symptom of throttle hanging?

Idle mixture can cause a hanging idle if it gets too lean.
The exhaust system is after the cylinder, which has no effect on idle mixture.

I had this too far down, where the curved tip circled isnt seated at top like it should. Seems like that could possibly let out some air. Enough to result in poppin?

No, probably not the culprit. That gasket looks pretty good too.

Was hoping that was the issue... I even turned screw ALL the way out, still poppin on decel.
Only thing I didnt check the needle jet and clip. Since previous owner changed to a richer pilot jet, maybe he leaned out the needle jet. Idk but might as well check it. Ima look up some videos, see if its possible to change needle and clip withiut removing whole carb

Food for Thought
What is the 'Popping?'
A rich condition causing unburnt fuel to mix with cold (oxygen rich) air leaking IN at the header, which allows combustion to continue in the exhaust pipe.
This requires extra fuel, more than the engine needed to run. A rich condition.
If you were running lean on idle mixture, there would be no extra fuel in the exhaust to 'pop.' Infact it would backfire out the carburetor and intake side in a lean condition. The fuel comes from that direction.

Remove the header and inspect the header seal up in the head. It may be folded over or pinched.
-BIG DAN

 

[Rolls]

If the bike still has the smog stuff connected it would also pop on decel.

 

[TheChasers]

If the bike still has the smog stuff connected it would also pop on decel.

Can you explain what that is?

Also to anyone suggestion. Valves clearance is perfect, all at top end if spec. Timing was perfect still.
What I noticed when getting ready to put valve/cam cover back on is that Im able to pull back gasket on exhuast side with my finger.Not able to pull back intake side. Is it a chance air can seap thru enough to cause popping?

 

[SRAD97750]

Can you explain what that is?

Also to anyone suggestion. Valves clearance is perfect, all at top end if spec. Timing was perfect still.
What I noticed when getting ready to put valve/cam cover back on is that Im able to pull back gasket on exhuast side with my finger.Not able to pull back intake side. Is it a chance air can seap thru enough to cause popping?

Interesting, You checked the valves after running it for a bit? Valves could also 100% be an issue. I didn't realize this is a fresh build. I wrongly assumed a new issue. If they are correct, they are correct, though.

That oil seal is to the crankcase and not involved in the engine fueling.
-BIG DAN

 

[TheChasers]

Interesting, You checked the valves after running it for a bit? Valves could also 100% be an issue. I didn't realize this is a fresh build. I wrongly assumed a new issue.

That oil seal is to the crankcase and not involved in the engine fueling.
-BIG DAN

Appreciate you addressing all my questions. Yes I just checked vavles. Timing and vavles perfect.
Honestly, I thought "popping" and backfire was one in the same. And whenever I look stuff up online everyone is saying Im running lean. Thats why I left the 48 pilot jet in even though stock is 45, as well as moving needle clip down 2 notches to rich it some more to combat the poppin/backfire.
I was just calling around everywhere trying to get a replacement valve/cam cover gasket, lol. Was thinking maybe air could get in and cause my issues but since you said that has no affect what so ever, Ima go back out and pull exhaust at header off right and see whats up

 

[SRAD97750]

The popping you hear is referred to as 'Afterfire' as it happens in the exhaust after the common power stroke.
A backfire refers to the uncontrolled explosion coming BACK out the intake. These can be very damaging to components and people.
Big 4bbl V8s love to backfire right in your face.

Afterfire is common in over rich conditions or re-ignition situations where there is too much fuel in the exhaust. It can also happen if the valves are hanging, or too tight. The combustion chamber literally is open to the exhaust through the hanging valve that was supposed to be shut.
Back fires are common in lean situations as the over-stoichometric fuel condition can burst quickly back through the open intake valve that is feeding the hot cylinder.
-BIG DAN

 

[TheChasers]

The popping you hear is referred to as 'Afterfire' as it happens in the exhaust after the common power stroke.
A backfire refers to the uncontrolled explosion coming BACK out the intake. These can be very damaging to components and people.
Big 4bbl V8s love to backfire right in your face. -BIG DAN

Afterfire is common in over rich conditions or re-ignition situations where there is too much fuel in the exhaust. It can also happen if the valves are hanging, or too tight. The combustion chamber literally is open to the exhaust through the hanging valve that was supposed to be shut.
Back fires are common in lean situations as the fuel can burst quickly back through the open intake valve that feeding the hot cylinder.
-BIG DAN

Gotta ask because I dont know, so just want to eliminate all possibilities.
These 2 dents in exhaust can or cannot contribute to the popping?