POPPING when I let off the throttle

[wpginterceptor]

Just got this BIG RED running and took it for a spin..

Seems like when I rev it up and let off the gas, she pops/backfires out of exhaust..

Any ideas to check?

[ylwgtr]

valve clearances or a lean mixture

[Xpress]

Probably jetted incorrectly.

[kb0nly]

Mine randomly does that to, 84 200ES, i have rebuilt the top end on mine, new carb, and gone through everything including a new exhaust over the last year or so, still randomly does it. Plug looks perfect color, not running too rich or lean, who knows. I don't worry about it none.

You should check the clearance of the valves and see what your plug looks like if its doing it constantly though. Mine does it depending on the weather and engine temp, etc. Usually if its a cold damp day it will pop once or twice until she it warmed up good then it goes away.

[Jason125m]

If you have even the tiniest leak in the exhaust it will pop. If it is lean it will pop. Only two ways it will pop.

[MOTOMAX27]

lean.. try to close the air screw a bit.

[fabiodriven]

Exhaust leaks are the usual culprit as Jason said.

[Yamaha_Rules69]

What year bigred? If its a 200cc motor, it would be a fuel screw, located under carb near the head, and out would be richer, and in leaner. Is the exhaust sealed tight, especially where it connects to the head?

[userj8670]

What year bigred? If its a 200cc motor, it would be a fuel screw, located under carb near the head, and out would be richer, and in leaner. Is the exhaust sealed tight, especially where it connects to the head?

I have this problem on my sx with a supertrapp. How would i seal the exhaust in tight to the head - now dont get the wrong idea but i mean its screwed in tight to the studs but are there additional things like a donut or something? As someone else mentioned my plug is perfect tan color **** however everytime i let off the throttle she pops as she unwinds to the lower rpms

[Jason125m]

I have this problem on my sx with a supertrapp. How would i seal the exhaust in tight to the head - now dont get the wrong idea but i mean its screwed in tight to the studs but are there additional things like a donut or something? As someone else mentioned my plug is perfect tan color **** however everytime i let off the throttle she pops as she unwinds to the lower rpms

There is a copper crush gasket at the head, buy a new one. Also, for the joint between the two pipes, they sell an aluminum exhaust gasket tape that works great.

[wpginterceptor]

YES mine is a 1984 Big Red 200ES

[kb0nly]

I put a new exhaust donut on mine when i did the rebuild, its a DG exhaust, though the stock exhaust used to do it randomly too. I retorqued the exhaust studs after a couple days riding to insure a good seal at the head. The only place my exhaust could be leaking is where the head pipe meets the muffler, and i think i will do a little further sealing there to rule that out. Makes perfect sense, on a cold day the exhaust is probably leaking there a bit until she warms up and expands and seals that joint, once its warmed up it never does a single pop.

[tanks350x]

adjust your mixture screw, thats all it is!!

[kb0nly]

If your talking to me, its surely not the mixture screw, its running perfect mixture wise examining the plug.

[oscarmayer]

in my expirences, if it's not a leak at the head and exaust flange, then that is not the poping issue. it woudl them be too much fuel dumbing when he lets off the throttle. a slight adjsutment of the mixture screw, possibly needing to adjust the needle, or evne wrong sized jet. you said you got a new carb. they don;t make these stock carbs anymore, so maybe the aftermarket is a different size and that size is not properly jetted for the engine? it can run proeprly under loads, but when letting off, the popping is usually fuel dumping and the hot exhaust pipe/gas igniting it in the pipe. no different than a car. Also timing can cause this by ignighting the spark too late.
Check all those things.my on son's racing ATV, it pops when he lets off after hitting the throttle hard, but that's because we have to run such a large jet due tot he fuel type and 15.5:1 compression on his 125cc ATV.

[userj8670]

Where can i purchase these copper crush gaskets for the exhaust. I never heard of them or noticed them for that matter.

[RodKnockRacing]

Where can i purchase these copper crush gaskets for the exhaust. I never heard of them or noticed them for that matter.
any atv shop or online

[El Camexican]

Aside from the likely exhaust leak mentioned by so many, the number one cause of popping on a single cylinder engine or “popcorn” on a multi cylinder engine is lean jetting, but not the main jet. It’s the pilot jet and air or fuel screw. Odds are on a stock setup the pilot is not so far off that it would cause this UNLESS it is plugged a little which is where I’m putting my bet in this case. If it is the screw then you have to determine if it is an air screw or a fuel screw. Air screws are located on the carburetor before the main jet (USUALY FOUND ON 2 STROKES) and fuel screws are located past the main jet nearer to the engine (USUALY FOUND ON FOUR STROKES). If it is an air screw you turn it in to richen the engine. If it is a fuel screw you turn it out. If at any time you find that the engine runs best with either screw opened more than 2.5 turns, or less than ½ a turn it is a sign that the pilot jet should be changed to the next size which corresponds with the problem. After checking the exhaust for leaks I’d open the carb, remove and clean the pilot jet, check that all the jets are stock and that the needle clip is set in the middle, or stock position and set the screw at 1.5 turns and try it.