1999 suzuki quadrunner 500 4x4 its starts and idles fine but key (lights off) it backfires key(lights on) doesnt backfire but it doesnt always go like that either. what would it be??

Question edited for FULL 'make model (what it is)', from 'banshee'.
Question moved from Motorcycles to correct Category.

Check spark plugs.
Clean Carb.
Check timing.

More here, it is a known issue.

https://www.google.com/search?q=Yamaha+banshee+atv+backfires

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Question edited for full year make model.
Question moved from Cars and Trucks category.

You are not alone with this issue. Check out the videos and written articles.

https://www.google.com/search?q=2007+kawasaki+brute+force+650+misfire

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Hi there,

Have you check the valves and the valve gaps?? Sometimes but not always having the wrong valve gaps can cause backfires. Have you also tried tweaking the carburetor to try and improve the idle??

I take help from online websites that have this service like helping in repair some like reliable-store have instant help.. others are a bit slow which I don't prefer... rest is up to u.. U can also get free manual works fine .

Here ya go Tony...

free manual for 1999 suzuki quadrunner 4X4 Google Search

backfiring is usually a sign of an air leak in the intake manifold

Hi Raymond,
This sounds an awful lot like a safety switch issue. A lot of ATV's now have safety switches which need to be deactivated otherwise the safety switch sends a signal to the ECU telling it to impede or delay the timing. So on your model I believe you have to pull the clutch in before you attempt to start it. AND you have an emergency brake safety switch. The emergency break safety switch can be activated if the emergency brake lever has been removed or if the pivot point is heavily worn, or if the rigging is wrong. All of these things will cause the lever to contact the switch improperly. And so your ATV thinks the emergency break is on. Basically your ATV thinks you're crazy for trying to accelerate while the break is on so it impedes or delays the timing so you wont hurt the ATV or yourself. And that's why your getting a nice idle but backfiring and sputtering when you try to accelerate.
Hope this helps. Good Luck

your carb may need cleaned or a dirty air filter

you can either use RTV silicon or JB weld for a permanent fix

carbon on the plugs indicates flooding
the backfire indicates fuel being ignited in the exhaust
have the carby /fuel system professionally overhauled