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paul d

500 quadmaster sputters an backfires after warmup

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hello everyone , i bought a suzuki 500 quadmaster 2 years ago , it wasent running , the guy said he an his dad broke the choke cable attempting to take carb apart so he just put it in the shed , i got it an rebuilt the carb put new choke cable , battery , spark plug , petcock , air filter , changed oil , after some adjustments got it running like a new one , at the end of spring this year i got on it to go for a ride , after about 2 minutes it stalled running real rough an backfirering , an woulnt move , but at idle it runs fine , so i put a new carb on it , same thing runs fine for about a minute then sputters an backfires , i took the new carb back off an cleaned an put the factory carb back on , i check the petcock , it was brand new an i cleaned the tank thougholy when i put it in , everything still looked fine , checked the air filter , it still looked fine, also checked the sparkplug , back in may i took everything apart ,"again" cleaned it put it back together , didnt put any gas back in it an gave up on it , just recently my grandson wanted to look at it so i put some gas in it , it fired right up but same thing after a minute sputters an backfire , i'm at my wits end , i posted my problem on here before an tried everything i got in the responses , any help would be so greatly appreciated, thank you for your time in reading this rediculously long post

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I would check the spark plug color after it starts acting up.  See if it’s dark and fouled.  

If so then your fuel mixture is off. Stick with the oem carb and set the mixture screw as per spec and maybe a slight adjustment. But first check what your spark plug looks like as soon as it starts acting up.  Black color  bad, nice light brown color  is good. 

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I'd try a new NGK plug.  They're $2.49 and may solve the issue.  Plugs often malfunction under pressure and you can't see it inside the chamber.

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thank you for the reply's , i've adjusied the air mixture screw , checked the float, an the spark plug , everything looks fine , i've spent a lot of time taking this thing apart an adjusting , i'm not a schooled mechanic but i have 50 years exp. of working on my own trucks boats an tractors an yes atv's , this one seems to be beyond my knowledge, it doesent make any sense. i've went over everything , looked for air leaks in the intake i put a new no-toil air filter in , changed the plug again just make sure, could it possibly be a problem with the oil pump? i dont know how to check it on this machine

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Check your exhaust is clear and has no obstructions.  

The only other thing I can guess it to start testing your secondary coil  with a tester.  The specifications for the acceptable range are in the manual.  Double check the ignition coil is good, check the rectifier etc.   It costs nothing to check all of them and can be easily done.   I don’t really think it’s an ignition problem and prob just a carburetor adjustment but at least it’s another avenue to go down.  

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Check the voltage across battery terminals while running at idle and revved up.  I have seen a lot of these issues for people being resolved if the voltage regulator/rectifier goes bad.  I am having a similar issue and have a regulator on the way as mine was not providing voltage at all while revving.  Hoping this is the fix so I can finally ride my bike.

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