Motorcycle 4 stroke, ran great yesterday, it has brand new oil and coolent, and today it wont start and all it

does is backfire, really loud. what is wrong or what causes backfiring.Motorcycle 4 stroke, ran great yesterday, it has brand new oil and coolent, and today it wont start and all it
You didn't mention what kind of bike you have, but the same principles for troubleshooting apply.





Backfiring on a 4-stroke is usually caused by a carb problem or vacuum leak.





First ';read'; the plug(s). If they're black, it's been running too rich. Were you running it with the choke on yesterday? Has the bike been in storage for a while? Old gas after winter? If they're wet with gas, it's flooded.





Clean the plug with a wire brush and put it back in, leave the choke closed (off) and hold open the throttle all the way. Crank the bike this way until it starts. This should work for a flooded bike.





Also check for loose or cracked vacuum lines, missing rubber caps on your intake manifold or other possible source.





Check the carb to make sure the float isn't sticking. Drain and pull the bowl, check the float, needle and seat. Look for dirt, debris, pieces of rubber or varnish. If you've had the bike stored for the winter, this is a possibility. Check for proper gas flow also.





If none of this works, check the plug wires and coil connections. If your bike has a battery, check it to make sure it has enough voltage to operate ignition ECU. Most bikes need at least 8 volts to the ECU in order to function. If it's only firing once in a while, it may need to be trickle charged.





Good luck!Motorcycle 4 stroke, ran great yesterday, it has brand new oil and coolent, and today it wont start and all it
check the plugs. i betcha they're as black as the ace of spades. if they are, the carb is set too rich
Remove spark plug: look at plug if its wet your flooding it out But check spark by placing it back in cap lay it on cylinder w/ plug touching metal and kickstart it while looking to see spark...yea fun...If big wht spark good.


If spark is good but plug was wet %26amp; smelled of gas then take saprk plug completely out and kick over engine about 5 tmes to air out cylinder of fuel. Then replace spark plug and try again but sounds like it could be carb prob.
A fouled spark plug will cause backfiring.
If its a dirt bike and you said it's a 4 stroke. You may have lost compression. A 4 stroke dirt bike has to have the top end built every 15 to 20 hrs of riding time and only 10 hrs if you run hard i.e dessert. I would start with the plug. But I'm sure that's not it. Good luck.
are we talking ';a no crank'; situation or wont run but still turns over?
try tipping bike on its side first. let any excess fuel pour out.





kick bike with fuel off 5 times and hold hot start open (im guessing it's a dirt bike).





kick the bike 5 more times with hot start closed...





then turn fuel on, kick bike normally... it really depends on the year, make and model of the bike.. this would help the diagnosis .