[Benmiller1]

2019 Polaris sportsman 570
Recently I was out riding when I got water in the oil and blew up the motor on the fourwheeler. I pulled the motor out and did a rebuild on it, put a new crank shaft, new bearings and decided to go with a 104mm big bore kit. Since I did the big bore kit I put on a big gun efi tuner and a big gun exhaust. On initial start up it fired right up and ran and idled perfectly but after about 5-10 minutes of running it shut off. Went to start it back up and it won’t run at all any more it back fires flames but won’t run anymore. So I started the basic checks, I checked spark and it was good then decided to put a new spark plug in it and it still didn’t fix it or make it run. So then I went to the injector and took it off and spun the motor over, it’s shooting fuel out like it should. So it has spark and fuel going to the cylinder. So then I thought maybe the timing had jumped I checked the camshafts on top and they looked one tooth off so I turned them both one tooth but still same results the fourwheeler just back fires. I’ve done all I can think to do at the moment is there anything else I could check to see why it won’t run? Please help.

 

[FPD218]

to the forum

 

[latebird]

What about spark timing? Most common mistake is failure to tighten the flywheel sufficiently and the flywheel key shears and then the spark timing is off. Don't confuse spark timing with cam timing. If the flywheel slipped and you changed the cam timing based on the position of the flywheel without verifying the piston being at TDC and it turns out the flywheel key sheared, you will have to retime the cams in reference to piston position (must be at TDC). The other possibility is the 'tuner' you installed. Remove it and see if it will start.