Hi There, i just finished putting new pistons and rings in my '78 Polaris S/S340 and now the beast won't start. I have checked that there is spark and the fuel pump is pumping gas perfectly and the compression is pretty good. I have also changed the ignition switch and still nothing. I pull and pull and it seems to wanna go but no fire. the odd time it will back fire and some smoke comes out. I have dumped a bit of gas down the cylinders and she still doesnt go. The choke cable is working fine and also the throttle cable. The carbs are clean and thats all i know. I have spent so much time and love on this thing and now im pretty much ready to give up. I need help with this thing. Any suggestions? I dont wanna have to take it to the dealer. this was supposed to be a cheap fun sled. Please give me some suggestions/help!!!!!!!Thanks.

Does it have good compression, is the timing right? The reason I say timing, is because the back fire.

Yeah it has good compression. I spoke to a buddy about it and he said to check the timing as well. The thing is......i dont know how to. Could you explain how to check and set the timing on this sled? Thanks a lot...your help is greatly appreciated.

I had a 76 Colt 340SS with a scored cylinder that acted like that. I'm sure a compression test would've helped, because by pulling on the starter roper, I couldn't feel the difference. For some weird reason, one of the rings decided to break off, and the broken piece embedded itself into the piston skirt, causing the scoring.

That sux. I got the 78 finally going. Went home after work and gave it a few pulls and it was alive. broke it in nicely then ran it hard all weekend. Ran great even with my Made In Taiwan pistons and rings in it. Gonna be alive for a good few more years. Gotta love the vintages sleds.

My next guess would be, you might have it flooded when you poured some gas down in the cylinders. Glad you have that thing running. WL