Super Jet Backfire out exhaust, Deaf & Hairless

billman100

billman100

Location
Seattle WA
Hey guys so I got my ski put all together after my build. I go to start it for the first time and get cranking but it wont fire. When i go to let off the starter it sounds like its turning over then nothing. Does this 2 more times then bang!!!!! Loudest backfire Ive ever heard. It came out the exhaust and blew my coupler apart from my b pipe head to chamber and a huge fire ball came out and got the hair on my arms. Why did this happen and how can I fix it??? Its a jetworks 850 motor so 62t cases, I am running a 61x stator and flywheel set to the stock mark on the 62t cases. Also cdi is an msd enhancer, supposedly pulled from a running ski, along with the stator, came wired together. Never seen such a huge backfire out the exhaust. Don't know where to go from here.

EDIT: also just check with plugs out on top of head, they only spark when I let off the igniton, same time the backfiring was occured, what could cause this?
 
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mike b

mike b

Michael "Mayhem" Bevacqua aka MikeyChan
Location
California
Well if you are running a 61x stator make sure that everything else is a 61x. Besides that maybe someone else has something, ive never had much issues with backfires
 
CRJ

CRJ

Hibernating
Location
Toronto
Thats would be a dumping of fuel into the exhaust then the spark finally making its way out of the cylinder. As to why, could be a few things but the stator is where id start, then the CDI. make sure it didnt split your waterbox. over priming the motor can do this too, if its flooded and by chance the cylinder ignites the fuel in the pipe.
 
billman100

billman100

Location
Seattle WA
I checked the wiring of the whites, they were hooked up correctly, I also disconnected the black plug from the start switch and got the same result of only sparking at let off of ignition. How do I ohm out the stator as the second post suggested? I have the ebox open on top of my cylinder, does it require pulling the flywheel off to get to the stator?
 
CRJ

CRJ

Hibernating
Location
Toronto
you can ohm the stator from the e-box wires that go to the stator. you need a volt meter, just google how to check ohms once you have one. Its very easy, its checking how much resistance a circuit has. (kind of like how hard it is to push the signal through the wire) higher is often bad, none at all means the wire is broken somewhere and there is no loop or circuit.

heres the specs for a 61x.for these you would put the meter in the ohm mode, and then put your black lead from the meter to one wire, and the red lead to the other wire listed below. if the reading is outside the numbers included you could have a bad stator.

charge coil resistance: brown/white-black 328.5-401.5 ohms

pulser coil resistance: white/red-black 12.6-15.4 ohms

lighting coil resistance: green-green 0.81-0.99 ohms

Primary coil resistance: orange-black 0.078-0.106 ohms

Secondary coil resistance: high tension cords: (plug wires) 3.5-4.7 ohms
 
billman100

billman100

Location
Seattle WA
Well I headed back out to the garage and the only one I got any reading on was the charge coil and it was about 350. The pulsar and the lighting coil didnt register anything and I wasnt sure where the primary and secondary where because my stator only had 5 wires coming from it. The ground, the two greens, which I couldnt get any reading from, and then the brown and white wires.
 
CRJ

CRJ

Hibernating
Location
Toronto
sorry you can disregard the last two, not sure why their listed in the link i followed. The first 3 will be there. if the gree-green is a 0 id pull the flywheel and look at the stator, it could be damaged. you can also try to ohm it closer to the stator, as the break could be in the wire going to the stator itself.
 
billman100

billman100

Location
Seattle WA
Got a brand new stator from JSS, installed, got everything back together. Went to start it and it cranked a few times and started right up, it was revving a little high for my liking, probably only let it run for about 3 or 4 seconds. Killed it. Went to start it again and BANG another backfire out the exhaust. I checked the plugs for spark before I tried starting in the first time and it seemed to be sparking normal, different than before with the old poop stator. I'm scared to try and start it again for fear of another huge backfire and blowing something up. I didn't prime it at all just either when I started it up. Seems like I could possibly have too much fuel in there or its leaking fuel in the carb?
 
O

octane972

Location
Burnet, Tx
If it was running fast when you shut it off, the momentum of the engine would keep it spinning long enough to pump quite a bit of unburned air/fuel mixture into the exhaust. When you started it again this mixture ignited causing a backfire. I would turn the idle down and try it again. If it continues to be a problem you probably still have a ignition or sparkplug problem.
 
JT_Freeride

JT_Freeride

John Tetenes @Jtetenes
Location
Long Island
That MSD is shot. I had the exact same problem I bought a "good used MSD" put it in but I didn't take off my battery and most likely fired the MSD on my own. But exact same problems you are having, I thought it was the white wires as well we ended up putting the MSD in a running ski with MSD and swapped them and same problem. Bought a new MSD and she runs fine. Swap your cdi with a known good one.
 
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