Super Jet Superjet Backfire - Not a normal backfire!

[ace6839]

Alright, so I took my 01 SJ out of storage to get running, which ran last year. This year I am turning it over and over, primed it a bit, normal stuff, then all of the sudden POP!! It sounded like a gun going off and it came out of the exhaust, what would cause this? It was not running and doesnt seem to want to start. I gave it some time (mainly cause I was freaked out) and gave it a go again. Same thing happened after trying to start it again. Seemed like this one came more from the engine compartment this time tho.
So, what is causing this? My set up is a stock 701 motor, 46mm carbs, B pipe, ADA head, nothing to extreme. Ideas?
Thanks in advance!

 

[SmittySX]

Same thing happened to me.. Im scared to mess with it because it was louder than a shotgun! From my research its most likely and electrical problem.. bad CDI, stator, or the woodruff key from your flywheel..

 

[ProSouth]

i'd check the water box to see if it didnt blow it apart. check electrical like smitty said. if that woodruff key slipped and its sparking at the wrong time it will cause backfiring.

 

[rubbertoe]

Leaky needle and seat . Can cause this , and would be my guess .if it ran good last time you used it ,then it sat .Good luck with your fix , hopefully something simple

 

[stefan]

Like mr rubbertoe said leaking needel and seat will put fuelt in the crank cases and when you put a spark too it gets LOUD dont think you got a elektrical problem you clearly have a spark.

 

[SmittySX]

Sorry to thread jack..
But i bet thats my problem... Leaky needle and seat. I rebuilt the carbs ( they were nasty), fired it up and it revved and idled in the garage, as soon as i went to the lake i fired it up on the trailer and it backfired and wouldnt start since.

 

[rubbertoe]

A large backfire could Cause the crank to suddenly change directions causing a shear at the woodruff key on the flywheel putting timing in a position where it won't want to start , not for sure but maybe something to look at ?

 

[orangefinger]

whatever you do air the out of the waterbox and exhaust before you start it back up....if the n/s is leaking the BOOM could be much bigger

 

[Vumad]

Like mr rubbertoe said leaking needel and seat will put fuelt in the crank cases and when you put a spark too it gets LOUD dont think you got a elektrical problem you clearly have a spark.

Backfires are often caused by timing issues, which are caused by electrical problems. A lot of things can cause them so I'm not saying it is electrical, just making it clear that the presence of spark does not rule out electrical causes.