Super Jet backfire

[joecef]

Hey guys I need help. So I just installed my new motor 760 with 449 carbs am cdi everything else electrical is stock. Made sure my timing was right. So I went to start her up a month ago poured some fuel down the carbs. She fired right up. Great. So yesterday I go out do the same thing maybe a little to much fuel and hit the start button and maybe 6 sec into turn over backfire. Not a small back fire buy a shot gun like back fire. So I let her sit. Went ran all the fuel lines today attempted to start it crank crank crank. And a ball of flame threw my hood off and now I'm lost. Any help from here. As far as smoke and such seemed to be coming from exhaust. I turned it over by hand and nothing out of carbs. Any help would be great at this point and time

 

[joecef]

44mm carbs

 

[Fx1 Love/SJ Love AZ]

i just put my fx together and she backfires nasty. How i see it it could be the gas doesnt like to sit for a long time thats one thing. other than that sparkplugs and other simple stuff. you obviously dont want it to explode or catch fire, but with mine i got it started and let it run and backfire all it wants as long as it idles good and stays running. i hooked mine up to the water and ran it for a couple minutes and let the motor just idle and blip the throttle and really feel for the backfire. mine will always backfire when i rev it all the way to the limiter and let off. i can recall a few times it would backfire right on the startup but its just a backfire. as for why or how it blew your hood off who knows? that would take alot of air coming out of somewhere in the engine compartment. make sure everything is very secure, all the hose clamps etc.

my friend told me when i asked him about mine backfireing is that it was most likley that my fuel has been sitting for a month or 2 or 3 haha and also changing my sparkplugs helped. it was about time for plugs anyways as i have ridden probably 20plus times and mostly all day rides in wich im WOT atleast 75% of the time so that was smart.

 

[joecef]

I'm going to try to start with brand new plugs. The gas I'm using is 91 and it's about 3 days old. I filled my tank up the other day with it. I've red a few other posts about bad backfire and not starting just backfire but never a conclusion in any of them.

 

[Kohldanielzimmer]

I would start looking into the flywheel/ stator. Perhaps the woodruff key sheared and it spun the flywheel

 

[Fx1 Love/SJ Love AZ]

yea plugs first, but thats odd. i run 91 only as well even though its a stock motor, but the question is can you get it to run and idle. if you can get it to run and idle but it backfires then it could be something like too rich or too lean, im not the guy with all that factual knowledge on that. but i can say my fx1 backfire like a son of a b yet it still idles perfectly and revs up and returns to idle just as it should. we stuck a cup to the end of the exhaust and made it backfire itno the cup and after like 5 trys of it blowing out of out hand we finally got it perfect and the cup exploded. definitely had alot of backpressure but nothing to the extent of feeling like it would blow an exhaust hose off or anything.

 

[joecef]

I'm going to look at fly wheel again tomorrow i looked the other day nd the marks still lined up. But after the explosion today who knows

 

[Fx1 Love/SJ Love AZ]

if its not the plugs it has to be the timing. thats what is telling it to fire apropriately and on time. if its not a small normal backfire then its probably something alot more serious. especially if it blew off your hood with fire haha thats crazy!

 

[joecef]

No she won't start just cranks for 10 sec and bam bikini back fire.

 

[joecef]

Hahaha bikini backfire. Biiiiig backfire

 

[Magyar68]

when Mine Backfired while riding at speed it was the OEM stator going out. Pulse coil was just past the service limit.
When Mine backfired and would not start at all is was because of a WSM replacement Stator, they are all bad from the factory.

 

[Magyar68]

I have also heard of this happening with AM ignitions when the Battery is about to Die, but can't find the Post.

 

[Quinc]

Does it only backfire when you let go of the start button?

 

[joecef]

I'm going with timing jumped. I forgot my puller at work today so not going any further.

No it backfires when. Trying to start with my finger on the start. The start stop switch is okay. I already cut that out by just jumping it without the start button.