701 backfiring

[lil_stewie7]

Just picked up a square nose with a 701 in it. Have no history on the ski except it needs work. Starts fine and seems to run good until reved up then it backfires. Any help on fixing this would be awesome. Trying to get it on the water for this weekend.

Thank you

 

[Vumad]

Does it have a msd enhancer.

 

[lil_stewie7]

Does it have a msd enhancer.

Far as I can tell it's all stock

 

[Vumad]

My only experience with backfiring is the msd on my Superjet was causing backfiring before it failed.

 

[lil_stewie7]

If it is loading up with to much full at the top end, would that cause a backfiring?

 

[lil_stewie7]

My only experience with backfiring is the msd on my Superjet was causing backfiring before it failed.

How bad was it backfiring?

 

[jetskithegnar]

My stock Blaster backfires all the time when i start it.

 

[lil_stewie7]

My stock Blaster backfires all the time when i start it.

Just once? Or does it keep doing it until it warms up a little?

 

[Big Kahuna]

Water in gas can cause it. Also your flywheel key could be sheared.

 

[jetskithegnar]

Just once? Or does it keep doing it until it warms up a little?

Usually only once.

 

[jetskithegnar]

Water in gas can cause it. Also your flywheel key could be sheared.

I always thought backfiring was from excess fuel getting into the exhaust?

 

[Big Kahuna]

That two. But if your key was sheared and your flywheel has rotated then your timing is off. Now during the rotation of the crank you can get a point where there is fuel charge and open exhaust and then you get the signal for the spark to happen..............Bang......... you just had what sounded like a backfire but was really a premature combustion.

 

[lil_stewie7]

That two. But if your key was sheared and your flywheel has rotated then your timing is off. Now during the rotation of the crank you can get a point where there is fuel charge and open exhaust and then you get the signal for the spark to happen..............Bang......... you just had what sounded like a backfire but was really a premature combustion.

Ok so what is the easiest way to check if the key is broke off

 

[SmittySX]

Start simple.
-Put a new set of plugs in.
-Drain the gas tank and put fresh gas in.

 

[lil_stewie7]

Start simple.
-Put a new set of plugs in.
-Drain the gas tank and put fresh gas in.

Yep the plugs only have a few starts on them and just mixed the Gass a few days ago

 

[Big Kahuna]

Ok so what is the easiest way to check if the key is broke off

Pull the flywheel.

 

[lil_stewie7]

Pull the flywheel.

Yuck

 

[FlightPlanDan]

My only experience with backfiring is the msd on my Superjet was causing backfiring before it failed.

My stock CDI did this as well. Ski would run great until I shut it off. Then it would not start for an half hour or so...backfiring the entire time. Replaced it with an MSD and been good since.
But all that backfiring blew a bunch of air leaks that I didn't want to deal with. Jetmaniac/Blue got me back on the water.

 

[lil_stewie7]

If it is the CDI can I use a 650 one?

 

[Roseand]

If it's a 61x stator yes, otherwise you'll need to make a jumper wire. Just has a lower Rev limit.