ski is back firing at 1/8 throttle

Maxumflux

Maxumflux

Location
Knoxville, TN
my yamaha sj is back firing at about 1/8 throttle. i pulled the head and one dome is black with oil and the other is clean. could the spark plug be my gremlin? both cylinders are getting a spark. the back firing started after i found part of my flame arrestor lodged in my reed cage. i pulled it out and she is still kicking at 1/8 throttle. does any one know why it is back firing after i cleaned my reeds? im thinking the plug may be going bad. :smashfreakB:
 
Waternut

Waternut

Customizing addict
Location
Macon, GA
Well the cheapest and easiest solution would be to replace the plug and find out. If the clean cylinder looks like it's almost new, you probably blew the head gasket and water is seaping into the cylinder and steam cleaning it. The other possibility is one of the reeds is broken or damaged and letting too much air into the one cylinder and leaning it out real bad.
 
Maxumflux

Maxumflux

Location
Knoxville, TN
the one cylinder looks normal but the other is dark black. like it is extremely rich. the reeds were fine. there was a metel wire holding one of them open. i pulled it out and its all good. im thinking that oil accumulated and wouldn't let the gas explode like normal after i cleaned the reed. i guess ill wipe it clean and try to fire her up again
 
kawyjunki

kawyjunki

NODNARB
Location
Springfield,Branson,Mo
xkawi550x said:
alright i am getting new plugs. how do i torque the ada head? do i need new head seals?
Click to expand...

If you have new o-rings for the head I would put them in pretty simple and easy process and rule out any problems with them at that point. Torque the head in the same sequence as the stock head, working from the inside bolts out in a clockwise pattern. Torque the head bolts around the domes to 20-23ft lbs and the girdle bolts to 25-28ft lbs. Some may have a different opinion on these rates but this is what I do. And be sure to bring it up to full torque slowly, like 15lbs then 18lbs and so on. Then after final torque go over them again.

I added a small diagram of the head, hope this is understandable. The outer numbers are the girdle bolts. Inner circles are sparkplug holes.
 

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kawyjunki

kawyjunki

NODNARB
Location
Springfield,Branson,Mo
turbo626 said:
torque those girdle bolts to 35ft lbs per chuckie at team scream.
Click to expand...
On the earlier style girdle bolts, like I have on one of my motors, I heard they were a bit weaker so I try to stay safe on them, with a lower torque.Of course its also not running 200+psi compression either. LOL!! If this is just rumor, I would like to know for sure? From the pic in Xkawi's Avatar it looks to be the older style head. So I went with that.

xkawi550x said:
where do i buy new orings?
Click to expand...

http://www.adaracing.com/parts/personal-watercraft/o-rings

or go to this thread, and scrll down to the o-ring section:
http://www.x-h2o.com/threads/31581&highlight=Official+Mcmaster+Carr
 
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