'92 Seadoo 580SP backfires thru carb under load

[Riverrider]

We have a '92 Seadoo XP 580 the starts instantly when cold or hot and idles like new. But when throttle is about 1/4 on up to WOT it backfires thru the carb. Carb was gone thru already. It used to bog down but changed plugs and this thing will go full throttle but have an intermittent backfire that happens often. Compression is 127 in front and rear is 129. We bought it used and looks to have the grey fuel lines replaced with black hose. This does the same thing in and out of the water also.

 

[kustomkarl]

It might be either the timing of the stator plate in the Magneto, or if the rotary valve was removed it might be just a little out of time also. It sounds like a timing issue, for sure.

Karl

 

[Riverrider]

Don't I need special tools to adjust the timing? I see the manual says I need a 360 degree wheel and a bolt on timing tab tool.

 

[kustomkarl]

The Mag timing you just align up the marks for a static time. You need a dial indicator to degree in the Rotary Valve.

Karl