717 backfire through the carbs

[vogs77]

I am going to be working on a friends ski, 97 GTI that is backfiring through the carbs. It had a new motor put in it last year and it started having trouble at the end of last season. It doesn't like to go above 3500 rpm either. I don't think the fuel system has been rebuilt yet, the owner did think they did it at the time the engine was put in. Is this usually a symptom of a carb issue? I was planning on doing the whole fuel system like I did on both of my skis but wasn't sure if there was something else I should check before tearing it apart.

 

[mikidymac]

Backfire could be the rotary valve either timed wrong or stripped.

 

[vogs77]

It ran good for most of the season and when he put the ski in this year it was ok until this weekend. Do you still think it could be a timing issue? Is it worth it to try a fuel system repair?? It idles good and runs ok up to about 3500 too.