carb modification - outside the box options

81 Yamaha XJ 650 discussion forum:


carb modification - outside the box options

carb modification - outside the box options 
Dan said 2011-05-13 04:10 
 
So I have been chopping up and customizing my ’81 Yamaha xj650 maxim. The giant air box is gone and I have replaced it with four individual carb air filters that mount directly onto the carburetor. However, as mentioned in a previous post, there is a lot of spitting and sputtering and backfiring which used to send fuel back into the old air box/filter. Now that the air filters are exposed, I don’t really want them filling up with fuel and starting a fire between my legs.
So my questions end up being
1) Is all the leakage just a filthy carb?
2) Because of the change in air flow going through the carbs (a lot more air at, possibly, a slower rate), must I replace the jets?
3) If so, do I go bigger or smaller than stock?
4) I have an idea to restrict airflow through the filters by creating metal sleeves that would speed up the air as it is forced through a smaller hole (make sense?) would that allow me to avoid re-jetting?
5) What does back-pressure have to do with back-firing (if anything)? I have stock exhaust on it now, but the baffles were “removed” last time it was put on its side

That seems like a lot, but I would appreciate any direction anyone could give.
Thanks
Dan 
 
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