Engine Goes Lean at Mid Range

I just intalled a bored carb and Alba pipe and an A/F Ratio meter.  I got the jetting set to 13.5 at idle and 13.3 to 13.8 at WOT she seems to be running great.  While we were out riding the rhino when decelerating, going down hills, or running slow she would  go super lean, 22.5,  and often backfire, sputter and sometimes die.  I'm running with the airbox lid removed and a Uni filter.  I tryed it with the airbox lid back on, 2004 style, and it seemed a little better but not totally.  I'm running a 155 main, 45 pilot at 1.5 turns out.  When I was originally tuning it I had a 50 pilot and to get 13.5 at idle the af screw was at .5 turns so I went back with the 45 pilot.  I'm operating at 9200'. The lean scared the shit out of me so any suggestions would be greatly appreciated.  Thanks everyone!!

valve lash is very important on how well the fuel pump works at low rpms

Thanks James I will check the valves first thing next weekend.

Scott, when You get it ironed out, let me know how You like the Alba bored carb and Alba pipe combo. That is exactly what I want to do to 07 660.

WV Hot Rod Rhino wrote:

valve lash is very important on how well the fuel pump works at low rpms

would be true still if you have an electric fuel pump.  mine sometimes leans out every now and then a mid rpms.

not with electric.....if it has a dynojet needle get it out

WV Hot Rod Rhino wrote:

not with electric.....if it has a dynojet needle get it out

im not sure if it does I will check that out though..  any word on my order?

I'll get back Larry, no dynojet here.

Okay I adjusted the valves, they were a little loose but not bad at all.  It still goes lean. It doesn't do it all the time. When it's running good, not going lean, when decelerating it goes lean for a second right when you let off the gas and it richens up once it's idleing.  I put my airbox lid back on and it still does it.  I richened up the idle and it still does it.  I even tried a different carbureator with no change.  It seems to be worse when it gets hot and we are cruising slow and then go down a hill where the engine is braking.  It goes lean and pegs out the A/F guage, backfires and sometimes dies.  Next?  fuel pump, or plug maybe?  I'm starting to scratch my head.  But other than this the pipe and bored carb make a huge difference with power.

If it done the same thing with a different carb, I would think it's fuel pump.

I would suggest an Alba high output fuel pump if You don't have one already. I also use Weller racing clear fuel line kit that allows the use of both outlets on a high output pump.

yep..get a new pump

when you get straight give us your input on that carb mod very interested thanks and good luck

Try to get the idle set at 12.5,check float level,make sure that the washers are on the needle right,also take the thick metal washer that's on top of the needle and try it on the bottom,the bored carb will need a bigger pilot....13.5 at idle is too lean,so when you let off the gas its pulling off the pilot jet and it goes lean and will backfire and pop,may need a 55-60 pilot,also about 13.2 wot is where u want to be, 13.8 -14 is too lean and you could get some spark knocking and ruin your piston and rings and cause some overheating. Hope this helps