The bike is new (2015) done around 3,000 miles.  From the get go it backfired when closing the throttle and when switching off.  Did the idle mixture mod and the backfiring only occurs occasionally.  The bike goes well, good acceleration and smooth at high throttle openings.  The problem is at low throttle settings (30 - 40 mph) it seems to "hunt" and does not run smoothly.  I have checked the vacuum petcock and it seems OK.  We are pretty much at sea level here so I am guessing a larger pilot jet might be in order.  Any advice on where to get jets and by how much to change the size?
Geoff    

As above a 47.5 is stock a 50 is the next step up . If this doesn't seem to help and the motor 's still "hunting" it is running lean and you need to do the needle jet spacer mod. seeing your at sea level I'd replace the stock spacer with 3 #4machine washers (.75 mm ,the stock being 1mm)this should make your mixture richer and solve the problem .You should adjust your air screw after any of these mods.If it still hunts take out one more washer moving to .50mm .Next the main jet (stock145) to 147.5 if needed.

HefyJefy wrote on 07/06/16 at 15:53:48:


That is outside of the range that is controlled by the pilot jet.  As batman said.....you need to raise the slide needle slightly to get more fuel in the mixture as the slide is opening.  Remove the white spacer at the top of the slide needle, and replace it with 3 washers that are #4 machine screw size.  If there is still a hesitation....remove 1 more washer and go with 2 on the top of the needle.

I would start with a #50 pilot and # 150 main....and the washer mod.  Those changes should get you in the ballpark and make the bike run better.

YES! THE JETS ARE MUCH SMALLER DUE TO CAILF. EMISSIONS!I'd check what you have and move up from there(your main may only be a 125 as I recall)(the numbers are stamped on the base of the jet) but moving the jet needle with three/two washers is standard to all carbs.(see technical section fuel&exhaust stock carbs&jetting,casb specs) your jets are 47.5 pilot 125 main.Dave's 50/150 is right on your bike will run completely different (very well)

I hope 125 is wrong! I can't see the engine even running that lean.


Dave, when you tuned your bike with an A/F meter, did you happen to notice the AFR with stock jets? I'm just curious how lean Suzuki considered "just right".
/off topic

OK well...
I just got both the Pilot and Main Jet out, the pilot is 52.5 and the Main is 145. Not what I was expecting, however I think a 150 main might be a good move.
In case anyone is following this the bike was a new California model last year, stock.  It had the initial service (done by the dealer) and I did the 3,000 mile.
The problem has I think, been around from the start but the bike belongs to my wife so I only just got my sticky fingers on it.
I will report back once I have changed the main.
Geoff

Dave wrote on 07/08/16 at 11:35:46:


Main jet feeds the needle jet, so increasing it increases the whole range.

I'm with dave! be careful ! All the screws on and in the carb are jis (Japanese industrial standard) a Phillips head screwdriver wont fit deep into the slots unless the point is blunted,and may strip them! it's best to pick up some jis anyway.