In a recent post roro said that he replaced the 130 air jets in his carb top with 120 items and saw significant improvements. Would somebody please explain to me what these air jets do and how will going to smaller jets effect carb operation? If something so easy to do can be beneficial, I would be very interested in giving it a go.
QBS,
Those are pilot circuit air jets. If you're running a bit lean on your pilot circuit lowering the air jet size might help off idle performance.
Excellent!! Thank you for the response. Any help I can get coming off idle, I'll take it.
The other end of that is to adjust your accelerator pump a bit if possible.
120's were standard Yamaha specs for the a Visions. I am assuming that the cooler temperatures in this country would account for the increased need of a richer mixture. The US versions seemed to use 130's which does produce a leaner condition and of course a bit better fuel economy in the warmer areas. So depending on your climate this change may improve your overall performance, but it is not noticeable in actual fact, so it will not likely address any other carburetor issues that actually affect performance.
I have a set of 120's around if you don't have easy access to them and would like to give them a try.
Thank you for the input Louie. I'll keep your kind offer in mind when I decide which way to go. Thanks again.
Louie, have you actually tried this mod or are you skeptical because it moves away from the US lean EPA factory settings?
My point of view comes from using various pilot jets from 120 up to 135 on a properly tuned Vision and I would have to say that I have not noticed any significant difference in the "seat of the pants" performance. It may improve warm-up performance in a cooler climate by using the richer 120, which is my best guess why Yamaha used this jet in their Canadian models. When I had the Keyster kits made up for the 82's we used the Canadian specs which is why they have the 120 pilots (with apologies to our American brethren).
Personally I like the higher 130-135 pilot air jets which improve gas mileage (in my opinion) and seem to work real well for me with a modified MAC (more restriction added to boost backpressure). That's my take on the the idea. It is a valid choice, but not one that I would run out the door to do, hoping for a real game changer.