SX/SXi/SXi Pro need some mikuni help

[SterlingSilva]

ok well here are the specs...

750 w stock dual mikunis
factory pipe
k&n flame arrestors

carbs were recently rebuilt
75 low jet @ 1.5 turns out
147.5 high jet @ 1 turn out

needle is a 1.5 according to the stamp on the seat (stock?)
spring is either faded gold or dull silver (stock?) replaced with same when rebuilt

ski runs good... idles no prob... mid n top end good
low end is usually ok but occasionally get a bog/hesitation on the bottom end just off idle.
usually i feather the gas just to keep it alive n eventually it clears up.

thinkin im getting a lean condition caused by high pop-off due to the k&n f/a. i wanted to run the stock f/a to confirm this but it wont clear the factory pipe.

so my question is.... what is stock sxi dual mikuni spring and needle and if anybody can suggest anything id much appreciate it.
my plan is to try a spring one step lower and see what happens

the top spring is whats in the carbs now. the botom and middle are what came with the rebuild kit. i think top and bottom are the same



thanks
Eric

 

[SterlingSilva]

ok... i have an update but unfortunately no good news. on the contrary somewhat baffling

so i decided i was gonna check the pop-off before ordering new springs.
i wanted a basis for comparison so I did a little research and found out that most people are having good results with around 30psi.
also found out that the original mikuni rebuild kits (what i used) comes with 115 and 65 gram springs.

therefore the springs in my carbs should be gold 115 gram springs and with a 1.5 needle should be in the 55 psi ballpark.

heres the twist...

i setup and checked the pop-off pressure and im getting about 13 psi!!!! wtf!!
im using a fork shock pump with only 10psi tick marks that i adapted but i had no air leaks until the needle released and both carbs read nearly the same pressure.

so how is this possible? the ski runs great for the most part and the issues im having are textbook high pop-off.

I swapped in the longer shiny springs that i believe are 65 gram just to see and i got just over 35 psi on both carbs. This seems a bit high but is much closer to what mikuni claims it should be (32psi)

what to do now? :shrug:

 

[SterlingSilva]

found a mikuni 95 gm spring i had (was able to identify it because its wound reverse from the others) and tried that and i got about 27psi

this makes no sense!! :/

also kinda curious why the 95 and 65 gm springs are longer than the 115 gm spring that came stock

hope somebody can help

thanks

 

[88kawi5fiddy]

are your main jets even big enough? my mains with a factory pipe are 172 front 170 rear.

edit: im running 42's but the stock ?38's? should still be higher than 147.

 

[PLD]

Ok so there was no change in your bog with those 3 different pop off pressures? Or have you just been bench testing to see?

 

[SterlingSilva]

carbs are stock as are the high jets. low jets have been changed from 67.5 stock.

ive only been bench testing but cant fathom how im getting the pressures im getting.

considered increasing my low jet one step and leaving the spring the same n see how it runs.

crazy thing is that the symptoms ive described in my first post sometimes will not even happen on a ride at all

thanks for the response fellas