Mikuni hsr45 on Xr650L

Hi there I have a xr650l that I have built upt to a 706CC 12 to 1 compression a megacycle cam with a stock header with an E2 muffler. I am running on cali super unleaded. I am setting up a msd programable single cylinder igntion and would like the jetting to be a little closer so it can run smoother. I am familar with tuning a FCR but not a Micky. I have tuned it on a dyno jet 250i and got a baseline. the screw is 1 3/4 out a 30 pilot a y2 needle on the richest clip and a main jet of 145. if I do a full pull the airfuel ratio looks diecent except for a lean spot of 14 at 5500rpm and then tapers down to 12.6 at 8000rpm so the dynot chart says that I need a richer needle but when I am at 1/8th to 5/8 throttle at stable speed it is reading 10 on afr and stumbling bad. so when I do a roll on pull at wot it bypasses the bad area and pulls strong. the afr previously was almost 15 on the previous run and I changed the pilot from a 40 to a 30 and it helped the torque about 1.5ftlbs. should I keep leaning out the pilot or should I order up new needles I would like to figure out which direction to go before I order needles. tank you very much

doing wot rollons on a dyno is a main jet test for the most part.

you determine pilot jet selection by idle reaction to the fuel screw and the measured a/f ratio. needle is set up via steady throttle tests.

pilot circuit is for idle and just slightly off.you should not be tuning power or response with it.

throttle response is tuned with the accelerator pump.

does the idle react to the fuel currently? idle with the fuel screw full in?

your main jet sounds alittle big still.the a/f line will never be perfectly flat with a carb.its just how it works.

your steady throttle a/f is bad becuase you trying to tune response with the needle.you need to set it for clean steady throttle running. 13.0 - 14.0 afr.

this your dyno?

yes the idle will start to stall out when the screw is 3/4 out.

so the steady throttle 1/8 to 3/4 is all needle. Have you ever heard of the hsr harley mikuni having a hard time to tune. I dont want to be chasing this thing all over and it end up not working for my motor. Yes it's Dan Gurney's dyno I just run it. like i have set up a lot of fcr but no mikuni's, thanks for your time.

correct,you tune 1/8-3/4 steady throttle with the needle. 1/8-1/4 is the straight diameter and the rest is clip position and taper.

its no harder to tune than any other cabr but tuning info and parts i no where near what a fcr is.

i think its a touch big for that motor set up.

Change of plans now.

Sudco says that the needle that is in it is the leanest that carb will go. I guess I will throw the fcr 43 onto it. I was just leaning twards the mikuni because it flows better on the flow bench. sounds like I was walking into a road of issues if i kept using it. so good bye micky.

if you have the needle in the richest position you should try leaning it to see if it comes around.clip position has a drastic effect.

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