carb kit changes tune?

rossthaboss11

rossthaboss11

Location
CT
ive had my ski out running fine and i put in a new carb kit yesturday. i took it out today and the tune was wayyyyyyyyyy off. its a single 46mm mikuni wetjet carb for my superjet and my low speed was at 1/2 turn out tuned pretty well. it kept bogging down and acting like it had no fuel so i richened up the low speed. the top end was mint. as i richened it up it got better and better but still not awsome. i found it all the way at 2 turns out and still not good yet. as i was riding it shut off and my rings/cylinder fried (to lean). compression was 25psi in the front cylinder. do new carb kits restrict fuel more or something?
 
Matt_E

Matt_E

steals hub caps from cars
Site Supporter
Location
at peace
What's the jetting? (Main, pilot, needle & seat, spring, popoff)?

The lo adjuster adjusts idle mixture only, while the hi adjuster adjusts top end mix only.
For everything in between, you need to adjust the items mentioned above.
You can't just throw a carb on a motor and expect to tune it with the adjusters alone.
 
S

sflsurfrider

matt, he said that it was running fine until he put a rebuild kit on the carb.

like mcdog asked, did you change the spring?

they should really update the instruction sheet that comes with the rebuild kit to accommodate 44's that use the orings that it says "for 38mm carbs only" for.

if this is your first carb rebuild, you may have not done it right. you can take it apart, and take a pic one diaphragm and plate at a time, and maybe we will see what went wrong.
 
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rossthaboss11

rossthaboss11

Location
CT
i didnt change the spring and i put the jets back in the same exact spot. i did notice that the 38,44,and 46's were all a little different and i was confused so i put it back together the same exact way i took it apart. it idled fine from the beginning and top end fine but when i would punch it it lagged alot. and as i richened it up that symptom cleared up but it wasnt as snappy as it should be then it blew b4 i could turn it out more. im running a 127.5 low speed (which was at 1/2 turn out) and a 150 main which is at 2.5 turns out. i forget what the needle and seat were i believe 2. something not sure. and not sure which spring. i dont have a pop off gauge either. i didnt change anything except the new parts of the carb kit.
 
rossthaboss11

rossthaboss11

Location
CT
its a 701cc bored to 733cc with a head at 180 psi, msd, prop, single 46mm carb, riva red pipe, intake and maybe a couple other mods.
 
Matt_E

Matt_E

steals hub caps from cars
Site Supporter
Location
at peace
Sorry, I misunderstood. I thought you'd put a whole new carb on it. :)

You might go to Mikuni's website and download the SBN manual. They have pretty good exploded views of the carb(s) in there that would probably help you.
 
SUPERTUNE

SUPERTUNE

Race Gas Rules
Location
Clearwater Fl.
I did a quick search (I knew I saw it somewhere) and came up with this...
http://www.x-h2o.com/threads/...mikuni+springs

You might be running a main jet too small for a Riva red pipe, I'm thinking that I ran somewhere around a 160-170 main jet. You should be running no more than 1 3/4 turns out on the high adjuster screw.
You also might have raised the pop-off a little by replacing the old float arm for a new one and could have little more pop-off which leans out the carb jetting.
 
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rossthaboss11

rossthaboss11

Location
CT
supertune the link does not work. but thanks for searching for me. i do have a 160 jet and tried that but it was to big. ill have to go get a 155 and try that. was your 160-170 with a 44mm or 46mm?
 
rossthaboss11

rossthaboss11

Location
CT
also when i blew up the motor wasnt even that hot. was this only because the low speed was lean? i was doing some tail stands when it happened. i figured the whole motor doesnt get that hot maybe from low speed but the internals can
 
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