Mild built predator 420 carb

T

trey johnson

New member
I have a mikuni sbn 38mm on the way and I wanted to know if anyone has ran them to tell me about what size jets I need to run for a good starting point and I'll just go from there.. I believe it's coming with a 65 Low and a 107 high
 
I run one on my yz250f and kx125...
I just had to adjust the high and low needles to get the AFR each engine wanted...
 
Do u know what jets are in it with the amount of adjustment these carbs have I almost feel like the 107 main and 65 pilot will work fine just have to fine tune like you said but then again I may need to go a little smaller not much
 
I would have to look it up...
The carbs came off a Polaris 750 jet ski...so what ever they came with stock, and stock pop off also.
Also I made a velocity stack and air filter adapter combo...
 
I ordered it all from bullfrog motorsport and I sent him an email of what all I had done to the motor and he it testing and jetting the carb for me so I should be pretty dang close to what I need but for now stock carb is doing fine just drilled the jet a little bit..
 
trey johnson said:
I ordered it all from bullfrog motorsport and I sent him an email of what all I had done to the motor and he it testing and jetting the carb for me so I should be pretty dang close to what I need but for now stock carb is doing fine just drilled the jet a little bit..
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"drilled" "a little bit??" ?????????
 
I have a SBN for sale. make me a reasonable offer.
 
trey johnson said:
I have a mikuni sbn 38mm on the way and I wanted to know if anyone has ran them to tell me about what size jets I need to run for a good starting point and I'll just go from there.. I believe it's coming with a 65 Low and a 107 high
Click to expand...
HI I c its a old post did you ever sort it out. And if you did what needle and pop off and jets did you end up with. And was the return block off.
 
Trey johnson has not been on since 2017 .
65 low and 107 high is what it states , are you close too that ?
 
flattop1 said:
Trey johnson has not been on since 2017 .
65 low and 107 high is what it states , are you close too that ?
Click to expand...
Thanx for the reply. I'll check Tom getting new kit Tom. Pop off you said around 15.going to change the needle to a 2mm also. Some people block the return pyp. Should it stay open and must the tank have a vent valve or just a breather.
 
Yes i still have the carbs. Give me your number and i'll send you some pictures,
 
Method racing said:
Thanx for the reply. I'll check Tom getting new kit Tom. Pop off you said around 15.going to change the needle to a 2mm also. Some people block the return pyp. Should it stay open and must the tank have a vent valve or just a breather.
Click to expand...
Never ran one . Vent valve as in roll over valve ? Either should function the same . The breating ability needs to be equal or greater then the fuel comsumed .
Return it seems different for every one . Using a kart style pump i would try it with it blocked off . Even connect a pressure gauge there too see if its over pop off pressure . If you run it i believe you need a restriction in it .
I can only assume bigger then the main jet or equivalent.
 
flattop1 said:
Never ran one . Vent valve as in roll over valve ? Either should function the same . The breating ability needs to be equal or greater then the fuel comsumed .
Return it seems different for every one . Using a kart style pump i would try it with it blocked off . Even connect a pressure gauge there too see if its over pop off pressure . If you run it i believe you need a restriction in it .
I can only assume bigger then the main jet or equivalent.
Click to expand...
Sbn may have an out pressure port(s) to feed other carbs without pump stacks. Those would need plugged, I believe.
 
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