100:1 Mix

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LS614

Active Member
Dec 22, 2009
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I had to adjust for my mix too, I'm running the sbp expansion chamber and the dax gtr50r carb, both which use more fuel, and I still needed to change the jet from .75 to .70 to keep from four stroking. It's all pretty easy fixes though to get the powerband perfect! Now all I worry about with my HT is snapping the keys on the chain side sprocket dnut
 

LS614

Active Member
Dec 22, 2009
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My goes ZOOOOOM instead of Braaaaaaaap all the way from idle to top speed, that's what you wanna shoot for. No 4 stroking, just the pure dirtbike kind of sound (2 stroke dirtbike that is ) :D
 

Don P

Member
Sep 1, 2010
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indiana
thats what i am shooting for ZOOOOOM instead of Braaaaaaaap. i am beginning to think this nt carb is a pice of !#$$^***(*%$$%&^&**(((((((( translate crap lol i can't seem to find the sweet spot. i think it is MIKUNI TIME!!!
 

LS614

Active Member
Dec 22, 2009
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Don, if you get an expansion chamber and the RT carb from dax you'll be set. The RT carb is GREAT for me, I love it! It is monster torque, good quality, and way cheaper than the mikuni!
 

mapbike

Well-Known Member
Mar 14, 2010
5,502
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Central Area of Texas
thats what i am shooting for ZOOOOOM instead of Braaaaaaaap. i am beginning to think this nt carb is a pice of !#$$^***(*%$$%&^&**(((((((( translate crap lol i can't seem to find the sweet spot. i think it is MIKUNI TIME!!!
Take the jet out of that NT solder it up and redrill it with a #73 wire gauge bit and put the clip on the metering needle second notch from the top and I'll bet you see a big difference in how it runs, just do the good ole plug check to make sure you aint to lean.......

Peace
 

LS614

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Dec 22, 2009
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Great advice mapbike, and just to clarify to those who never rejetted, there is a HUGE difference between a #73 and a .73mm jet, so be sure you understand what you are doing :)
 

Don P

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Sep 1, 2010
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maybe but i got a bud that has a bunch of 18mm MIKUNI clamp ons from 50cc and 80 cc dirtbikes. i bet i can get one dirt cheap maybe free lol
 

Don P

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Sep 1, 2010
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indiana
mapbike i have been through every number drill from 70 to 74 and ever step on needle and will not stop 4 stroking #73 with top groove on needle gives me best running but still 4 strokes if not in it hard
 

LS614

Active Member
Dec 22, 2009
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I really think an expansion chamber smooths these problems out a lot, it makes the engine suck in fuel better and requires richer jetting :)
 

Don P

Member
Sep 1, 2010
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indiana
i agree with you that the expansion chamber is needed to smooth this thing out. but it will be a week or two before i can get one low on FRN Federal Reserve Notes.
 

mapbike

Well-Known Member
Mar 14, 2010
5,502
109
63
Central Area of Texas
Yes LS614 is right on about the expansion chamber or just a good free flowing exhaust period, it make no difference what you are putting into the engine if you cant get it out just as good so it can breath properly, you may even try a # 74 bit and just play with the needle to find that sweet spot, my engine 4 stroke just a bit unless under a slight load, I know some say they have zero 4stroking and that might be true, but I have had mine in the NO 4 Stroking Zone as well and they ran to hot and thus to lean so I richened them back up a bit, I ride 7-8 miles at WOT sometimes and if an engine is running lean it will cook down running like that so I dont mind the slight braaaaaaap at low speed and no load, I still get 41mph WOT with no wind, very flat ground on a good day and 36-38 mph at will wit a very comfortable cruise speed of 30-32mph with no 45 stroking at this speed.

I have manic intakes on mine and free flowing exhaust, the exhaust makes the biggest difference of all on these engines in my experience when it comes to instant noticable improvement in the way they run and pull hills.

Good luck and get a better exhaust asap and then along with the carb. tuning you will see a nice difference..........

without higher compression and a very good exhaust, I cant see the 18mm Mikuni carb doing very well on these engines, you will need to mix a good bit of fuel with that volume of air flow that 18mm will give you which may just be a bit much for the china girl, some fellas have got 45+mph using a well tuned NT carb. and a few other goodies, but I have been wrong a gillion times before too! so I say give it a shot and let us know what you nd up with.....

Peace



i agree with you that the expansion chamber is needed to smooth this thing out. but it will be a week or two before i can get one low on FRN Federal Reserve Notes.