sputtering top end

9

91vwvan

New Member
#1
#1
I did some mods on a HF clone, 22 mikuni carb and new air,

idles great, it is very quick but it dies down at full throttle, i tried adjusting the intake screw on the bottom of the carb float, but still not holding at full throttle? what should i try?
 
Strigoi

Strigoi

#2
#2
have you done anything with the main or pilot jets yet?

if it's sputtering up top, it sounds like it's not getting enough fuel.

my clone didn't run well at all with the stock jets that came in the Mikuni. i have no idea what size i'm running running now though (used bits that don't go by jet size).
 
125ccCrazy

125ccCrazy

Well-Known Member
#3
#3
try taking the top of the carb off and remove the barrel slide, there is a needle in the middle of the slide, on that needle is a C-clip, it is probably on the middle groove, take the clip off and move it down a groove and try the bike again, if the bike runs better but still not right then drop the clip another groove... By dropping the clip a groove it raises the needle which allows more fuel through the main jet...

If the bike gets better yet and still doesnt pull hard at top end without sputtering or flattening out you will need to step the main jet up a size or two and start over by placing the C clip back at the factory setting...

The air mixture screw is not for top end problems... top end problems is in the main jet circuit, the needle is off throttle to about 7/8 throttle and then the main jet takes over fully...

I'm going to say that you probably need a bigger main jet but you can try the needle settings to see if it helps any...


If it idles good then the pilot jet is okay..
 
DrGadget

DrGadget

Member
#6
#6
npatton19 said:
You might be floating the valves?
Click to expand...
Thats exactly what I was thinking,I had that problem when I full thottled my bike,I since replaced the valve springs with 18 lbs springs but I can't try it out yet cause there's just to much @#$* snow!!!When I do,I'll post my findings.
 
9

91vwvan

New Member
#7
#7
i did upgrade the springs, thanks 125cccrazy, i'll give that a try, i did have to adjust my float, could that be too low as well?
 
125ccCrazy

125ccCrazy

Well-Known Member
#8
#8
Strigoi said:
we actually slid the needle up on mine and it helped a bit. i totally forgot about doing that.
Click to expand...
that leaned the carb out as you drop the needle lower into the main jet.... It's possible his is too rich at top end.. I'd try lowering the needle clip first, it's better to go richer than lean.... If it gets worse by dropping the clip go the other way and lean the carb some..
91vwvan said:
i did upgrade the springs, thanks 125cccrazy, i'll give that a try, i did have to adjust my float, could that be too low as well?
Click to expand...
it's possible the float is to low and the carb runs out of fuel before the bowl fills up....

Do you have a fuel pump or is the gas tank higher than the carb with a good downward flow to the carb?? If you dont have a good flow to the carb you might have to go with a fuel pump to keep the bowl filled...

Pull the sparkplug out and see what color it is.... It should be a nice tan color, not white but a semi dark tan.. If it's lighter than tan it's too lean, if it's dark brown or black it's too rich...

Let us know what you find out...
 
9

91vwvan

New Member
#11
#11
getting better

I lowerd the needle clip two notches (all the way) and it made a nice difference, not perfect but much better, so i will wait for the new jets and mess with them soon.
 
9

91vwvan

New Member
#15
#15
update

Thanks again for all the help guys, I added the 120 jet today and WOW. this minibike is screamin.
it seems i went from "how can i make this runs right", to, "I better get a helmet" in one day of tinkering.
 
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