bike splutters at high speed

[jackliveshere]

i have an atomic pro x 125 which was running pretty poorly out of the box but i seem to have solved a few issues. adjusted valves, got a decent air filter, reemed out my main jet til my plug is running a tan colour (was white to start with) until i can chase up some new jets. have my needle on the richest setting though i know this needs correcting when i get a bigger jet and have my fuel mixture screw out 2 turns. the bike now runs well on a tight track and feels good but it lacks the bottom end punch of my mates which is a wheelie machine (but helps me slide through corners instead of battling to keep weight on the front wheel) and the main problem now is when i test it on a long straight it pulls well til u r revving it out in top gear close to maximum speed and then develops a splutter but if u back off and throttle it again it clears for a lil bit and then misses again. i was originally thinking it was struggling for fuel so i removed the fuel filter which didnt fix it and now i am not so sure especially as the plug is looking good. have cleaned carb many times (26mm mikuni) with no benefit. anyone got any ideas or had this problem before???

 

[tfmartin]

I am having the same prob with on of my agb 29's, but only after i changed gearing on the sprockets, I think I am hitting the rev limiter but I'm not positive, I am looking at an aftermarket one and will let you know if that corrects it.

 

[HardaFasta]

Let it breathe properly.You have described that you have her running rich to very rich.
Now increasing the carb size (aka:throat or choke size) does nought,unless your engine is capable.Stock engine,needle clip should be central to one clip down for a pod.3/4 of a screw out on the mix.Float hieght should be 1-2mm above stock.
Increase the concentration on the timing factor and then you might start to get what your lookin for

 

[HardaFasta]

Heard heaps about 26mm Mikuni`s on them bikes.Not one of them that uses one and runs like a dog shot in the arse is stock.Port,polish,map,timing,ignition,h/comp engine,valves,springs,cam,balanced,etc
Before you work out how fast you wanna go,work out your budget.
Rule of thumb....go as fast as your wallet

 

[jackliveshere]

firstly the budget for the bike is minimal as i just bought it for the kids but i like to have a play now and then so not looking for a stinker, just a bike that runs sweet. i hate my machinery not running right. carb is the stock item which came with bike and it was running way lean out the crate and was really gutless. i changed the needle first as i had no spare jets and then just reamed the main jet out to go up a few sizes (stock jet was 56, way too small). do u know what main jet sizes are good for stock motors for maximum performance without overkill?? also hardafasta u say 3/4 of a turn on the fuel mixture screw?? most of the threads i`ve read say 1 1/2 to 2 1/2 turns out... did u mean 1 3/4?? also u mention the timing, i`ve only played with 2 strokes before so what should i do and how?? thanx

 

[jackliveshere]

I am having the same prob with on of my agb 29's, but only after i changed gearing on the sprockets, I think I am hitting the rev limiter but I'm not positive, I am looking at an aftermarket one and will let you know if that corrects it.

i hear alot of mention about these agb 29`s, what are these bikes exactly, the atomic version of the pit pro bikes?? mine is the atomik pro x type with the twin spar alloy frame, do u know what else these are known as because no one ever refers to them

 

[jackliveshere]

tfmartin what did u do to your sprockets, the 17/37 combo?? mine are still stock not sure about front but back is 43 T

 

[johnnie5]

when the bike stutters , is it a rapid tatatatata sounds

if so then its the rev limit

if you have a nice tan colour on the plug then its sounding good

the mixture screw affects the bottom end , there is no rule that it must be x turns out its all trial and error

what you need to do is ride the bike warm and then adjust the screw

1 listen carefully to the idle speed
2 screw the mixture scew clockwise listening for the motor speed to drop off , note the position
3 screw the screw out , the revs pickup , keep screwing till revs drop off , note the position
4 screw the screw back inbetween position 2 and 3 for max revs

all done

there is some other tuning tecniques here

I'm not sure if its an air screw or fuel screw it depends on where the screw is , if its on the air filter side of the carb its an air screw, if its on the engine side of the carb its a fuel screw

if the screw is set less that 1 turn out or more than 3 turns out then a pilot jet change is beneficial , 1 size bigger or smaller depending on wwhich way and if its an air screw or fuel screw

 

[Power Man]

lol ive used this pic atleast 2 times on other threads.

to get your bike running correctly do what jonnie suggests , get your bike on idle , twist the air/fuel screw out and in, untill you hear the highest rev , and thats what it runs best on , so ive heard

this will just give you an idea of what is used at specific RPM's

Happy Riding

 

[jackliveshere]

it`s a bit difficult to adjust on the run coz its the stupid design where the screw is on the underside of the carb and is near impossible to get at while running. and nah it doesnt sound like a rev limiter... i`ll do sum more trial and error and see what i can find...

 

[jackliveshere]

i`ve jetted my banshee and my yz b4 and they run sweet so have had a lil experience. the bit i dont get is it revs well and runs well at full throttle it`s just when u hold the throttle open too long like when trying to get maximum speed it dies...

 

[tfmartin]

stock sprockets were 16-43, I changed to 14-46 which gave the bike more bottom-mid, motor revs up quicker. I thought the atomic pro x 125 was the same as the agb 29 but not sure, I will have a look.

 

[jackliveshere]

tfmartin to see the bike i have look on ebay under prox (one word) 125 and u will see the atomik bike i have with the twin spar alloy frame. where did u get ur sprockets from as all the pit bike ones i`ve found dont fit it as the inside diameter is different. the inner hole on mine is much bigger. even that elstars site everyone refers to dont have anything to suit.

 

[KTMKID]

what do you guys thing about 17-39???