2 strokes

[Mark_Able]

Does adjusting the air screw make any difference? If not, then I think you've got an air leak somewhere. As said, probably carb rubbers... :

[crewy]

Does sound like an air leak to me, i had this on a aprilia rs125 i bought on the cheap, the problem was not enough compression in the chamber, once i had replaced the crank seals it worked fine.

Electrical side of things, have u gapped and cleaned the tdc sensor on the ignition unit?

Other then that only other thing i can think it could be is the exhaust chamber, or exhaust can filled up with carbon waste?

[alanTDM]

last night rerouted the throttle cable under tank took top off carb easier from that end found carb slide wet mmm dont think that is right.anyhow replaced it back on. Started second kick got it to idle ok but when engine started to get warm it cut out then started the process all over again so back to start again 1st post
Also:-
Air mixture screw does alter the engine speed when in or out got that so when opened throttle quick there was no delay or bogging so i know thats ok. with the slide wet im now wondering if the float needle and seat seal properly it may be that is the problem as the wet slide is neat petrol.
this is turning out to be a trial of Logic and deduction ill get there in the end

[Cemorah]

The slide will be wet once run as air in carb gets blown forward and Back and will "blow" past the slide this is normal If it starts to bog once warm it is likely to be running rich also as the air screw does nothing this sort of confirms it.

1 Is the centre electrode of the spark plug a mousey brown or grey? I suspect it will be sooty black confirming rich running again.

2 When you checked the float height by turning the carb upside down did you set the float height as the little tab JUST touces the pin on the valve or did you do it with the float resting on the valve? If you did the second you have probably set you float height wrong causing an overly rich mixture.

3 Check the float needle is fully cutting off the fuel during its travel If not clean float needle & valve thoroughly and recheck before starting engine.

4 If all this is correct ensure the air bleed circuit and pilot jet are clear (an airline is good for this.)

5 Finally check all you jets: Main jet, emulsion tube, pilot jet, slide and needle are all correct for the bike - people have a habit of jetting up thinking more fuel is more power with disatrous consequences on 2 strokes:---

NB Modern 2 strokes usually pump oil into the carb which is then sucked into the engine to lube it. Running them rich of fuel can wash the oil out of the engine causing failure usually of the big end bearing. I know this to be a fact as I have had to rebuild ny mates TZR125 recently for just this reason. Squirt some more 2T oil through the inlet before trying to start again. Better an oiled plug than an un oiled engine.

Chokes on most carbs these days are of the "excess fuel" type and only work at idle. Do not leave it on for long as the same thing can happen. Any problem or things you are not sure of please feel free to call me 07795 266230

[alanTDM]

Sunday :- The carb was cleaned out and everything is standard,the float height was checked again 20mm service limit 21mm+- 2mm.
I can adjust the airscrew to slower idle and also faster and set it so it response is instant when opening throttle quick.
Going to change the plug again cause even new ones arnt allways good.
if that does improve things then ill test the ign coil also.If they check out ok ill take a look at the reeds,ffs friggin hell! that means the carb has to come off again Grrrrr!

[Mark_Able]

So when it cuts out (once warm), I'm assuming it turns over by hand ok? :-?

[alanTDM]

Yea the annoying thing is when it does cut out it kickstarts with no problem at all

[Cemorah]

Is it worth putting a timing light on it to see if there is a spark as it dies? got one if you want to borrow it

[jonnydangerous]

check the small o-ring around the mixture screw, check its ok not perished or split, when youre starting the bike after its cut out are you twisting the throttle? this will use fule/air circuits other than the idle circuits, where as leaving it to idle will only use the idle circuit.

so, it might start ok but not idle......

how worn is the slide and carb body....search on the net, throttle problems are pretty well known on the KMX200....think ive got a KMX 125 carb somewhere if the idle screw and oring are the same...

JayDee.

[alanTDM]

checked the coil and Pickup coil wiring with multi meter all ok.Fitted a new O ring to idle screw that didnt look to healthy, there's no O ring fitted to the airscrew dosnt show it on the parts PDF.Fuel level was checked and that was ok aswell.
The 125 carb is the same size only the jets and needles are different.
I got it running on idle today at 1300rpm and was ok, going to have another look at the throttle cable in case its sticking was a bit slow in dropping its revs to 1300 but it still cut out though after blipping the throttle. >
I got a timing light and a ColourTune so going to fit that see what colour it shows the mixture, that should give me a indication of whats happening mixture wise. If i open the choke the bike looses revs like its going to stall so thats normal anyhow with hot engine.

Im getting there slowly
And to make things worse spotted my ex Yamaha TT350 i sold 5years ago, in Melksham the other day