2 strokes

[alanTDM]

Anybody on here know the ins and outs of 2stroke engines?
Just rebuilt and got bike started 2nd kick but cuts out after a few mins after revs increase :( Starts again ok but then still cuts out.

[Mark_Able]

Any noises when it cuts out? Could be being starved of 2 stroke oil? ::)

[jimmer]

Starved off petrol the revs will rise when it trys to get fuel could be blocked fuel pipe breather in tank.

[jj]

check for air leaks on inlet rubbers or exhaust

[finbar]

Yes...lots! [smiley=thumbsup.gif]

[crewy]

Could be the main jet blocked with a bit of crap, the air adjuster screw on the carb might need some tweaking, has it got a rave valve? they get a bit seized up and dont open. What engine is it on?

[Scotty]

Start with the basics, next time it cuts out, turn the fuel off immediately and crack the drain screw on the float bowl to see if there's any fuel in the carb - could be blocked fuel tap or filter, maybe the needle valve needs checking. Check for air leaks, reed valves sticking or broken.. you say just rebuilt - did that include crank seals? :-?

[Bennett]

Mine raises, however, it doesn't die again, but only sometimes.
Something to do with the carb? Check it. :)
BTW, I am no expert, I've been riding since last October. :D

[alanTDM]

This is a Kawasaki KMX200
The engine was stripped,new crankseals new piston and rings,all gaskets are new ,power valves are spot less carb was stripped and cleaned ,new air jet cause old one was to big ,float height is now with in tolerance 21mm-23mm.Reeds and block ok cant see any sign of cracks on the inlet rubbers and air cleaner is new.
checked the petrol in the bowl all ok and from what i can tell choke is working ok aswell.
sometimes does not always slow down from 3k rpm quick either when you shut the throttle off and when it does hit idle it cuts out.Air jet screw is set at 1/1/2 turns out tried it in various positions.
the way it cuts out would seem to be electrical rather than a fuel prob checked kill switch aswell thats ok and side stand switch in fact anything i an think of.

[Jon_W]

Sounds like the carbs are gummed.... The only electrical thing that would even come close to these symptoms is a cdi sensor fault...

I had this with the Honda when I last started it after a lay up. Just kept running it till the carbs cleared.

Are you getting big clouds of black smoke? Sounds like carburation...

[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 :(

[jonnydangerous]

il dig out the carb if its any good for spares, swap it for a burger and chips... :-)

[alanTDM]

il dig out the carb if its any good for spares, swap it for a burger and chips... :-)
Okies thats a deal ,Iv made some progress :)but iv come to a halt at the mo due to ****e weather as i got no garage.
Sent you a PM

[alanTDM]

Problem sorted now it was electrical took flywheel off and stator and found 2 wires which had cracks in them and were shorting out.Could only see the open cracks if the wires were bent slightly which must of been happening when it was fitted in situ.

[BB]

Good to hear you er 'cracked it' Alan! :D

BB

[alanTDM]

Good to hear you er 'cracked it' Alan! :D

BB

Yea thanks BB all is ok its fixed and engine is running as normal now