125H runs for 5 minutes then dies

[YZ250H]

Thanks CG - I'm onto it.  Even if it turns out not to be the coil it doesn't hurt to have a spare hanging around.

You are the ebay master - Cheers

[pokey]

white smoke =Not good.
 you my son have a water leak plain and simple.
 fix that with a new gasket and a lapped head and barrel and I kind of think all your  woes  will be gone

[YZ250H]

I will investigate Pokey - thanks.  I struggle to find what else it might be, so you just could have it.
I'd still like to find out how to work out the pilot jet size.  Will order some new gaskets.  What is involved in lapping the head and barrel (and don't say running around it 3 times - I could see that coming from someone on here)

[pokey]

Bugger stole my line


 seeing as the steering head has water  issues with corrossion and what not  it stands to reason the other journals would do aswell. the  tell tale is that white smoke. water plus exhaust gases  make white smoke that can only come from the combustion chamber so as the queen of hearts said"Off with its head"

 Lapping isnt hard just labourious.
 grab a a nice sheet of float glass( an oldhouse window will do) as its a smooth flat surface, an also a sheet or several  of fine grade wet and dry  paper (start with 1200 then go to 1500 or higher) and some oil.
 Now make slow figure 8's with the head. add oil to the job to flush the build up of crap away . in about an hour you should have a nice flat smooth surface ..Take your time .
 Next do the barrel but you will need to remove the studs. wash with warm soapy water after the job is done  to remove any crap in the barrel or transfers

 if you dont feel like doing that put it into a machine shop   for the work.
 Its not hard just time consuming.

 do check the surfaces  with bluing ink  to make sure  they are flat. I use a texta  with the same results cept it dont look as flash as the blue.

 To check the main jet  just whip the bowl off the carb and  have a look at it, is a number stamped into the jet.

[Freakshow]

I'd still like to find out how to work out the pilot jet size.  Will order some new gaskets. 

the pilot is the little jet not the big one, undo the float bowl and you will see a little brass end with a flat blade  head on it, it willbe reccessed so you need the right sized screw driver to fit down in the hole to reach it. It will undo anticlockwise, the # number will be stamped on the side if its genuine it will be like a little tube with a hole i the top, a thread then a few holes in its side.  youll figure it out.  while you have the carby in your hand remove the main jet, slider , needle - and write down every number from them in your race diary.  

If you dont have a note book for each bike start one, every time you do somthing on that bike write it in, you change the rings, turn a screw in our out, every time you ride it write it down, how it handled, what the wether was like every thing, even how long it took you to get to the track.  If you do that you will never be late, you will never be unprepared, and you will never not no what set up you should have or currently have on the bike TODAY. 

[DJRacing]

250H the standard pilot jet is #80 and the air screw should be 1.5 turns out and the needle is a 6F21 clip position middle(3). The main jet is a 340 and the needle jet is a P8.

[YZ250H]

Consider both of those jobs done boys.  I will report back after the week-end on the jet numbers.  The lapping may take a bit longer by the sound of it, but I'll give it a go.
Pokey I assume you put the wet and dry on the sheet of glass between the head and the glass  .  To check the flatness (pretty sure that's not actually a word) do you put the nikko pen on the head and then rub it on the sheet of paper.  Any low bits still have nikko on them.  Is that the idea ??
Freaky, the note book idea is excellent - especially when your memory is like mine (again, old age taking over )
Thanks for spending the time on a newbie wannabe.  I'm sure there will be heaps of other people getting a lot out of this too.
Cheers

[pokey]

Thats  affirmative on all counts YZ250H, "IF" either of the surfaces show pitting  get them machined or you will be thier lapping for a week. Take your time and slow figure 8's

 good onya for givin it a go.

[DJRacing]

250H if it is a leaky head gasket (o-ring) the piston will probably look very clean like it has been waterblasted, there probably wont be any carbon build up on the top of it and will look shiney.

[yzhilly]

You should be able to check for a top end leak with a compression tester  . If it's leaking water into the cylinder it could be corroded through the cylinder  ,but if it was your crankcase would fill up with coolant when not running .

[Hoony]

 Lapping isnt hard just labourious.
 grab a a nice sheet of float glass( an oldhouse window will do) as its a smooth flat surface, an also a sheet or several  of fine grade wet and dry  paper (start with 1200 then go to 1500 or higher) and some oil.
 Now make slow figure 8's with the head. add oil to the job to flush the build up of crap away . in about an hour you should have a nice flat smooth surface ..Take your time .
 Next do the barrel but you will need to remove the studs. wash with warm soapy water after the job is done  to remove any crap in the barrel or transfers

 

Pokey that's good info, you should add this to resto Tips

[YZ250H]

As far as I can tell it all looked pretty good when I put it back together - piston and rings were new.  My father inlaw who used to be a diesel fitter suggested I grease the o rings before installing them.  I thought that was a bit odd at the time, but who am I to argue with the old codger.  The surfaces of the bore, head and cylinder looked to be Ok, but you can't tell by looks obviously.  Soooo - I'm making the hit prediction that it may be as DJ suggests.  New orings are ordered and I'll do the flatness test to make sure.  The do probably the only lapping I'll ever do in my life 

Hoony, IMHO all the stuff on here is gold.

[Freakshow]

 geeze #80 sounds a big pilot, these things cant run the old Mukuni vm's then, they on a  kehin or some kinda pumpa ? what i would have thought would be under #45  , but then i know nothing about anything from 75 - 85

i Was MIA that whole time.     

One minute i had  a 125 elsinore ---> the next time, i sat on somthing i had a xr250f and a Rz250R.   

did'nt realise they made bikes in those years     eeeeek

[BONEHEAD]

jesus a #80 pilot jet my mates yz 250 h had that as a pilot and it would run and die, i believe thats far too big for your 125 , is the carby for your modle or did you source it somewhere else?, i dont believe its coolant entering the cylinder as you are not experiencing a missfire, if it is blowing white smoke on restarting the bastard you may have a leaking crank seal or a seal in back to front and is sucking oil in from the gear box,you may even have a worn area where the seal runs on the crankshaft allowing oil to enter the cylinder and causing the spark  to go out . how long has it been since the rebuild ,have you put to much oil down the bore when assembling , this can cause also the same effect as a leaking crank seal, if you are sure the spark is good then i believe you , if you run the bike on a stand will it die or only when the bike is under load, we are getting closer to resolving this concern , white smoke strange smell could be a clue. cheers BONEHEAD

[DJRacing]

The way 250H explains the way he has to start the bike,(choke on and full throttle) tells me that his pilot jet is to small(maybe a 60) which is what a YZ125G runs as standard. I have always found that the standard yammie settings are pretty close. If the carb on the bike has 4V2-00 on it then it is the correct carb. If he is running boysen reeds the standard setting maybe to rich but it doesnt sound like that to me. Yeah Bonehead a YZ250H does run a 80 pilot but the slide cut-away is 3 and the needle jet is a Q-0 and needle 6F16. All this is in a 38mm carb not a 34mm as the 125H. The float level for the YZ125H should be 23.4mm
I can understand suzuki boys thinking that an 80 pilot jet is huge because they seem to run 30-45 pilots but, they also run different needles etc.

But anyway, if there is another problem (leaky head gasket or something else) the pilot jet wont be to much of a concern untill the main problem is resolved.