125H runs for 5 minutes then dies

[YZ250H]

Hi guys,

Carb is definitely 4V2-00 - that's one thing I'm sure of.  I haven't had the reed block out, but will when I pull the cylinder off.  I'll also check in the crank case to make sure there isn't any moisture in there.  Also look for pinholes or pitting in cylinder/head.  I assume Boysen reeds have some sort of identifying mark???.
I don't think I put too much oil in the cylinder when I put it back together - that's 'cause I didn't put any at all  .
I had a thought that the stuff weeping from the exhaust may be moisture (from the combustion chamber via head gaskets) mixed with the carbon that was already in the exhaust 
Does the pilot jet control low or high speed operation ??  It runs loud and strong once it gets on the pipe (sounds very much like Hilly's 100) .
Boney has opened a whole new can of worms with the crank seals.  From what I could tell they seemed to be new as they still had all the texturing on them and where sealed with the same sealant as the cases.  I assume this had not been done that long ago - maybe when they put in the new piston and rings .  The seal on the ignition side was a tiny bit crooked - only a poofteenth.  I will keep trying the spark when she dies to satisfy myself  (and you guys) that it isn't a spark problem.
I checked the float level last time, but will do it again when I've got the carby off.  Is there a particular point to measure it at.  I have a Clymer manual and have been following that closely (when I can work out which bloody model they are talking about).
I'll try the carb jets etc, lap the head and cylinder, check the reeds are yamaha.  Then it may be down to more serious business as Boney suggests.  If I have to pull it down again I will get Mr Yamaha to put it back together this time just to be sure.
I'm with Boney on this one.  I think we are getting closer.

[BONEHEAD]

wow wow wow , sealant on the crankseals, did you happen to check the gearbox side crankseal as this is the one that lets oil in the crank area when it is worn or put in the wrong way or if sealant is used to try and mask a concern temporarily, normally when just doing rings you dont have to strip down the cases unless you have had a major failure, so i take it that this engine was semi assembled or was slapped together by the previous owner who bought some no more gaps and said this will do for 5 mins of fun,i think you need to inspect the crankseals i believe its sucking in gearbox oil and killing it. cheers BONEHEAD

[DJRacing]

Yeah Bonehead (wow wow wow) I agree. It sounds like the crank seals aint the best if sealant has been used to hold them in place.
The pilot jet is for first eighth throttle. On the reeds just make sure they arent broken and that they are closed and not sticking up.
The crank seals can be replaced without splitting the cases. And when you replace the barrel, make the piston go fully down and check that it has opened up the transfer ports fully(if not you will need to put a thicker base gasket in) and then move the piston to the top of the barrel to check the hieght. Then back the piston down about 5mm and get to little pieces of solder(about 10mm long) and put them on top of the piston(from the cylinder wall inwards at opposite sides of the piston). Bolt the head on and slowly crank the piston over so the it goes through top dead centre. Dont crank it over fully or the little pieces of solder will fall in the crankcases. Remove the head and get the 2 pieces of solder and measure the flatten parts. This is an easy way of measuring the squash band. It should be greater than 1.1mm-1.2mm. This is good as it well help when timing the bike to get it to run properly. It also will aid in eliminating (pinking). anyway YZ250H good luck.

[BONEHEAD]

c mon c mon did you get the chance to test the bike over the weekend, im still keen to see what the out come of this senario is, keep us informed i want hear the good news, good news that you have found the cause or good news that we have helped in locating the concern, cheers BONEHEAD.

[YZ250H]

Sorry Boney,

No progress this week-end.  Too busy working on the farm - don't you hate it when life gets in the way of fun.   I did pull the carby off and bring it home, so after the weekend I'll know the jet sizes and float height.  After that it's down to lapping the head.  Head O rings haven't arrived yet anyway.   I think I will try the water leak theory first.  If that doesn't work I'll have to pull the motor out.  I have a minor oil seep between the cases that is annoying me, so it looks like back to square one.  I'll do the crank seals while I'm there - just to be sure.
That should solve 2 of the big theories.  If that doesn't work I'm back to the little stuff again.
Don't worry - I haven't given up on it.
One thing I neglected to tell all you blokes is it has a boost bottle fitted on a 5x5 manifold.  That may change the jetting slightly ().
I'm working on it .

[Freakshow]

delete the thread, remove all traces of your name, then list it on ebay as a fresh barn find condition unkown and forget it and buy a good Pre 75    anything with water is just 1 to many elemants.    See its all fung su.

its the cosmic triangle : metal (spark plug), air (via air filta ) and earth ( oil/ fuel) = 3 point balance, if you go adding water in there it just all gets umbalanced. 

just face it YZ, your battliing the forces of nature here, no good can come of it; 

be gone freaky bike back to your maker !  selling is the preferred over a tribal burying. ( although im sure if you took it to the DT nats they would throwit on the fire for you  )   

[BONEHEAD]

FREAKY YOUR OUT THERE IN NOWHERE LAND i beleive in the spirit of solving lifes mistries ,like why do we need motor cycles , why do we need 2 stokes , why do we need the niggly concerns, why do we need to believe we can fix them, why do we believe we have done our best , why do we believe in god why why why ? because im on holidays and had to many beers and im feeling emotional and i believe we can save this bike.IF IT DONT RUN SELL IT TO ME .

[YZ250H]

No way dude.  I won't be selling it !!  I am determined to get this bugger going.  Then I hope to race it.  If nothing else I have learnt a lot about this motor.  It will go - when it does I will post Hilly's video 

[yzhilly]

I only hope that i can still turn the computer on when you do .Hhhmmm i'm getting old

[YZ250H]

 

It's a fair cop Hilly.  It has taken me a rather long time.  Close now though.
Maybe by the time I'm finished we will be able to turn the computer on by mind control 

[BONEHEAD]

GUYS CHECK WHAT I FOUND  ,look at my post RED ALERT 125 H SOMEONE LEND ME MONEY

[YZ250H]

I'm onto it this week-end.  Plan is to remove motor and send bottom end to Mr yamaha for resealing case halves with his secret sealant (stag didn't work) and installing new crank seals.  I will lap the head (thanks Pokey) and put it back together when Mr Yamaha is finished.  Then we try again .

[yzhilly]

Stag W.T.F  I think that's for plumbers cracks mate . Anyway if you get the bottom end done properly you should be right and hopefully have running some time next year ??. C'mon Tony pull ya finger out and get this sucker running .

[YZ250H]

Ok Ok, I'm on it - Geez you nag like my missus  .  She even asked me the other day when the bike was going to be running again - apparently the 250 resto should be going faster too  .  I've had 2 week-ends at home and the bike is at the farm - poor excuse I know , but I have enjoyed being able to sit and have a beer (or two).
I should reveal wether the water has been leaking into the combustion chamber tomorrow. I will post photos if I find anything.
Got the new head gaskets (O Rings), sheet of glass, nikko pens, oil and wet and dry, so should all be ready to go back together next week-end.  I will put pressure on myself now by saying I will post a video of bike going on Monday 29th (this year  ).  Then we can officially declare this thread dead and burried

[YZ250H]

Update for anyone that GAS  .  I drained the oil and apparently while I wasn't looking someone replaced it with thickened cream.  So after all that there is water in the oil.  I swear it looked Ok when I checked it before.  What does that mean ?  I know it means a water leak, but from what I can see there are bugger all places it can get in.  Perhaps the seal on the impeller ??.  It is interesting that the barrel has a bit of a rusty film on it and you can see splash marks where the carbon from the top of the piston has splashed onto the bore.
I have checked the reed valves - all good there .  I have lapped the heads thanks pokey.  After the first round of 1200 I decided to go back to 400 as there was a bit of pitting especially on the barrel.  I'll post some photos later if anyone is interested.
So at the moment motor is out and split ready for Mr Yamaha to seal the cases for me and replace the crank seals.  Lapped head and new gaskets hopefully will be an end to my woes.
Anyone else got any suggestions as I put it back together (again)
Should I use some sort of sealant between the barrel and the head or just rely on the Orings to do all the work ?