Mikuni 32mm Vm on tm250

[Freakshow]

Freakster, if it's happening at three-quarter throttle and under load, shouldn't you be leaning off the needle a notch or maybe two ? If your mainjet is in the ballpark, your needle setting is much more critical from quarter to three-quarter throttle really, worth a try before you go nuts with a pocket full of main jets. 

NAh its a bigger hit than that, the needle wont help much until he has sorted out the jets, its too much of a differance to pick up on a needle.  if its the same thing he will wind on the throttle and when its going 1/2 wide open it will die like its out of fuel, hell wind it back and it will clear and bubble along, then he'll turn it on and again it ll motor along then die again like the spark's dead and its got not fuel to keep up,  might even be rattling at this point like marbles as the ingnition/ combustions comes and goes.

its going to be flat as a tack,  he will go mental and finanly give up after he has pulled the thing apart more time than ever in its life.

If its the same problem i had this is the solution. 

what old farty didnt say was how it was before this and whether it has always been able to get on the pipe with those jets, or if it ever did propally on a track and not just his mates farm.

i have another theory and its related to unleaded fuels,  im still to be convienced unleaded octane has the same characteristics in early 2 stokes as the super leaded did, and these piston ports from my brief association with them seem to be very fussy about fuel dumps.  Without the reeds to atomise and meter the flow on a curve, the open or closed style piston ports seems to me, to now need closer scrutiny on the fuel ratios, oil ratios and the conversion to atomised usable combustion.   

I have still got some elf Kart oxigentator here, i hope to test next time out to see if any differance is had by blends in the fuel. I know ill be lampooned by the forum petrol engineers, but these TM motors dont seem to run what i would call well on unleaded and there must be a reason for that, especially if they ran fine on there current carby set ups for the last 10 years on lead based case.  Somthing has to have change on them all for this to be a common problem.   Where there is smoke................. put out the fire. heheh

anyhow sorry im rambling now.  i have no reason to believe anything other than i have no other explaination at this point for all 3 of my TM 250's running flat on the tune that i got them in, its just another theory, or simply the TM is a shit motor compared to the many small frame honda and yamaha reedies i have tuned over the years.    i have no real idea im a Suzi noob but the tune they are in now is shit and not what i would consider acceptable power, i would be happy for a doc or lozza ro make them run like they should if there is another answer  :'(

[oldfart]

Freaky
           I am the new owner ....picked it up last weekend  , No it won't drive me mental as I have plenty of other projects to pass the time away .
I had the same sort of problem with Docs Mighty TS 400 , problem was solved by using me Pe 400 carb with with 55 pilot and 320  mains using high octane racing fuel   
 
Will try the 25 pilot and 180 mains ...if that don't work I'll take your advise and get the electrics checked out
I recon your spot on about the fuels , might drop a litre or two of AV gas in to see if the works 

Sheezas look at the time ......good night

[Lozza]

Having trouble working out what the problem might be Freaky, but I think there maybe something very basic like float height to low or something like that.Has the inlet port been modified? The symptoms you describe don't sound like engine sound more like fuel to me.
Hows the foot Stew?

[Freakshow]

i tell ya 180 mains will fix it !  its the shit unleaded....................

[cyclegod]

i tell ya 180 mains will fix it !  its the shit unleaded....................

Try some 100 Octane race fuel with a lead replacement additive and an octane booster mixed in. It works a treat and the leftovers really get the whipper-snipper going too 

[DJRacing]

Have you looked at the "Needle Jet 'O-6' ". Is it worn?? In my experience(which could be sh!t all) the needle jet wears oval shaped and half throttle becomes every flat/rich and makes the bike hard to get on the pipe. Also check the needle for any kinks/bends. I understand what you are saying about dropping the pilot (25) and the main(180) and if it runs with those jets great, but is it still short on mid-range, then try a smaller needle jet of 'O-4' or at least a new O-6.

[Freakshow]

I hear you DJR, what im trying to get him to do is make a big impact , big enough so we can say carby(fuel) or not .

he can always fine tune it after we get the biatch going properly.

180 ! 180 ! 180  ! 180 !!!!!!!!

[GD66]

 So, you're virtually saying, try a 180 jet, then....

[oldfart]

Todays up date .....  Installed a 25 piolt along with 180 as suggested along with new fuel ( shell optimax ) ....kick kick kick ring ding ding ringgg
ringggggg ding ding put it into gear let the clutch out ring blurp blurp blurr then loads up.
Change the main jet to 170 ..... stationary it revs its tits off same old thing when under load it dies in the arse very much the same as the old CR 125 did when they flooded
Freaky I'm getting good at changing mains and pilots under 4 minutes flat 
Sprayed aero start around the intake manifold  while motor was running and there was no change in revs which is a good sign
Next I will check out the timming ....might rotate the base plate a little to see what results I get

[Freakshow]

Its not the jets.

You have a differant problem. 

next change the carby incase you got something funky going on in the guts of it, floats ,fuel shut off needle etc

next take the whole ignition off and send it to someone to test it, specially those black boxes, mine died as soon as i did the jet change, i put in a tm 400 to test it and it went like stink out the garage door. the original black box has never worked since F.N.W

LEave the 180 jet in it and push the pilot back to 35.  thats you base. now you can piss about with everything else until somthing make it go rinngga ding ding barrrrrrp baaaarrp 

Failing all that take it to CD5 and march right up to Joel and say fix this big guy 

[suzuki27]

Get out your original and or Clymer type manual and go to the ignition section-I have had several electrical problems over the years that I would have sworn were fuel related.Then get a multi-meter with ohms etc capabilities and start checking readings as per manual.My last one proved to be the last thing I checked-the secondary or plug cap lead coming off the ignition coil was as dead as a maggot-the bike would start easily but under load(higher RPM) and would break up badly,like it was out of fuel or spark etc.I put a 2nd hand coil on I had available and presto- a very long standing problem fixed.Next move was going to be a "leak-down" test to check for any air leaks and if that didn't fix it ,I would gladly have torched it-stick with it and do the simple things first.