Question about 2 stroke throttle to rpm relation



  • Hello every one , new guy here, seems like you've got an awesome forum here!
    I have a 1992 Tdr 125r belgarda, it works, but every thing about it is strange, but the most serious thing is the throttle response.
    My question is how should throttle position relate to engine speed, because mine does a thing like this when i give very little throttle like 1/7 the rpms start to rise to 7000 or there abouts , and the bike feels very slugish and consumes allot of fuel about 1 liter to 16km.
    Hope some one responds !
    Thanks



  • So ran to the garage started the engine and the engine started whining , you can see in the video the weird throttle response. Well no riding for me 😞
    link text



  • Yeah that certainly doesnt sound healthy. First point of call would be check for air leaks by spraying WD40 around inlet and various possible areas of air leaks and see if the idle changes.

    Then i would clean the carb and check the jetting, needle position etc.

    Do you get any dark smoke from the exhaust?



  • There is a leak somewhere because a few weeks ago i heard a leak sound coming from the engine , didn't make a big deal about it so forgot about it 😕
    This bike doesn't have the oil pump and the holes in this cover were closed but i noticed that the seal was leaking i opened it and found alot of dirt ( the oil pump assy was not there) can it suck sand thru the gear opening?
    engine side

    I can't find stock jetting online , if you could post them here i would be very thankful!
    And because there're no manuals for this bike (as far as i know) i don't really know which one to order ....
    No, the exhaust is not too thick and is white colored.
    But the scary thing is that it is derestricted , i think the exhaust is from a newer tdr and was cut in half, and alot of other stuff done to it so i have no clue what is factory and what is a botch exhaust
    Got the bike stripped so if you need photos from deeper in the engine i can get them
    frame
    Thanks for the help!



  • Well if if you've stripped it then sounds like you're on your way to getting things sorted. Just be methodical and check specifications for stuff as you go. If its the 32mm dellorto carb as it should be for a belgarda engine then finding jetting info may be a push. You might have to learn to Jet yourself and do it the old fashioned way. Theres quite a few guides online into the theory behind jetting. Callum knows a few good books.

    I would say do all you can to get i back to stock though. They ran pretty damn well. Get an oil pump ( make sure its good or get it rebuilt). Or if you dont want to then get a proper blaking plate and ensure theres no way it could be sucking air in through there.

    If you have the ability to then defo get a load of photos of various bits up and someone may notice something iffy.



  • Finally figured out how to post photos :3
    All photos

    How does one get a seized/rusted swingarm bolt out?
    bolt

    Dont really know how to seal this , i think the shaft needs to be taken out?
    pump

    How does this look?

    And this is my carb, with a broken choke lever...
    alt text



  • @ramekenas firstly that oil pump doesn't leak into the engine or gearbox. Either put a pump on it or leave it alone.

    That carb is inferior to the standard carb get the original one back they are not expensive.

    Swingarm put the nut back on so that it is screwed on but slack. Then hit the nut with a copper mallet as to not damage the thread or nut and that shall release. Some wd berween the engine mounts may help.f



  • @Calum Thank you !
    Good to hear that the pump gap could not have wrecked the engine!!
    Which carb exactly should i be looking for? DellOrto VHSA 32ES , DellOrto VHSA 32GS?
    They are interchangable so all the rubber parts will fit them both , is that correct?
    I was hitting the bolt with a wooden spacer and hammer for quite a while didn't budge, have to try that with a copper sheet spacer.
    And since when do hammers cost 50euros ^^ didn't know copper hammers cost that much, wow!
    Thanks for the help!



  • good photos. love the bit of wood to block the oil pump cable.

    the carb you need is a vhsa 32mm. i do have one for sale. if ypure interested i can get photos.

    agree with cal on the copper mallet. wd40 is good but a specific penetrating oil would probaby be better. screwfix were doing big cans of no nonsense for £3 recently. if you still cant get it shifted then a heat gun on the end might help break it free. just be careful of seals etc unless you plan to replace them anyway.

    swing arm rebuilds are costly though so only do if needed and remember to grease it all well and keep ut greased using the nipples.



  • also on the oil pump front. there are mixed views on their reliability but if rebuilt and the bike is looked after it makes it far more efficuent. i know a guy on the 350 ypvs forum who rebuilds them. im probably getting mine done on the dt engine im doing atm.


  • Global Moderator

    I wonder on the opposite side of things if it's possible for the pump to fail and cause over oiling? A friend of mine says his DT keeps overheating and I reckon it could be too much oil if his coolant is fine.



  • @MIGHTYMAN Whilst it is true fuel cools the piston down, and throwing that ratio out will affect its heat.

    Over oiling will reduce friction in the engine, reducing temps.

    So not convinced on that idea.


  • Global Moderator

    Too much oil though definetly makes heat.. I can't remember the exact explanation but it's something to do with the oil changing the octane levels? My 250 EXC seized when i stupidly put twice the oil ratio into a mix of petrol.



  • @MIGHTYMAN Like I said, that's due to the dilution of petrol, not necessarily the addition of oil.

    For example, KTM EXC 250 Two Stroke.

    Pre mix oil and fuel, dilutes the petrol mixture.

    DT125R, with oil pump, adjust the oil pump to max settings and the fueling stays the same.

    That's in response to your friends over heating problem.

    Other possibilities are contaminents in the Coolant system reducing the specific heat capacity of the coolant, increases temps.



  • Well not much progress today, swingarm is still stuck in the bike ,but i managed to free it from the bolt itself now the swingarm can move without the bolt turning with it , it is stuck on the washers near the head of the bolt
    alt text
    according to this pictue, on one of those parts 7,9,5
    Fixed a few wires and cleaned connectors on the wiring loom.
    What do you guys do when the loom becomes stiff - every wire on mine has insuliaton like hard plastic?



  • @AndyYam
    How much would you want for the carb?



  • 7 is not a washer it's a dust seal.



  • @ramekenas £60 delivered.

    So what is the problem with the swing arm? I'm confused as to how its stuck? the pivot bolt is out now?

    Diesel, coca cola or penetrating oil and then a heat gun is still my best advice.



  • @AndyYam
    Well i tried to take the bolt out for 4 days and nothing happened ,only on day 3 did hear the bearings crunching in there , it is rusted solid and a multiple ton press is required or something like that, i even took a rotary hammer and tried to hammer it out to no avail. The oil fittings in the swingarm look like they never been used you can't see shiny metal there at all, so out of pure despair put the bloody thing back together and filtered the oil and it stopped whining , i have a feeling its clutch plates + dirty oil.
    I changed the oil at the beginning of this season but it was grey-ish all ready looks like the gearbox won't last to long. I thought about it and decided if i can make it running for the rest of this season i will so i could clean up the garage get some tools some books/manuals, and do everything properly during the winter because i need the bike to repair the bike catch 22.