after 30-45 minutes I lose torque and speed?

Discussion in 'General Questions' started by dotcom, Oct 20, 2014.

  1. dotcom

    dotcom Member

    My top speed is about 29 and it pulls very well lately but today I went exceptionally far (about 20 miles round trip) when noticed it on my way home. I left the motor off for about 2 hours and then the 10 miles back home I was about 3/4 of the way back home when I noticed I slowly lost about 30% torque and speed. 20mph was no longer easily attained. I haven't ridden since but it was just awhile ago.
    Here's my work of art and my next one that is in progress. Seats were switched for comfort;) I just painted the 2nd one flat camo green on the metal frame.

    example4.jpg example.jpg example2 (1).jpg example2 (2).jpg example3.jpg

    armygreen (1).jpg armygreen (2).jpg
     
    Last edited: Oct 20, 2014

  2. crassius

    crassius Well-Known Member

    even 29mph seems a bit low - I'd be looking for compression leaking somewhere & getting worse
     
  3. dotcom

    dotcom Member

    Well my speedometer is junk and hasn't been working for weeks now. It trips non stop lately and I haven't figured out how to fix it but last time it was working I hit 29. Since, I have added the engine mount tensioner. the rear sprocket adapter and sprocket and the new high performance head so i think its very possible im surpassing 30+ but I haven't checked my actual speed since added them. I just got back from riding it for about 15 minutes and its as good as ever but for some reason, I think if I ride it strong for a good 30 minutes, it will start to under-perform. Im just not concrete with that theory because of my mechanical background
     
    Last edited: Oct 20, 2014
  4. MotorMac

    MotorMac Member

    Just a thought, is it possible that your gas tank is developing a vacuum after 30 minutes of riding and starts to starve for gas? try just putting the gas cap on loose as see if it keeps going strong after 30 minutes. theres a little hole on the gas cap that needs to be kept open , Sometimes dirt gets in and clogs it.
     
  5. dotcom

    dotcom Member

    sure I guess that's a possibility though im thinking it has to do with the quality of engine that it becomes fatigued, if that makes sense:)
     
  6. piecepatrol99

    piecepatrol99 Member

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    I see you're running direct drive...
    A similiar loss of power/speed happened to me with my jackshaft kit. The left sprocket came lose and threw the alignments off on the chains on both sides. A quick fix...

    But its also happened due to inadequate lubrication on the bearings. They get sticky when they get hot.
    Personally I use wheel bearing grease for cars on my axels and bottom bracket...
     
  7. piecepatrol99

    piecepatrol99 Member

    I have two speedometers on my bike. One is completely wireless. That one I noticed was reading 42mph while I was stopped at a red light. My experience with two ways radios lead me to suspect interference.
    I pulled my corded speedometer out of mothballs and ran it simultaneously off the same magnet. Corded gives me steady solid readings.
    I'm not saying chuck your speedo, just be aware of your surroundings. Neon and flourecent lights and L.E.D. lights on car tail lights cause a considerable amount of RF interference.
     
  8. Fabian

    Fabian Well-Known Member

    29mph is high for me. Some days, my bike is struggling to go faster than 4mph
     
  9. Fabian

    Fabian Well-Known Member

    A 20 mile round trip is nothing. The engine barely has enough time to get warm on a 20 mile round trip.
    Talk to me when you do a 120 mile round trip!


    My bike doesn't even do 20mph, even with just about every performance modification thrown at it: http://i56.servimg.com/u/f56/16/57/79/33/multi_15.jpg
     
  10. Fabian

    Fabian Well-Known Member

    :iagree:
     
  11. Purple Haze

    Purple Haze Active Member

    I think that hi-compression head blew out the seals. The stock seals are notorious for failing, even with stock compression.
     
  12. butre

    butre Well-Known Member

    does cylinder compression do anything to crankcase compression?
     
  13. piecepatrol99

    piecepatrol99 Member

    I'm a recent victim of 'snake bite'.
    Last week I pulled the shut off valve from my new tank to apply more teflon tape and seal a leak I've been chasing for a month. I was surprized at how much garbage was in the tank and now attatched to the filter on the valve/in the tank.
    I believe I didn't think to say this before because the filter wasn't obstructed enough to starve the motor.
     
  14. piecepatrol99

    piecepatrol99 Member

    Good question. Might be better answered by some one else but I'll give it a go...

    Cylinder compression should not directly affect the crankcase. The rings on the piston should seal the combustion chamber isolating it from the crankcase.
    Compression in the case should be 'cause' by the the motion of the pistion and controlled by the integrity of the rings, bearings and gaskets on/in the crank case.
     
  15. Fabian

    Fabian Well-Known Member

    I agree with your logic.
     
  16. Fabian

    Fabian Well-Known Member

    :iagree:

    In 5+ years i have only had one (1) crankcase seal blow out.
    My experience has shown them to be surprisingly reliable.
     
  17. piecepatrol99

    piecepatrol99 Member


    The only instance I can think of where cyllinder compression would affect the crank case is changing the crank it self and/or the piston arm or modifying the cyllinder body and piston for more volume/higher compression.
    But that's getting in to modifying the motor...so yeah everything is going to get thrown off...

    Stock motor with no more than upgraded parts should not affect crank case compression.
     
  18. butre

    butre Well-Known Member

    that's what I was thinking, I can't think of any reason for cylinder compression and crankcase compression to correlate in any way, other than possibly changing cylinder compression by increasing the stroke
     
    piecepatrol99 likes this.
  19. piecepatrol99

    piecepatrol99 Member

    2 stroke and 4 stroke are basically constructed the same in that the crank case and combustion chamber are only separated by the piston rings.
    the 4 stroke differs in that the crank is bathed in oil.

    that being said, why would there be compression in a 2 stroke crank case? isn't the crank case supposed to be a vacuum?
     
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