Exhaust I drove it without an exaust pipe for about 4 miles...

Discussion in '2-Stroke Engines' started by fogg4444, May 11, 2007.

  1. fogg4444

    fogg4444 Guest

    My exaust pipe fell off and I drove it for about 4 miles on pavement and a dirt trail... 9It was so loud...crazy loud, like a harley!!) It dosent seem to be working right, now. I have to idle at a much higher speed now or else it will bog down and my fuel seems to dissappear faster. I dont know what is going on. help?

    BRIAN :sad:

  2. Patch

    Patch Guest

    the exhaust pipe provides necessary back pressure to the enigne...so if you ran it without the pipe, the unburned fumes (that give you power and gas milage) will just escape. I The fumes also provide a sort of seal-if you will- that keeps the engine running rather than boggin out.

    I would say lean runing conditions...out her back on just to be safe :???:

    So I hope that bit helped you?!?! :???:
  3. fogg4444

    fogg4444 Guest

    long term?

    yeah that helped, but will it cause any long term damage?
  4. Haggard

    Haggard Guest

    Hi I may be mistaken but I believe the exhaust pipe helps to disipate the heat from the head. pretty sure the engine would run hotter without a pipe which may cause undue wear.
    also ,with an open exhaust port , your allowing for contaminates to enter the engine,
    If you were riding off road or in a real dusty area, Yes this could certainly have adverse effects on your engine

    Hope alls ok

  5. Guest

    Guest Guest

    You rode it with the exhaust off.

    Put it back on.

    The exhaust needs to be on there for a couple of reasons, which I won't go into now.

    No exhaust = no low end power and will cause lean running conditions.....really bad.

    Put it back on.
  6. fogg4444

    fogg4444 Guest

    still isn't running well

    it still doesent run well. i put the exaust back on with a piece of leather for a temporary gasket, it seems to seal fine for now. The bike still feels weird though. I cant go nearly as fast as before. I used to be able to go around 35 mph but now it gets maybe a top speed of around 15 and I have to fiddle constantly with the choke while I ride or it just slows down immediately. if I pull in the clutch and rev it it jus bogs down and stops unless I rev it real high to keep it going... what do I do now??
  7. Guest

    Guest Guest

    You have an air leak...check your intake gasket and after you put it back together, make sure the carb is all the way on and tight.
  8. saylor

    saylor Guest

    no, if you rode it too much with no pipe, you hurt it.

    An engine needs the back pressure of the pipe.

    I think it can draw in cool air thru the exit port when it's not supposed to and damage stuff, I think. I wanna say it scorches or burns something, the piston maybe? hold on I'll remember sooner or later.
    damn maybe it cracks the head. That's what just popped into my mind.

    but I think you hurt it.
  9. Guest

    Guest Guest

    I ran a mac 101 kart engine for a whole summer with no exhaust, just the open port- no damage.

    Engines don't "need" backpressure, but work better with it, especially on the low end.

    The exhaust pipe actually retains heat, not disipate it.

    There is the possibility that you got a crud chunk/rock/sand inside the cylinder, but if that's the case you would have felt it right away.

    Check for air leaks. From what you describe, you are running very lean....not good.
  10. gone_fishin

    gone_fishin Guest

    carb connection or intake gasket is my best guess, too.
  11. azbill

    azbill Active Member

    I rode my deviate for approx 200 miles with just a 1" stub till I got an exhaust :shock: :shock:

    I agree, it sounds like carb to manifold or manifold to engine leak 8)
  12. saylor

    saylor Guest


    I guess we disagree :)

    I maintain that it is taking in air via the exhaust port, when it should be drawing gas/air from the intake manifold only, thereby allowing excess air to come in to the gas/air mix in the cylinder, and "leaning" it out.

    so what happens if you run an engine lean too long? Does it get hurt?


    a lean engine runs hot.

    then what happens?

    you warp or crack the head.

    and read that in the past tense, , ,it TOOK in air... not "is taking",, as he has put the pipe back on since... I forgot myself there a bit.
  13. Dockspa1

    Dockspa1 Guest

    Think about it for a minute. The cold air being directly in contact with the piston after a hot engine, is definately not good. Expansion and contraction on the piston, head or even the inside jug walls is bound to resize itself with or with out cracks and warps.
    It's just like having an overheated car engine and you turn it off and then add cold water, KAPOOTZS! KABAM! It's history.
  14. Guest

    Guest Guest

    Guys- remember that when the air/fuel mixture comes in throught the INTAKE, it is fairly cold.

    This doesn't hurt or sieze the engine.

    The exhaust on a two stroke doesn't suck air as when the piston is traveling downward, it pushed the (cold) intake mixture out of the crank case and into the cylinder. If anything some of the fresh mix gets pushed out through the exhaust, unburnt. That's partly why two strokes have "dirty" exhaust.

    Also saylor, a couple of things- these engines don't employ reed valves, or even rotary valves, they are piston port timed engines.

    If you read that web page, the incoming (cold) air pushes the exhaust out of the port via positive crankcase pressure. It doesn't suck in the mixture.
  15. saylor

    saylor Guest

    Well, hopefully the original poster will fix his motor and then tell us what the problem was.
  16. saylor

    saylor Guest

    BikeGuy Joe -

    in your previous post - you mention
    Then - in another post, you say

    Maybe you could go into those details of why the exhaust needs to be on there? Obviously there is confusion in the forums, so we need an expert to set us straight.
  17. gone_fishin

    gone_fishin Guest

    just checking in...we're pretty careful 'round here about friction...this is a tech/mech topic, aren't we supposed to be trying to help someone?

    take the differing opinions & personal jabs PM or start a new "debate" topic.

    the OP is fogg4444, and he's moved on to the next step.

    fogg4444: your last post leads me to again advise you check head/jug/intake gaskets & carb-to-intake.
  18. saylor

    saylor Guest

    I'm not trying to create any friction - he said he had explanations that were too detailed to go into, but it's obvious that we in the forums need the detail as we're all just guessing as to what the problem is... so I was hoping he would share... it may make one of us think of something else that could be the problem.

    Anyways augi - point made - this is a tech forum, and let's keep it that way. I appreciate that comment.

    And Joe - no hard feelings. I'm just trying to help the guy, just like you are. We both could be right, or we both may be wrong and his spark plug is hanging halfway out and THATs the real problem... I guess we just don't know until he updates his post :)
  19. Guest

    Guest Guest

    No, it's cool.... You kind of answered the questions yourself there.

    Engines don't need back pressure, but they run better with some, especially at lower rpm's. The kart I ran was run at WOT most of the time, and so the open port gave max output at a very limited rpm range. The engine was jetted properly to be run at WOT with no pipe, so it wasn't running lean. However, if you loose your exhaust on an engine jetted to run properly with it, it will go lean and that's a bad thing.

    Also, the exhaust needs to be there for a couple of reasons- one more obvious one is noise suppression. The other is tunablility over a wider rpm range.

    Class dismissed! :lol:
  20. rcjunkie

    rcjunkie Guest

    Back pressure improves low end torque but at the expense of all out power at higher rpms.

    Anybody who has a motorcycle with an aftermarket knows the hassle of having to rejet their carbs due to the free flowing exhaust over stock.