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Fuel and fouled plug

Discussion in 'Technical and Troubleshooting Torque' started by Tiga, Jan 24, 2006.

  1. So lets say you fouled one of your spark plugs. I'm guessing the relevant piston will still keep going up and down so long as the other spark plug is still working (and running the crank shaft). So what happens to the petrol/oil mix (I'm talking 2-strokes) that would normally flow in the crank case and end up being compressed and exploding? Does it just get forced out into the exhaust in an unexploded vaporised state or does something stop it?

    Is it different for different bikes?

    Sorry if this seems to be a stupid question
  2. Quite right. The unburnt fuel is simply tossed out. It will foul the muffler after a while and if the cylinder is then cleared and fires, the oil in the muffler will heat up and come out as a thick smear, black. Sometimes it gets hot enough to get smoky, then clouds of it until it clears.

    Pays to fix asap as if enough oily stuff gets i the muffler you might have back pressure problems.

    I had a suzy that did it to me, by the time I got home to get a clean plug you could hardly see behind me for smoke. I had to take the muffler off and wash it in petrol to clear the thing.

    I carry a spare plug. Double bangers should always carry a spare because they can foul more easily than a 4 banger.
  3. Brian you are a legend! That was my next question. I fouled a plug and now my bike is now sooooo loud. I got harassed at the lights yesterday for noise polution :p

    Changed the plugs but not sure how to fix the exhaust. There is heaps of oil along its base, to the point where it was dripping a little before :oops: Does this still sound consistent with fouled plugs?

    Is this difficult? How exactly do you wash something in petrol? Do you stick it in a bucket of it, hose it down or what?
  4. Becoming quite the mechanic.
  5. You stopped at a set of lights...... and somebody complained about the noise...did ya rev the crap outa the Prilla and give em a face full of blue smoke :LOL: :LOL: :LOL: :LOL: :LOL: ...

    Luddites... the best thing about 2 strokes is the bloody noise..
  6. We have a saying at my house...

    "two stroke? two bad!"
  7. Washing stinger type mufflers in petrol can be a definite petrol fire waiting to happen

    That used to work on the older type solid pipes ie Suszy 550 250 etc but since the late 80s most manufacturers swapped to a stinger type muffler that was packed with absorbent material / solid internal type.

    Be careful ring your aprilla dealer and ask if the mufflers can be repacked ??

    If so get some off the packing and strip muffler and repack and then all will be right with the greenie's of the world
  8. :LOL: :LOL:
    It was on Smith St and the two guys were much bigger and ugglier than me. Plus they looked like they hadn't had their hit of whatever it was they needed for a while. I was very glad I had some ear plug in and couldn't hear most of what they were yelling, particularly once they worked out I was female :shock:
  9. Ok, can definitely be repacked cheaply, which from what you've said sounds preferable

    If I don't re-pack immediately is it just a noise/smoke issue. What about the back pressure issues Brian spoke of. Can anyone explain this?
  10. its actualy not something thats easily explained exhaust gasses are pressure waves ... that can affect the whole induction process ... try this analigy

    a full bottle of beer .... if u up end it and let it poor it will let air in to the bottle in huge gulps between letting beer out ............ if you angle the bottle and poor it runs freely and faster ....

    not the best ... but .. that will do
  11. All my text books are at home so this is from memory

    All two stokes that run expansion chambers rely on two principles sound and pressure wave. as the exhasut port opens the sound wave travels throught the expansion chamber and hits the end cone (where it comes down to the small pipe that your stinger attaches) it is then bounced back in the chamber to meet the slower gas pressure wave to slow it down promoting the inlet charge to stay some what in the cylinder.

    this leads us to the issue that iff you run no muffler there is less sound wave to return to meet the pressure wave which means more charge is getting straight out off the exhaust port and running leaner and more unburnt fuel oil charge in the exhaust port

    Hope this helps
  12. The effect repacking will have depends on the construction of the muffler. If it's the straight through race type it will just reduce smoke and noise. If it's a baffled muffler (why would you run a baffled muffler on a 2 stroke?!?!) then you may see better performance from a repack.
    If it's the latter, invest in some new cans and a rejet. It'll be a whole new bike.
    If the bike is fouling plugs, chances are it needs the jetting checked anyway. Probably running too rich for summer. You really should change the jetting twice a year in Melbourne because of the diverse temperatures. At bare minimum adjust the pilot screw.
  13. well done bruce .... exactly
  14. but that aside
    i think aprilia girl should dig a hole .... have the thing blessed and bury it ......... that bike seems to be the motorcycle equivilant of the anti christ
  15. There's always the "Italian tune up".
  16. Yea but its a damm suzuki RGV Donk

    Thats the problem its its just a Japo maskerading as italian
  17. Thanks Brucey, I kind of get it now. That was a good explanation, it never really made any sense to me before :)
  18. It's got aftermarket race type pipes so I guess it's just a smoke noise issue.

    Jetting should be ok. Pete the Pom fixed it all up for me in December. It used to be a track bike so had oversized jets but is back to standard settings now.

    I think the fouled plug was my fault. Here's my theory tell me if it's crazy.

    I forgot to turn my fuel tap on about two weeks ago (hence my question in a previous post about whether I could leave it on all the time). I was in a crappy traffic situation and didn't get to the tap in time so I stalled. Before that the bike was running fine. After that it ran like crap. I think that the petrol flow didn't cease abruptly so there was a period of time where the bike was running really rich before it ultimately stalled, thus fouling a plug. I've got new plugs now so I'm going to check them later this week to see if they are still oil free. If they show an oil build up again then that would suggest my theory is not correct.

    Any thoughts?
  19. Aprilla girl you have had the most appauling run with this bike and dont worry lots of us have been there before, lets not forget that you are riding the closest thing to a 250 gp bike there still is available to us however it should run a lot better than fouling plugs excessive oiling issues etc that you have now.

    Do you have a good workshop manual for this bike??

    I know that you have had it fixed / tuned by aprillia dealers in the past (what a saga) is it time that you went some where else (Mick Hone / Raceway Suzuki ) etc for a tune etc to get a base line on where it should be ???

    Just my thoughts
  20. I know your bike sounds great and smells good, but you really must be developing an infinite reserve of patience by now.

    Bury the thing at the crossroads with a stake through its innards!