2 Smoke questions?

Discussion in 'Thumpers' started by MCrider, Sep 12, 2010.

  1. MCrider

    MCrider Been here awhile

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    Thinking of getting a two stroke but have heard comments about how they cannot be riden around at less than full throttle for very long without burning them up. Is there any way around this? Can they be set up for slower riding or longer stints at road speed without grenading? Do you check the plug for propper jetting the same as on a 4 stroke?


    Thanks
    #1
  2. little_twin

    little_twin Been here awhile

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    My 07 yz250 has great bottom end and mid range. No need to be pinned everywhere on that bike or any 250 really. Now if your riding a 80 its a different story. Keep an eye on the plug and you'll be fine. Add a flywheel weight if your really concerned about it, but I don't find one necessary.
    #2
  3. JTucker

    JTucker Long timer

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    I rarely ride mine flat out, usually I'm in the woods off the pipe. Proper jetting and timing keep them happy. Luckily I bought mine already set up because I don't know much about them. :lol3
    BTW, I love my rekluse clutch.
    #3
  4. BelnapAir

    BelnapAir On my way...

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    The problem with lugging a two stroke is simply less lubrication. Thats why they all will tell you to "ride the pipe" if your riding in extreme conditions. If your just cruising around, and your jetting isn't so rich as to foul plugs too easily, you can easily get away with putt putting. Just keep an eye out for engine temps. If you notice things heating up, just shift down to the next gear and get the RPM's up. And get on the throttle every now and again to clear out the spark plug for extra security. I've had my CR250 for 6 years now riding mostly sand dunes, and have not had a plug foul.
    #4
  5. anotherguy

    anotherguy Long timer

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    I have a Yamaha YZ465. It runs great from idle to redline. It's not possible to ride it around pinned all the time. Unless maybe you live in Bonneville. It's 31 years old and on the 2nd oversize piston. 2 month old ethanol pump gas and it starts in 2-3 kicks from cold. I'd say you've been misinformed.
    #5
  6. Rogdog

    Rogdog Adventurer

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    Yeah, I agree with the others. I have a 20 year old Yamaha DT 175 with about 35,000 km's on it. It seldom gets pinned, spends a ton of time idiling in traffic with the 7,000,000 or so other motobikes here in Saigon, in the 35 C heat, and with crappy dirty gas. I do run it rich because of the conditions, but it is by far the most reliable bike I have. Starts with one kick, idles with no problem, and will take you up to 100 kph on the rare times here where you get the chance. The only downside I get from running at low RPM is that it will smoke like a bugger.... but drop a gear and run it over 5000 RPM for about 10 secs and your problem is gone.

    It has had one engine overhaul (piston and rings), but after 20 years of spotty maintenance in the worst conditions imaginable, I don't begrudge the $150 USD that cost me.
    #6
  7. boingk

    boingk Been here awhile

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    I owned an Aprilia RS125, and while its not a dirtbike the principle is the same. Its little engine was pushing out 240hp per litre of displacement, and it never had a problem with lubrication because the stock mixer system did a very good job. It stood up to 600 miles a month (mostly 'spirited' :D)before I rebuilt the engine and sold it. You need to ensure that any lube system on the bike is bled and adjusted properly.

    In a nutshell, bleed new oil through to the pump, then hold it in 'open' position while engine is idling. When no air bubbles are visible in the line and the exhaust starts to smoke heavily, release the pump from the 'open' position and give the bike a few quick throttle blips. You should see the smoke increase with hard throttle blipping, but be negligible at constant throttle under load.

    The alternative is to remove the stock lube system (assuming there is one) and run premixed oil/fuel at the recommended ratio, or 1 in 25 if there is no recommended. I've done all this on a 100cc Kawasaki with no problems.

    The main thing is to not let the engine compression brake; always pull in the clutch and use your wheel brakes. The reason for this is that with the engine revving you cannot close the throttle for any extended period (eg long downhill section) as this will starve the engine of petrol, and thus oil... especially if you run premix. It may not be a problem with more modern lube injection systems, but its not a bad habbit to form.

    Bottom line? Perform proper maintenance on your bike and it should be fine.

    Cheers - boingk
    #7
  8. LILBIT

    LILBIT Ride you must.

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    Checking plug color for jetting is a poor method for any engine these days on pump gas. Properly jetted a 2 stroke wil run fine on the road and idle as happily as any 4 stroke. However when air temps change 15 degrees the 2 will need some needle tweaks where most 4 strokes will get by. Idle mixture will vary in 5 degrees but is an easy fix with a screw driver.

    High performance 2 strokes can be a handfull or impossible to jet for road use on pump gas. Lowering compression does wonders but some like a little head modding.
    #8
  9. MCrider

    MCrider Been here awhile

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    Can anyone comment on how to set up on a 2 stroke like the one mentioned above. Should you automatically rejet a MX bike for slower trail riding? If so are there guides to go by or do you just jet up until you foul a plug then go down a few sizes?
    #9
  10. potatoho

    potatoho Cheese and Rice!

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    It will be interesting when the fuel-injection two stroke models start coming out from the major makers. It should solve some problems.

    I have often used my O2 lambda set up to tune the two strokes. A sensor at the header within 5" or so of the cylinder, just beyond the wet oil line. It's not very useful when the jetting is sloppy, but once you get a good wet oil line the O2 sensor stays clean and is great for fine tuning.

    The problem with two strokes is that they don't tolerate poor jetting as well as a four stroke. However my personal opinion is that on the flip side the two stroke will reward good jetting and make some crazy power even on small displacement.

    Keep in mind also that there are other parts to the motor which may grenade. It's very important to research the reliability of the bike brand/model and see if it is suitable. For example, my KTM 105 model is apparently notorious for burning up main bearings, something about a bad crank angle. It's about a 50 hour motor between lower end rebuilds. My KTM 300 is about 500 hours between lower end rebuilds.
    #10
  11. MCrider

    MCrider Been here awhile

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    Most 2 strokes dont come with temperature or O2 sensors, so what do you smokers go by when tuning your bikes? Especially if reading plugs in a 2 stroke is not a good indication.:ear
    #11
  12. Pigford

    Pigford British

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    You CAN still get a fair indication of mixture by plug-reading. The plugs just don't look so brown/tan colour now-a-days with the low lead, ethonol base fuels.

    White and/or green tinged plugs is too lean - BAD

    Tan/bropwn or slate colour is near the target - OK

    Black - too rich or too much oil - BAD

    No matter how old the bike is, use a good quality 2-stroke oil.

    As for shutting the throttle for long downhill stretches with a pre-mix bike - don't worry too much, just regularly blip the throttle (every 5/10 seconds).

    The slow running is more prevalent to the old 2-strokes running old style poor quality 2-stroke oil. With pre-mix, the oil:fuel ratio was higher (more oil) which built up and made the bike smoke and (ironically) 4-stroke as the oil was cleared out of the engine, when it was given the beans after some extended slow running.

    Its usually people who have had little to do with 2-strokes that panic and get sucked into the old horror stories :huh which are mainly B S :lol3
    #12
  13. potatoho

    potatoho Cheese and Rice!

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    Wet oil line method. It gives you feedback on the oil migration.
    #13
  14. Flatulator

    Flatulator Banned

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    aside from the "burning up"

    I think you are not specifically telling people what you ARE going to do with "it" ... and exactly what "it" we are talking about (what bike?)

    Like ... most of the people replying sound like they are thinking you are going to ride a dirtbike mostly like a typ dirtbike gets ridden .... but I suspect you are planning on riding a dirtbike ... for "long" mileage on the street ?

    Heres one thing ... 2 stroke dirtbikes do not act very "happy" on the street ... their cylinder porting is made to "go" .. not 'maintain' .... they will surge back and forth somewhat even though you are trying to maintain a steady speed.

    if the bike isn't happy ... you may not be either.
    #14
  15. MCrider

    MCrider Been here awhile

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    YZ125 or possibly a 250 around the 05 or 06 model. Ridden not so much on the street but back dirt roads, double and single track, no closed MX course. I know there are probably better bikes out there for this purpose but like the power to weight ratio of the smokers. I have never owned one before but do have experience with 4's.

    Does "oil line" refer to the line of oil coming out of the exhaust?

    Thanks for the good info so far, keep it coming Im still hungry.
    #15
  16. potatoho

    potatoho Cheese and Rice!

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    Yes, it's a line where the wet exhaust and dry exhaust sorta meet. The motor needs a wet line to exist at all times, ideally something like 2-1/2" - 3" from the piston skirt. That's usually just inside the pipe's flange area. It is usually clearly seen if you pull the pipe.

    [​IMG]

    Described methods:
    http://shokwerx.com/2strokejetting.html
    http://ktmtalk.com/index.php?showtopic=41083

    I have O2 lambda bung mounts on my pipes, which incidentally are kinda useful for wet oil line check too. You can unscrew the stopper and look into the pipe with a flashlight etc.
    #16
  17. EastBoundAndDown

    EastBoundAndDown Ron - 300XC-W DR650 T1050SE

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    2-strokes are the best bikes on single track. You can jet them close enough that if the temps drop by 10-15 degress, its not lean, and if it gets 10-15 degrees warmer, not to be too rich as to foul a plug or not run well. I'm sure it can handle short spurts of tarmac to get the the riding spots, if thats what your getting at.
    #17
  18. welder

    welder Long timer

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    There are alot of myths about two strokes . Like they sieze pistons alot, you need to keep them "on the pipe", you need to get rid of the oil injection system because they fail frequently. The list goes on and on. The bottom line is that modern two strokes are as reliable as modern four strokes. its the poor quality oil and poor fuel/oil mixing and poor maintenance that kills them. If you maintain them they will last a long time. And no you don't need them to be wfo for them to be relible.
    #18
  19. LILBIT

    LILBIT Ride you must.

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    If a 2 stroke surges at steady throttle it is lean. Same as a 4 stroke. Has nothing to do with the engine type.

    I'd really recommend a wide tranny model over the YZs. Husqvarna WR, KTM EXC or even a Yamaha WR though it's old. Gasgas has a 6 speed as does a KDX. All of the above were street legal in other countries (Yamaha?). I prefer larger displacement bikes as they pull taller gearing much better than smaller. A KDX is a very good choice though due to its mild engine and wide tranny. Very easy to jet. The 220 was street legal in Japan for years.

    You have to pull the pipe and look in it to use the wet oil line method. It can be done by feel but takes some practice.

    For road use i insist on a very light sputter at all RPM. If the bike is allowed to be "crisp" at steady throttle pistons get hot fast. The problem most people have is that most stock bikes can never do this without going overly rich in some RPM area. Many different needles exhist out there and chances are you'll be forced to learn about them. Even a 500- rpm lean spot is a no no. Otherwise run super rich sputter or sieze running in that tiny lean spot. Once you get a baseline weather adjustments are easy.
    #19
  20. little_twin

    little_twin Been here awhile

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    Get the 05+ yz250! You wont regret it. Mine has been the most reliable bike I've owned. Got it new in 07 and its only on it's second top with countless hours. Plus its light enough that you'll be able to pick it up all day long.
    #20