2-stroke 'over heating' myth...

Discussion in 'Motorized Bicycle General Discussion' started by Venice Motor Bikes, Mar 25, 2013.

  1. Toadmund

    Toadmund New Member

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    Better than having it drain from a hairline crack in the tank all winter.
    That explained the oily residue on the floor.
    And my missing gas.

    Oh, and back on topic, if your motor is at full operating temp in 5 minutes, why would it get hotter in 10, 15 or 20 minutes more? The gas still burns at the same temperature, the motor still cools at the same rate (moving rate, still rate)

    It only gets so hot.

    Same thing as a blow torch flame, it only gets so hot, the flame don't get hotter with time.



    Ehhh, people are dumb.
     
  2. bairdco

    bairdco a guy who makes cool bikes

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    yup, me and tom usually agree, and i understand your theory, but my experience totally contradicts it.

    my first hopped up motor would bog after a few minutes at WOT. letting off the throttle for a few seconds, then back on it again, and the bike would take off again, only to do the same thing.

    it just seemed like it was running out of fuel.

    this was on a reversed jug gt4 starfire with a top speed just under 50mph.

    i checked for proper fuel flow, cleaned the carb and the air filter (a dirty, oil clogged filter will make your bike bog, too.) changed plugs, changed float settings, made sure my wiring was good, and everything else possible, but the problem continued.

    going back to my original hunch, i changed the petcock for one that flowed a lot better, and the problem went away. everything else was the same so that ruled out any other gremlins.

    several other forum members backed me up on this, so i feel the stock petcock can't keep the NT carb at full capacity on a modified engine at WOT.

    the float bowl holds a very small amount of fuel, so it's plausible that even a miniscule amount not getting the carb quick enough could cause it to bog.

    i've repeated the same results on other bikes, so i believe it's been proven.

    when i'm back up and riding, i'll put the stock petcock back in and prove (or disprove) it once and for all.
     
  3. 2door

    2door Moderator
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    I'll be here.
    But I ask that you do the test. Time how long it takes to drain the tank with the old petcock and compare it with how long you can ride on a full tank of fuel. Even at WOT. Just for grins, compare the two petcocks for drain time. That would be interesting too.

    I have far too much respect for Baird so I certainly am not disputing his experience but I suspect there are other factors involved here. Possibly a petcock that does not flow a full stream, fuel foaming due to vibration, an extremely low float level, any of those can contribute to a fuel starvation condition. But not an engine that eats fuel more quickly than fuel can free flow from a tank; if in fact it is free flowing.

    Just don't rush your recovery, Baird. We want you all better :)

    Tom
     
  4. Goat Herder

    Goat Herder Gutter Rider

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    I can hurt a 4 stroke the same way with a shift kit. I have a Mountain here that would prove it. When in a bad gear with a parasitic drag draw of a J Shaft a engine of the same cc size category as your H.T. will have problems.

    In fact .
     
  5. Goat Herder

    Goat Herder Gutter Rider

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    My Morini fell on its face with the stock Goped in tank filter and my aftermarket petcock. Full throttle cut out after maintained speed I could predict it like clock work up to a block or so at wide open throttle. Any other time just cruising around it ran flawless even at wide open throttle just up to about a half city block then it would die just like letting completely off the throttle and about a second later picked back up only to do it again...

    So reworked all of it with out the in tank filter first . Took longer to do it after the petcock replacement and a sweat larger inline filter ''instead of the dime sized stock one'' Bingo flawless in every way.

    My first kit bike ''Chinese H.T.'' had a issue with the stock peanut in tank filter clogged up. When I attempted to clean it up the screen fell apart. Same story.

    In these cases a free flow test just as 2door mentioned showed it to be evident as well.
     
  6. Goat Herder

    Goat Herder Gutter Rider

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    I would also like to add that even at a high altitude here my H.T. motors that I have tried never ever did overheat. Even when ran for whole days at a time.

    About two summers ago my Morini did when I absolutely tried to break it on purpose. Was testing everything I knew and was in a very destructive state of mind...I had a parasitic dragging J Shaft set up on it at the time and climbed a ridiculous incline against the Sandia Mountains here in the month of July on a very hot day for about 16 miles straight. Non Stop!! No Breaks... With a near worthless Nuvinci hub running at constant 11,000 rpms. COMPRESSION RATIO 12,5 +/- 0,5 : 1 http://www.morinifrancousa.com/engine3.htm

    https://www.google.com/search?q=nuv...s=org.mozilla:en-US:official&client=firefox-a

    Any 4 stroke in this class would have had the exact same problems guaranteed

    Well Nuvinci did not impress me much as the hub it self got so hot it peeled the flesh from my hand when I touched it. Had to immediately spit on my hand to get composure.

    The Morini 2 stroke is a very durable engine and I could not break it. Always Ran good oil and is still brand new with cross hatch still present in the cylinder jug through and through at 10,000 miles now.. Checked and verified just about a week ago.

    I no longer run it it with a J shaft and run the engine just as the manufacturer intended it to be. Never ran into any kind of issue again. I run it on many occasions for whole days at a time too. COMPRESSION RATIO 14,5 +/- 0,5 : 1 estimated a little higher now for a 21mm carby etc. At even higher rpm's !!

    2 Stroke engines are awesome engines. They will run just as long and hard as the best of them. If not even better! There are many good brand 2 stroke engines besides the ones I mention out there to be had that are good engines.

    I would use them all

    Absolutely!!
     
    #26 Goat Herder, Mar 26, 2013
    Last edited: Mar 26, 2013
  7. Bob K

    Bob K New Member

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    They are called "heat engines" for a reason.
    I'm really old and I have never siezed a 2 stroke
    that was jetted correctly. Why? Because the hotter they get,
    they start going "rich" because the proper mixture at "normal
    temperatures" starts vaporizing more completely. So you might
    build up more carbon in the combustion chamber, but, siezure?
    I have not seen it ( with proper jetting)
    Power loss?
    Always.
    It's a heat engine.
    Show it some mercy and you won't have to buy parts.
    But, correct jetting is YOUR responsibility.
    Step up.
     
  8. maniac57

    maniac57 Old, Fat, and still faster than you

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    Perfectly states my opinion.
    "2 Stroke engines are awesome engines. They will run just as long and hard as the best of them. If not even better! There are many good brand 2 stroke engines besides the ones I mention out there to be had that are good engines."

    "I would use them all"

    "Absolutely!! "


    Goatherder gets it!
     
  9. Goat Herder

    Goat Herder Gutter Rider

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    I concur with Bob.. he has a really good point too on air fuel mixture! Very important to properly identify. Of course the old fashioned spark plug chop makes for good identification as with any motor.

    I wanted to add if a fellow messes with the timing look out. Bad idea!! I played with the timing on the Morini in the coldest dead of winter for a brief spell... only to put it right back where it was. . This would sorely torch-er any motor in the summer and burn one up just as well as a lean condition.
     
  10. 16v4nrbrgr

    16v4nrbrgr New Member

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    There's also a way you gotta ride them, blip the throttle a lot to keep it oiled on downhills, light load cruises, things where the motor would otherwise be spinning with only idle fuel flow going though at higher crank speeds. Maybe that's where the heat problem is arising, people are going along with steady throttle never giving the engine its oil, with cylinder and head temps fluctuating like 50 degrees between going at speed and idle, this can cause all sorts of weird issues. I have to conciously think to blip the throttle on long braking zones even though there's no downshifts, to prevent bad stuff. If you've ever seen the clip of James May wide eyed on the brakes hard and blipping the gas on an old Saab going down a steep hill, nearly crapping himself, you'll know what I'm talking about. Fortunately for us there's manual clutches and centrifugal clutches so its not an issue, its just a habit to form.

    That must mean my lapped head is around 16+:1 because I had to take off a lot to get the lathe faced head to true out flat. Wow, that's crazy, 91 octane always it is!

    I was thinking maybe carbon deposits or irregularities in the heads in HT's could cause hot spots in the cylinder if running lean already that could really turn into a predetonation meltdown situation, maybe that's what the deal is, and why some have had problems, others not, there's like 10 heads out there for HT's.
     
    #30 16v4nrbrgr, Mar 27, 2013
    Last edited: Mar 27, 2013
  11. bairdco

    bairdco a guy who makes cool bikes

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    the main point norm is making is that there's no need to stop and rest your motor after 20 minutes during break-in, or whatever the manual says, so it can cool down.

    this question comes up a lot from new members worried about destroying their new engine on the way to the store or something.

    the generic term "overheating" doesn't cover piston meltdowns due to lean conditions, air leaks, blown headgaskets, etc.

    all these things can and will happen to the HT motors, but they're caused by other problems, not just long running times.

    every motor i've destroyed had a root problem, such as too high compression, weak pistons, rings, bearings, ring clips and pins, etc.

    an air leak, poorly tuned expansion chamber, warped head, lean fuel, etc, can overheat an engine and burn up a piston or fry a bearing, but a tuned engine can run all day as long as no other harmful conditions are in play.
     
  12. Goat Herder

    Goat Herder Gutter Rider

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    My Morini exept for the 5.8 s6t and smaller models needed to be blipped on the throttle in my experience because the carb loads the engine up. I have gone for extended periods of time in many positions. If I idle for very long with my bigger carbs they try to load up. That personality changes with the season too and sometimes I re-tune for it as well. Despite getting a clutch that would crawl gingerly around and rip!

    Small price to pay for a tiny bit more power. Its like a little dragster engine:)

    I concur with Bairdco as he said it right. This was pretty much the point.
     
    #32 Goat Herder, Mar 27, 2013
    Last edited: Mar 27, 2013
  13. 16v4nrbrgr

    16v4nrbrgr New Member

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    Yeah mine loads up too, I set the idle screw high sometimes to make it easier, then dial it down once its warmed up. It still needs the typical two stroke brapp every once in a while to clear it out. I'm glad the stock jetting is rich, I'm gonna keep it that way, its safe and the air can be really cold and wet here, need lots of gas to compensate.
     

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