New engine worries ( 1st build)

Discussion in 'Motorized Bicycle General Discussion' started by Denisesewa, Jun 11, 2012.

  1. Denisesewa

    Denisesewa New Member

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    I have taken the bike for a couple short rides so far going super easy on it, it runs great at first but seems to be getting hot quickly and after about 3 to 5 minutes it stops idleing, shortly after that it sounds like its " pinging". This is a BGF slant head with a DAX carb with #75 jet, Stock exhaust.
    Fuel mix is Golden spectro at 20 to 1 ( i've used this oil in my trails bikes for years at 70 to1) , the plug looks dark chocolate but not wet or oily and there is black snoz oozing from the pipe so I think its rich rather than lean, I am at 5000 feet elevation. If I let it cool for a few minutes it starts right up and idles.
    So, should I be worried? is this just break-in woes? I cant find any threads on this so any advice and experiences would be appreciated.
    "D"
     
  2. Pilotgeek

    Pilotgeek New Member

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    That does sound a bit rich. My elevation is around 600ft and I run around a 68 jet. When mine runs rich, it sounds kinda funny, not entirely sure why. Does it run okay despite making noise, or does it heat up and then not want to run? I would possibly try putting in a smaller jet, but you may just want to run it as is for another tank or two.
     
  3. Bikeguy Joe

    Bikeguy Joe Godfather of Motorized Bicycles

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    I would go to 24 to 1 as that will make for a RICHER fuel to air mixture (cooler running) and also a LEANER oil to gas mixture (helps with the dripping oil)
     
  4. Denisesewa

    Denisesewa New Member

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    Like I said the engine gets hot, starts sounding bad and quits idleing, I took the head off this morning to check for signs of seizing, everything looks good, if I can only run it for a couple minutes at a time it'll be next year before its broken in.
    Not sure I understand how going with less oil makes for a richer fuel to air mix? I purposly went heavy on the oil for break-in as I know this is a clean burning oil and wont foul the plug, I look at the ooze from the pipe as a good thing for break-in.
    So, Pilotgeek, you are running a 68 main jet in an RT carb at close to sea level?
    Should I keep running this as it is ?
     
  5. Pilotgeek

    Pilotgeek New Member

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    Regarding oil mixture making it rich or lean:
    If you add more oil, that oil displaces the gas, resulting in a mixture that has less gas available to burn and more wasted oil. If you add less oil, it will leave you with more gas and a richer mixture. If you have 16:1, 16 parts of that are fuel. If you have 32:1, 32 parts of that are fuel meaning it's going to act richer. I found it hard to believe when I first heard it, but it does affect how lean or rich your bike runs.

    Yes, I have a 68 jet, and I am running an NT carb. You may want to try getting a smaller jet in the future, however, I'm now wondering if you have an air leak that shows up once your engine gets warm. Does your choke lever make a difference? When I had an idle problem, I either had to turn down the idle so far that it wanted to die, or the engine would want to rev up high and not come back down. The common places to check are where the carb attaches to the intake, and the crank seals. Try spraying those areas with brake cleaner; if it revs up when you spray it, it probably has a leak.
     
  6. biknut

    biknut Active Member

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    Probably running rich. When a motor is cold, it runs leaner, then as it warms up it gets richer. That's what a choke is all about. It allows you to make the motor richer when it's cold.
     
  7. Denisesewa

    Denisesewa New Member

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    Well I found the problem, The petcock is clocked wrong so when the lever is straight down it is just barly dripping, when at 45 degrees it flows a very small trickle, the holes in the seal are tiny, so I replaced the petcock with a drain valve which has full flow, went for a 15 minute ride and it ran fine ( although very rich which is what I want for break-in) Idle remained perfect through out the ride and the engine sounded good the entire time. I did port the intake and made sure it was sealed as well as inspected the crank seals.
    I dont think jetting of an NT carb has any relationship to the RT carb, anyway, I am releived.
    It would be nice if these kits came with at least usable parts, lesson learned, dont assume ANYTHING actualy works . I wonder if the people of China ever buy this stuff or just pawn it off on the stupid * rich* Anglos.
    O-Well, on with the build.
    Thanks for the advice and insight, much appreciated !!
     
  8. Ciro

    Ciro New Member

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    I think there is some confusion in this thread about rich and lean when it comes to oil/gas mix, when discussing air/fuel ratios more fuel does mean a more rich mix but with all my years of riding 2 stroke dirtbikes the more oil in the fuel the more rich the fuel is, for example when racing and having issues with plug fouling during races I went to the local kawasaki dealer for advice and was told to lean it out to 40:1 instead of 32:1 that I was running. I think when dealing with oil/gas mix it is more rich in oil @ 32:1 (rich meaning more) and more lean @ 40:1 (lean meaning less). With air/fuel mixture the fuel is what is addressed when saying rich/lean meaning more/less and when discussing oil/gas mixture the oil is addressed when saying rich or lean.
     
  9. Pilotgeek

    Pilotgeek New Member

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    Ciro, that's true, but a rich oil/fuel can actually affect the air/fuel mixture and make it lean.

    Also, switching to 40:1 instead of 32:1 will help with fouling, but it may not be addressing the issues. A properly burning mixture should burn/clean the plug even at 32:1. I would've suggested possibly switching to a leaner jet and a hotter plug (but that gives a level of risk that a dealer may not want to be responsible for).
     
  10. Ciro

    Ciro New Member

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    The dealer may have had issues telling me what might really help but they ended up sponsering me later on once I started winning races (loved the free parts and stuff!) I honestly don't think I ever found the real problem just worked around it, I eneded up re-jetting the carb for a leaner mix, running a super hot plug and leaning the fuel mix out to 50:1 and it didn't foul as often so I could make it through an entire race but I was still changing the plug inbetween races bc if it didn't foul the first race it would on the second, there were days where I would have to let it warm up with one plug and then wait for it to foul bc it always would once warmed up and I would change plugs even before the race!
     
  11. multipaul

    multipaul New Member

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    An interesting numbers game, I hope:

    Changing the mixture oil/gas from 1:16 to 1:50 changes the air/fuel ratio as if one would mount a 69,5 main jet instead of a 68 one.

    In other words, it makes the air/fuel mixture nearly about 5% richer.

    Multipaul
     

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