3 questions

Discussion in 'Motorized Bicycle General Discussion' started by fischer550, May 27, 2014.

  1. fischer550

    fischer550 Member

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    1) Is it true that a leaner fuel/oil mixture also richens the motor so requires a smaller carb jet?

    2) 44 or 36 tooth sprocket for break in, I have both.

    3) I live in the Denver area, should I switch the stock NT carb jet from a 70 to a 65 for break-in? Will a motor running way too rich at break in end up with less performance in the long run?
     
  2. mapbike

    mapbike Active Member

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    #1. Leaner/less oil means more fuel in the mix which = a richer mix relating to the amount of fuel in the mix, a smaller jet will lean the fuel mix or a larger jet will richen the mix, all of the china girls I have had come with a jet that is way big and needs to be reduced for the engine to run right in my climate and altitude in Texas which is 1242 ft above sea level if I remember right.

    #2. sprocket size only affects power for pulling the bike along and top speed at a set rpm, smaller 36T sprocket at 4000 rpm for example you will be traveling at several mph faster than at that same rpm when using the 44T, so engine revs lower rpms at say 25mph when running a 36T sprocket verses if you are running the 44T which is fine but will limit top cruising speed a little normally and causes the engine to increase its rpms at the same 25 mph.

    #3. If your engine 4 strokes all the time (makes a constant blubbering sound) and never smooths out and makes a steady purrring sound you are likely running to rich on fuel, yes a jet change will remedy this problem, you can put the #65 jet in the carb, pull the sprak plug and clean it well with some brake parts cleaner and a wire brush, then dry it off and reinstall it in the head, start the bike and go for a couple mile ride and on the way back you need to cruise it for a while at the high end of what you plan to cruise the bike around, get back home, let the engine cool down for 10-15 minutes and then remove that spark plug again and look to see what color the electrode is, if it is a nice medium brown color and the engine was purrring along real nice then I say you are in business, if the plug color is sorta white looking or very light tan you probably need to go up one jet size so that you don't run the engine to lean which makes then run to hot, if the plug color is a very dark brown or blackish color and the engine is blubbering and not purring at cruise speeds then you should go down one jet size and do the test again.

    Hope this helps ya out.

    Map
     
    #2 mapbike, May 27, 2014
    Last edited: May 27, 2014
  3. 2door

    2door Moderator
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    Fischer,
    Where are you getting those jet sizes? I never use or rely on numbered jet sizes. They have proven to be unreliable. I prefer to use drill size when looking for the best orifice diameter. I'm at about 6000' above sea level here in south Jeffco and I've found that jets that have an orifice of between .025 to .027 seem to give me the best performance.
    You must keep in mind that I run my fuel/oil ratio at 100:1 which means I must go leaner on my fuel to air ratio than if using standard 2 stroke oil at 32:1.

    If you're not mixing at 100:1 then I would suggest starting at about .028 for a jet size. That will usually require that you use the solder and drill method of determining the jet orifice size. The alternative is to buy a set of orifice drill bits and find what jet size you have by comparing it to the drill bit that fits the hole. Those published or advertised jet sizes mean nothing to me. They are nebulous at best.

    Tom
     
  4. mapbike

    mapbike Active Member

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    I agree 100%

    I didnt go into bits and drilling jets like I normally do for fear it might be to much for someone not familiar but I agree that is the best route and also the way I do mine.

    Thanks for adding this, excellent advice.

    Map
    .wee.
     
  5. fischer550

    fischer550 Member

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    I bought jets from sick bike parts ranging from 60 to 68, because I assume thats alot easier than drilling/resoldering and all that. Also for oil I plan on using lucas semi-synthetic oil, it does not have a recomended mix.
     
  6. mapbike

    mapbike Active Member

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    Well that is fine, hopefully the jets are correctly sized, I would probably start in the middle with a #65 or #66 and as far as the Lucas oil goes, im gonna say 32:1 or 40:1 will probably work just fine for ya, I was thinking the Lucas is recommended ag 50:1 but I cohld be wrong about that..
     
  7. fischer550

    fischer550 Member

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    You would recomend a 65 for break in on a brand new motor?
     
  8. mapbike

    mapbike Active Member

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    I recommend using the right jet after you determine which one that is by running the engine a short distance and checking plug color until you know that the jetting is correct and the engine isnt running to lean.

    Map
     

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