Top speed and rpm loss?

Discussion in '2-Stroke Engines' started by danlandberg, Jul 26, 2009.

  1. danlandberg

    danlandberg Member

    I have a loss of top speed and rpm. Low speed and power are good, A little more vibration on acceleration than before. I have changed the needle setting both directions, checked muffler for problems, changed spark plug and cleaned air filter. I have good compression! (Slat head,and tough to start with out skidding rear tire) So far still no difference. It acts like I am in the break in period again 16:1 (I run 25:1, Had it for a few months) I used to be able to hit 35mph + on a good day! Now I'm LUCKY to hit 21mph:( And 4 stroking alot when it reaches its max):icon_cry: Any one have any ideas on what to check next? :confused: Or did I wear it out already? Could I have got the RAW deal:ack2: I have read about in other threads?:veryangry:
     

  2. check that mounts and bolts are not loose,make sure chain is not loose.
    add more oil and go back to atleast 20:1 and see if that works,if that dont work go to 16:1 for awhile.
     
  3. arceeguy

    arceeguy Active Member

    Drop the fuel bowl and make sure that the main jet didn't loosen up and fall off in the bowl. Also check to make sure the needle jet is tight. (the part the main jet screws into. the jet needle is the part you adjust with the c clip)
     
  4. danlandberg

    danlandberg Member

    Thanks C.F. I Was thinking of doing some thing with the fuel/oil mixture next, I Did get fuel from a different gas station last time (there are only two in this town). The thing that got me was, it would start to run better when I forgot to turn the fuel valve on, (until total starvation) carb ran out of fuel. And I am not to sure about a rich/lean mixture. Some say more oil causes a lean condition. To me it would be opposite (checking plug condition)
     
  5. give me vtec

    give me vtec Active Member

    More oil equals lean because there is less gas per drop... thus creating a lean mixture. Less oil equals rich because there is more gasoline per drop. If you just ran oil there would be no gas in the fuel... a very lean condition. A lean or rich condition is in relation to the gas not the oil.

    Sorry if too off topic
     
  6. danlandberg

    danlandberg Member

    A.G. I have two carbs (stock ones). I checked both for any problems (clogging, cracks, ect.) Found nothing wrong. Runs the same with both carbs. I have a GOOD understanding of the workings of engines, (mechanical) it's the oil/fuel & air mixture that has me baffled. It ran for 3 weeks fine on a 25:1 mixture then on the last 1/4 gallon (I mix 1 gal. at a time) I lost top speed and high rpms. I thought the fuel lost its uumff. Got gas at the only place open on Sundays, no change. After riding at fair speeds and power in the higher rpm range I feel like a snail now!! Thanks for the input! DANgerous Dan
     
  7. danlandberg

    danlandberg Member

    G.M.V, I see what you are saying about the fuel/oil mixture amounts. But in the four stroke world lean/rich is the fuel to air mixture. When I got this thing I ran 16:1 for break in and I had to to drop the needle setting one notch to lean it out, was getting to much fuel/oil to air. Doing this allowed more air to fuel. I'm at 5500 Feet asl.
     
  8. QuadManiac

    QuadManiac Member

    He IS describing fuel/air mixture, dan.

    If you have more oil (say 16:1 vs 32:1), there is less gasoline in the same amount of liquid being atomized through the carb while air volume remains the same. Since the same amount of LIQUID is pulled through the jet, regardless of the fuel/oil ratio, more oil means less gas so the air/fuel mixture is leaner. Since the oil doesn't burn, there is less burnable fuel per unit air - leaner mixture.

    Changing your needle changes the LIQUID to air ratio. Only the gasoline part of the combined liquid contributes to the fuel/air ratio. If it is all gas, then it IS the fuel/air ratio (as in a 4 stroke). If it's a percentage oil (as in a 2-stroke), then the fuel/air ratio is a combination of needle setting AND gas/oil ratio and changing either will change the fuel/air ratio accordingly.

    Granted, changing from say 16:1 to 32:1 fuel/oil ratio only makes a small overall change in the fuel/air ratio (about 3% richer between 16:1 and 32:1). Or in stochiometry terms if you were at 14:1 air/fuel it would change to about 13.7:1. BUT this can be enough to make a noticeable change in performance.
     
    Last edited: Jul 27, 2009
  9. arceeguy

    arceeguy Active Member

    Another chap on the forum said he had to solder the main jet shut and re-drill it a couple of sizes smaller to get his engine to run properly at about 4700 ft.

    I don't know why your engine ran so good earlier, unless your weather was considerably colder and your air was more dense? Maybe air density + fuel/oil ratio changes added up to drastically change the way your engine runs?

    Where I live, I am at about sea level and the 66cc engines run a little lean near top speed, but the 50cc engines are fine. In colder weather, both need a larger main jet for best performance.
     
  10. danlandberg

    danlandberg Member

    Q.M. Thanks, It does make sense to me now. But some oil has to be burning (smoke) the more oil the more smoke. I go plug color, lean (white) rich (black). When mine was running good plug was brown. Now it is black but dry. And it does not hardly smoke like it used to at 16:1 during break in. I am going to change float level because there was a small puddle of fuel this morning, I thought the fuel vale was completely off, maybe it wasn't.
     
    Last edited: Jul 27, 2009
  11. danlandberg

    danlandberg Member

    A.G., I have not tried a jet change yet. I went about a block, it would not run worth a poop. I then changed the needle setting and that did the trick! It was new then so I was running 16:1. But I have thought about the air density thing. It has been hot here! When it was running good it was a lot cooler! It's another thing to think about. THANKS!! Dan
     
    Last edited: Jul 27, 2009
  12. arceeguy

    arceeguy Active Member

    Air density plays a huge factor in gas engines. I burnt up a gas leaf blower when I got the "brilliant" idea of using it to blow some snow off of my walkway. It hasd all the symptoms of "lean bog", but dummy me kept on running it WFO. It finally quit after about 5 minutes. Cylinder and piston scored up.

    With your altitude and hot weather, it is no wonder that your Happy Time isn't so happy! I would venture to guess that powersports dealers in your area have smaller jets in stock to keep the equipment they sell running right at that altitude.

    Unfortunately, you kind of have to DIY with a HT engine.

    I have read that Dellorto jets will fit the HT engine. Go to a MC shop and see what will screw in. A #72-75 might do the trick. I need to hog them out to #80-85 here in NJ. Stock is roughly #78
     
  13. danlandberg

    danlandberg Member

    Thanks A.G. In the colder weather conditions, the air is denser. Causing a leaner condition, correct? Moisture has a role to play in this also (I think)? One problem in this town is, it houses just over 2000 people, so there is no real places to readily get such parts. So here it is DIY all the way! OH,! Does Happy Times sell the RAW engine? I got mine off ebay. Thought I got a deal when I opened box "RAW engine, cool". Then I read some threads later (didn't know about great sights like this till later) MY BAD!!!! I have a Dellorto sight in my faves. Just did not know what #jet might help!! In UT, It might take a suit case full, for every other day! They say "If You Don't Like The Weather In UT, Wait 10 Minutes It Will Change" So far in the last couple of days, over cast, but still HOT! I hit 25mph today. Still shy of top speed & mph. Now what?LOL
     
    Last edited: Jul 27, 2009
  14. DJEEPER

    DJEEPER Member

    Do you let it fully warm up before trying to break the sound barrier? :p

    Check to make sure your pipe isnt clogged or anything.
     
  15. danlandberg

    danlandberg Member

    I have checked the pipe, even took the end cap off (a little loud) & as it gets warm to hot, it actually slows down. I know with all the help on this sight, It WILL get it worked out!!! Thanks! I have tried almost every thing (except get a new engine, different brand/maker). That may be next.
     
  16. DJEEPER

    DJEEPER Member

    have you tried adding more oil? It might give you more compression
     
  17. danlandberg

    danlandberg Member

    I Have a slant head, It will skid the rear tire trying to start it until it's warm. Compression seems good!
     
  18. DJEEPER

    DJEEPER Member

    or it might help you run cooler?
     
  19. danlandberg

    danlandberg Member

    It might help it run cooler, True. I have had a lot of 2 stroke dirt bikes and one PUCH moped (in the early 80s). I have not tampered with the oil/fuel mixture to much ( every where I rode in So Cal was about the same climate) no need to, they did good to great (for me)!!!
     
  20. danlandberg

    danlandberg Member

    But I got to say, This thing is starting to upset me! Only because I am a very mechanically inclined person. I have always mixed to suggested ratios, for what ever I am riding, and I have never had a problem with a 2 stroke like this problem!!! "I GOT The RAW Deal".
     
    Last edited: Jul 27, 2009
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