Clutch engaged clutch. then loose 1/2 my rpm at full speed?throttle.

Discussion in 'Transmission / Drivetrain' started by WINDY CITY BOB, Aug 3, 2016.

  1. When clutch is disengaged my motor screams! Once I let IT out I start off slow (because I have a 30 tooth sprocket.
    Still,,,,, when I reach top speed I'm only. At around 1/2 of full RPM??? Too small a sprocket?

  2. FurryOnTheInside

    FurryOnTheInside Active Member

    What is full rpm? Which engine is it? 66/49? Grubee or generic one? Some say (and I believe it, and am designing around it, but haven't run yet) that the engine will last longer, have less chance of catastrophic bearing failure miles away from help, if the RPMs are kept low, like maybe 4100 cruising speed. Obviously that has to limit power but I don't mind that personally, only wanting a bit of help to get somewhere and not being bothered about the power that I "could" be missing.
  3. crassius

    crassius Well-Known Member

    yes, sprocket too small - on most motors one would need to weigh less than 90lb for a sprocket that small
  4. Its a 49 CC generic I don't have a tax so I don't know RPM However it does very high and expecting that it runs at full capacity whatever that may be 6000? I really don't know what the highest RPM is but it runs at full capacity with the clutch disengaged.
    I knew I would lose power off the start and I have to pedal a little bit off the get-go to get moving sometimes. Currently the plug I am using is an iridium BPRH7HIX Just like the LG K7 it works well at around 70 degrees at night I live in Chicago and it gets to about a hundred degrees with the heat index in the humidity , Regular air temperature is that around 90 degree High eighties and nineties, . I get much much greater speed but at night time when it drops down into the seventies it could be in the mid-70s That's when I get balls to the wall speed.
    I have a stock CD and whatever I put on a standard Automotive spark plug wire. Tired of having you take the nipples off of all these nice spark plugs that I have bought. I have also tried to NGK BPH5,6,7 In the southern works the best I even tried the lower ones during the day and no good no bueno. Single or I want the worst performance I got I also have been using an E3.22 plug it works just as well as. The iridium, & NGK 7 .
    I would like to be able to eat it one more tooth to my drive sprocket on the engines because for every Tuesday at 2 that is like Removing 5 teeth in the back. I don't know if that's possible on this engine But I was talking to a friend who used to be a pro racer and he told me that about the gear ratios front to back. If I could do that and then go up to a 36 tooth rear sprocket I'd be where I'm at but get more torque So that's what I'm working with right now if you have any other questions feel free to ask me and share what else on the other knowledge you have with me please thank you
  5. FurryOnTheInside

    FurryOnTheInside Active Member

    I think Crassius got it. Idk how I skipped past that bit but a 30t rear does seem way off the scale for a 26" wheel. There's definitely a 34t available from a few places.
  6. I can get any size sprocket I want from 30 all the way up to32, 36, 38, 60 48 50 and 52.
    any even numbers I have mags
  7. FurryOnTheInside

    FurryOnTheInside Active Member

    Can you find an online gear calculator? If you have a speedo you should be able to figure out your engine speed from your road speed and try a few hypothetical gear ratios. You will need your (loaded) rollout to be truly accurate but it would still be interesting to see, even if not entirely accurate the differences between the gear ratios will be the same IMO.

    It is a pity no one is making a top hat adapter for the ISO disc mount that is drilled to take ordinary bicycle chainrings. We could have UNeven numbers then and people outside the USA wouldn't have to pay the huge amount for shipping.
  8. IMO? (Loaded)rollout? I'm still pretty much a newbie here sir LOL SORRY
  9. FurryOnTheInside

    FurryOnTheInside Active Member

    In my opinion IMO
    In my experience IME
    I can't remember ICR
    If I remember correctly IIRC
    As far as I know AFAIK
    I can't be arsed I CBA :D

    Loaded rollout - sitting on the bike and rolling forward one revolution of the wheel for accurate real world tyre circumference, rather than relying on the nominal 26" measurement.
    WINDY CITY BOB likes this.
  10. How does a tach connect to a engine anyways I have no idea how they work how they connect to the motor and calculate the RPMs to that dial Where do the wires go?
    I mean I understand the gear ratio chart a little bit and stuff like that but, There are just some terminology I just don't understand and some techniques I have no idea what they are? I'm one of those jack of all trades master of none Guy's.
  11. FurryOnTheInside

    FurryOnTheInside Active Member

    KCvale was telling us recently about one he uses that just goes against the spark plug thread. Fabian figured out a way to use a bicycle speedo mounted on the jackshaft sprocket.
    I am sure with a single speed bike you can figure out RPM from road speed with a bit of maths or a gear calculator and then just remember what the rpms are on your bike at certain speeds, or write it on a chart and stick it to your handlebar stem.
    WINDY CITY BOB likes this.
  12. As long as we're on the subject of ratios and stuff like that, since I have a 49cc if I were to an 80cc? Would that give more power more speed or both or neither? Because I have another engine kit exactly the same as the one on my bike still in the box.
    Thinking of maybe selling it and making a bike for speed only, a racer if you will.
  13. FurryOnTheInside

    FurryOnTheInside Active Member

    From what I read here I understand it like this...

    The 49 is supposed to be smoother than the 66, because it is basically the 49 bottom end that we get on both engines, with just minor changes AFAIK.
    There is a saying "there's no replacement for displacement" certainly a larger engine should produce more torque and power, all things being equal (ATBE). Whether it holds true in real life (IRL) depends on the things that are not equal. Such as the upgrades you can do, spares availability both of which favour the 66, and the bottom end and associated vibration problem which favours the 49.
    I would say 66 for torque, acceleration, pure grunt. 49 for smooth high speed on open roads.
    I made my choice based mainly on the available upgrade parts and the wealth of knowledge and information on the forum, plus the fact that I want to run low RPM so I need the higher displacement.