Bike won't go faster down hill?

Discussion in 'Frame Mounted Engines' started by mikesbike, Jul 6, 2007.

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  1. mikesbike

    mikesbike Guest

    Does anyone have ideas as to why my bike won't go faster down hill? It acts like there is speed limiter. I have a 48CC motor on a 26" crusier frame and 44 tooth sprocket. My motor runs well. It has over 2000 miles on it. It goes about 26-27 mph top speed. I got it to 33 once, don't know what was different that day? But the wierd thing is that it won't go faster down hill. One would think that it would speed up but the engine holds it back. Why is that?

  2. IDK, maybe it's just an engine braking effect that wont allow it to go any faster.

    What happens if you pull the clutch in while going down hill?

    Just a thought:
    How fast can these engines safely spin before they shoot a connecting rod out the side?
  3. Herrmanator8

    Herrmanator8 Guest

  4. srdavo

    srdavo Active Member

    I agree...sounds like normal engine braking to me.

    I think redline on these happytimes is around 6000 rpms.

    try this....but be big is the hill & how fast do you wanna go?
    did I careful?
  5. quarkdude

    quarkdude Guest

    I have tried this also and it seems that the gear ratio from the front sprocket to the rear sprocket and the engine rpm being at or near the max rpm that the motor can deliver causes a limited speed going down hill. I also have pulled in the clutch going down hill with the motor at max rpm, and the bike itself will go faster. Be very careful if you do this because if you re-engage the clutch at a higher speed than when you pulled it in the engine braking kicks in and it feels like you might go over the handlebars or, like me a scary fish tail action at high speed can happen. If you put a bigger sprocket on the back wheel ( like a 52 tooth or so) you can increase your top end if you want to go faster however the low end will suffer on torque a little bit. I haven't done this but it is something I would like to try sometime.
    ..........Thanks, quarkdude from Albuquerque, NM
  6. gone_fishin

    gone_fishin Guest

    if you "coast" down a hill with the clutch engaged, you're rotating the engine but depriving it of the lubrication it needs, also (my opinion here) if you keep the throttle open but are maxxing out, you're very likely subjecting the engine to a super-lean condition, also not to dis-engage and be a regular bicycle 'til you get back down to a speed the engine can handle...

    (quark, you have it backwards...larger sprocket=more torque=lower top-end)
  7. bamabikeguy

    bamabikeguy Active Member

    Mr. Albuquarky,

    You are going to fit in here just fine, excellent post.

    fyi- w/ centrifigul clutch, I go down the steep hill below the driveway, hit 43 by the bottom, do 28 on the climb back up, according to my neighborly digital speedometer timers who follow me.


    except for the backward part :grin:
  8. srdavo

    srdavo Active Member

    good info quarkdude......
    except for the bigger sprocket info.... a bigger rear sprocket gives you more low-end torque & less top speed.
  9. gone_fishin

    gone_fishin Guest

    beat ya to it again :p :p

    now, quit it guys...i'm supposed to be going to beach cruzin's place to, as he puts it, "kick some motoredbikes around"...actually we're gonna work on 3 different ones (mostly intake leaks as usual) and we'll try our best to not kick any of 'em :lol:
  10. srdavo

    srdavo Active Member

    shhhhhhhhhhh :lol:
  11. azbill

    azbill Active Member

    when I hit a steep hill, I dis-engage the clutch, but blip the throttle a few times to keep lubrication happening (if it's a long hill, I turn engine off)
    then I wait till I slow down enough to re-engage without putting too much strain on clutch
    feel free to correct me if I am wrong...I would rather be corrected than damage another engine
  12. quarkdude

    quarkdude Guest

    You guys are correct, I stand corrected about the rear sprocket size versus low end torque. Great idea to rev up the engine a little while coasting down hill.

    Do any of you guys need to re-jet your carb? I will put together a short how-to soon with pictures if I can get time to take them. Pretty easy to do and has been working flawlessly on my bike for over 6 months now.
    ...........thanks, quarkdude
  13. srdavo

    srdavo Active Member