Herky jerky slow speed cruising?

Discussion in 'Motorized Bicycle General Discussion' started by topgun, Sep 28, 2014.

  1. topgun

    topgun New Member

    Joined:
    Sep 28, 2014
    Messages:
    25
    Likes Received:
    0
    Hello all! New to site, new to motorized bikes. Hope this thread is in the right place.
    I have a Felt Deep six that I love its amazing! I got this bike due to that I love riding bikes!
    But due to year's of abuse on my knees and 4 surgeries later I have not been able to pedal
    Much anymore. My bike is a Felt deep six as mentioned above. The Bike is very simple
    Stock Raw 66cc engine, drive train is basic set up single speed. Coaster break on rear, front
    Break is basic set up no disk. The carb is a stock NT style carb. In frame fuel system. Stock
    Felt wheels, crank and pedal's. I have a 40 tooth rear sprocket. I did not buy the bike for speed but it runs plenty fast as of now. My question is why is the bike so herky jerky upon assisted pedaling to help bike to cruise speed. When low speed cruising there is a lot of slopyjerky motion back and forth. The only way to help smooth out the ride is to either go fast are pull the clutch and coast, are just go WOT. IS THIS JUST THE NATURE OF THESE SMALL BEAST. Is it something I need to get use too, are is there a upgrade, some type of different set up that can be done to help with this annoying jerky motion. Thanks to any and all feed back. I will be looking forward to seeing what you guys have to say.



    ___________________________________________________

    .flg.
     
  2. 2door

    2door Moderator
    Staff Member

    Joined:
    Sep 15, 2008
    Messages:
    16,304
    Likes Received:
    29
    How slow is "slow"?
    Anything under about 10 MPH and you need to disengage the clutch and pedal. It isn't an automatic transmission like your car. The engine needs to be turning fast enough that you don't feel each compression stroke.
    Cruise faster or use the clutch when you slow down under 10MPH and I think you'll have a smoother ride.

    Tom
     
  3. topgun

    topgun New Member

    Joined:
    Sep 28, 2014
    Messages:
    25
    Likes Received:
    0
    Yes under 10mph. That's what I was thinking it was, compression stroke. I do as you mentioned clutch and roll are pedal when cruising that slowly. Thanks for the reply. Just the nature of these machines. Would running some type gearing help? Like for instance Alfine 8 speed hub setup. Thanks again.
     
  4. maniac57

    maniac57 Old, Fat, and still faster than you

    Joined:
    Oct 8, 2011
    Messages:
    4,486
    Likes Received:
    3
    Adding a larger rear sprocket will lower the speed at which you can still cruise comfortably, but you will lose top speed.
    I'd suggest a 50 tooth for good 10mph cruising, but don't expect to break 20-25mph.
    A shift kit will give you both worlds at a cost of course....
     
  5. Mike B

    Mike B New Member

    Joined:
    Mar 23, 2011
    Messages:
    2,256
    Likes Received:
    1
    I had good luck adding a more restrictive (quieter) exhaust. A secondary Briggs muffler and about a foot of half inch copper tubing.

    I think more back pressure helps the low end at the expense of the top end. But since I had no interest in the top end it worked good for me.

    [​IMG]
     
  6. ckangaroo70

    ckangaroo70 Active Member

    Joined:
    May 13, 2011
    Messages:
    766
    Likes Received:
    35
    If speed isn't your thing and you prefer just to putt around under 20mph... you may want to go with a bigger rear sprocket. I built a bike for a neighbor a couple years ago and he had no desire to go any faster then 15mph. He uses the bike in town only to go a few blocks to the Post Office to get his mail and he told me he would like it if he could peddle as little as possible and yet go as slow as possible under engine power. I mounted a 50 tooth sprocket on the rear and he can take off almost from a dead start... or perhaps a half peddle or so. His cruising speed I would guess is probably around 15mph and he can run probably as slow as 7 or 8mph without any bucking. Not much of a tour bike, but it works for him. You may want to play with your gearing some to see what works best for you.
     
  7. Slogger

    Slogger Member

    Joined:
    Sep 8, 2014
    Messages:
    545
    Likes Received:
    3
    Like you I want to go slow and smooth but I'm stuck with a 40 tooth, for now. I am putting on a longer intake manifold to smooth out the lower rpm ranges, although it will cost some top end revs. One dude extended his to about 7 1/2" and liked the results, but his motor had other mods.
    The test data he based it on was the results of long manifolds on a 149cc engine. It's intake manifold was also about 1.2" dia and worked great from 6.3 to 10" long, the longest worked best below 3500 rpm, but going limp at about 5000. This data was from a 149cc piston ported 2 stroke. (similar to the china girl)

    Scaling it down, I'm just going with the length of an offset manifold, about 4" for starters. Anyway, I think a longer intake manifold might help your engine run steadier and stronger at slow speeds.
    Good luck with it!
     
  8. topgun

    topgun New Member

    Joined:
    Sep 28, 2014
    Messages:
    25
    Likes Received:
    0
    This is great, truly a wonderful wealth of knowledge. These past helpful post are all great! Not into the speed on this little gem, I got it to just tool around on in slow motion. Not looking to break any land speed records on a bicycle to each his own, nothing wrong with that. Larger sprocket and shift kit sounds awesome for my ez go attitude on my China Girl. I get my fix for speed with a big block Blown alcohol injected Hemi in my 1800 lbs Drag car. The restricted exhaust also sounds like a plus on the bottom end! Thanks for the knowledge guys! I know that Norm can help me with anything but I'd rather not bother him too much, he's very busy and I would not want to bother him with such trivial questions as gearing. He already thinking over engine upgrades for me. Thanks again and have a great night you guys!





    ___________________________________________________
    usflg
    VMB built Felt Deep 6
     
  9. topgun

    topgun New Member

    Joined:
    Sep 28, 2014
    Messages:
    25
    Likes Received:
    0
    Longer intake also sounds like a good idea for smoother low end cruising. Thanks for that aswell!
     
  10. Slogger

    Slogger Member

    Joined:
    Sep 8, 2014
    Messages:
    545
    Likes Received:
    3
    You're welcome, TG, but I got mo'.
    The standard CDI's are set up for full advance spark timing, no curve. If money is no big deal, there are very cool CDI's to be had that retard that timing at low speed, this would make a huge difference.
    This is a cool thread, if anyone knows how to get more lug power chime in so we all have the info.
     
  11. topgun

    topgun New Member

    Joined:
    Sep 28, 2014
    Messages:
    25
    Likes Received:
    0
    Timing advance and retard capabilities sounds like a winner to me! If you are anyone might know of the right part for the job please chime in. Money is not a problem I love really nice toys and I'm willing to pay for it, not bragging I'm not rich but we are comfortable. I just want my little china girl to be exactly as I want her to be and do everything I ask her to do. Sounds kinky but don't take it that way! LOL
     
  12. topgun

    topgun New Member

    Joined:
    Sep 28, 2014
    Messages:
    25
    Likes Received:
    0
    Timing is a great idea!! Did not realize it was full advance all the time. Yes I do have stock electronics I'm sire. What brand do you recommend. Who might have the part on hand? Thanks again for your time and knowledge!
     
    #12 topgun, Sep 29, 2014
    Last edited: Sep 29, 2014
  13. Slogger

    Slogger Member

    Joined:
    Sep 8, 2014
    Messages:
    545
    Likes Received:
    3
    I haven't tried the custom CDI's but they are out there. They also use a better coil. You can just upgrade the spark wire on the stocker from any auto parts store.
     
  14. Slogger

    Slogger Member

    Joined:
    Sep 8, 2014
    Messages:
    545
    Likes Received:
    3
    I can't vouch for any particular brand, some members haven't gotten good results from the ones they tried so I think you're better off reading up through old threads on here and deciding if you want to go that route. I know the kit CDIs are very basic, so there could be some improvement there.
     
  15. motorized kodiak

    motorized kodiak New Member

    Joined:
    Aug 3, 2013
    Messages:
    105
    Likes Received:
    0
    hey guys, what is back pressure? is it important?
     
  16. Mike B

    Mike B New Member

    Joined:
    Mar 23, 2011
    Messages:
    2,256
    Likes Received:
    1
    Back pressure is created by a restriction in the exhaust stream. At low RPM it helps a 2 stroke by keeping the fresh charge from blowing out the exhaust port.

    At high RPM it causes the exhaust gas to remain in the cylinder. So it helps the low speed performance at the expense of high speed performance.

    I have added a second muffler to a lot of my bikes and I can tell you that it does work. The motors all made less noise, idled smoother and would run smoother at low speed.
     
  17. Davezilla

    Davezilla New Member

    Joined:
    Mar 15, 2014
    Messages:
    2,708
    Likes Received:
    3
    Another idea to think about is adding in a reed valve kit, that'll give you better bottom end performance with less top end loss. The advantage of the reed valve is there's no blowback at lower rpm's and once the charge enters the case it can't back out into the intake manifold or thru the carb so there's also a fuel efficiency gain that comes with it. The kits they sell at JNmotors and a few other sites will do just what you want since you're not looking for top speed, there are bigger and better reeds available for the screamer engines, but the RSE reed kit does really well for smoothing out a rather stock engine... http://www.jnmotorsbikes.com/product_p/jnm1252.htm These also work really well when there's no room for a longer intake and for a nice clean looking install with the carb in almost the stock location.
    These will lose a little power on top but not as much as other mods can.
    If you need to keep the price down tho, adding length to the intake and exhaust pipe can get you similar results, you can actually tune your engine to make the best power at a certain rpm by changing the length of the exhaust pipe or intake manifold, or both.
     
  18. topgun

    topgun New Member

    Joined:
    Sep 28, 2014
    Messages:
    25
    Likes Received:
    0
    Sounds great! Anything to upgrade my ride. Got to have the best of everything no exceptions. Got the parts for a three piece crank setup today. Gonna work on install tonight as long as Baby girl allows me to. Thanks again!


    usflg
     
  19. apex

    apex Member

    Joined:
    Aug 27, 2013
    Messages:
    62
    Likes Received:
    0
    Two things I didn'tsee mentioned yet that can affect low speed juddering are as follows

    1) Chain tension. A slack motor-drive chain can be a factor, as it can "wind up" and then slacken, causing a jerky motion that can feed into itself or resonate, so to speak.

    2) The stock nt carb doesn't seem to have great low speed drivability, in my opinion. I upgraded to a $30 rt carb/filter and got much better off ide drivability. No more 4stroke patches as you run up the rpms, no hesitation. The top speed seems about the same, but the low-mid range is just better. I attribute some of that to using a proper jet (#65 for me). The rt seems to be a dellorto clone, so getting proper jets is cheap and easy. This is based on my opinions and experiences, others may differ.
     
    #19 apex, Sep 30, 2014
    Last edited: Sep 30, 2014

Share This Page