Madness, Method, and Procedure

Discussion in 'Performance Mods' started by roughrider, Feb 24, 2013.

  1. roughrider

    roughrider Member

    Madness, because trying to get screaming performance out of a motorized bicycle seems kinda silly, doesn't it? I mean, if you really want to go fast, get yourself a sport bike and twist that throttle. :helmet:

    Method, because there is more to performance than top speed. Me? I have a game I'm playing. I'm trying to extract smooth running reliability out of an engine that is notorious for its unreliability. That's the challenge.

    Procedure, because I've evolved a step-by-step approach.

    First, I started with a basically stock build. Then, I got it tuned so that the powerband was pretty smooth and the spark plug was a nice tan for my operating speeds. Right now, I'm still breaking the engine in, so that meant getting the air/fuel mix right at less than 3/4 throttle on the stock, NT carb.

    That accomplished, I then replaced the stock CDI with a Jaguar CDI and a quality spark plug. I have only occasionally opened her up, but I can tell you that I noticed an immediate diminishment of vibration at higher rpms and quite a boost in acceleration from about 3/4 throttle. In fact, even with the 48 tooth rear sprocket, my bike already goes faster than feels safe. I have not even topped her out.


    One problem I have is that the Schwinn style springer forks, even with the brazed in bushings I installed, just don't handle high speeds very well. They are just not strong enough. I can feel it, and I can see them kinda tweaking around a bit at high speeds. I think I need to go with mountain bike forks to get a solid, safe feeling at speeds in excess of 25mph. (Again, I'm still breaking the engine in. I've only ran her at WOT for ten to fifteen seconds at a time. Also, I use an iPhone app to check my speed.)

    Next, I'm gonna mod a spare muffler by installing some undetermined (as yet) number of inches of pipe between the exhaust port and the muffler. I have some flex hose for this purpose, but I'll have to weld some bits of adapter pipes to make it fit nice and snug. Since I'm already happy with the top end, it's the bottom end I'm working on. The bike could still use some more scoot at the bottom of her curve, and given my desire for a reliable little putter rather than a race demon, this seems appropriate.

    I have a Dellorto clone carb I have not installed. Sadly, I've heard mixed reviews. Well, I bought it, so I'll try it. We'll see, but that's for later.

    Last, I was surprised to discover that these HT engines actually are not that loud. I was all worried about the exhaust note, but from the rider's position, it is other engine noises that seem to be the louder tones. Quieting that all down is another project.

    One thing at a time. In the mean time, I'm having fun.

    Last edited: Feb 24, 2013

  2. geebt48cc

    geebt48cc Member

    Hey there Rick,

    Sounds like you are on your way to getting her just right. I bet you got the RT carb , which you're going to love. Just wait till you get it instalded! I've been through all the carbs, and the RT cone has been the best yet. I tell ya, we seem to think alike when it comes to beating all the bad stories about these little china engines. Yeah, uno after the first few hundred miles, start using all synthetic, and get some Castor oil as well to mix with. You only need to mix about 20% of what ever amount of oil you're using to mix.

    Hey, have a good one

  3. roughrider

    roughrider Member

    Hi Glen,

    The carb I bought is a "Performance carb" from JNMotors. Not sure what an "RT" carb is!

    As far as the gas and oil mix... Man, I must have spent an entire day reading all the threads about that. Wow. What a huge amount of disagreement there is on the topic!

    In the end, I just decided to follow the instructions that came in the kit. 16:1 ratio for the break-in, followed by 20:1 with quality synthetic. But I do get why castor oil added would help. I gather it coats everything with a kind of "varnish" that helps with sloppy tolerances while providing a bit of extra protection for when the engine is cold.

    Admittedly, I am pretty clueless about all that. But then, part of the fun with this challenge is just learning new things. Thanks for your thoughts.

  4. jaguar

    jaguar Well-Known Member

    If you want more low end you should add 6" to the header length and make an intake extension.
  5. roughrider

    roughrider Member

    Thanks! From your website, I gathered that your experiments showed it was the 16" total header length that gave the sweet spot, right? Also, I forgot to mention I was gonna try an intake extension too. Cheap and effective. I like that.
  6. jaguar

    jaguar Well-Known Member

    yes but that means 6" additional. the intake extension is what makes the most difference.
  7. geebt48cc

    geebt48cc Member

    Hi Rough,

    Yes, I added the extension that Jag is talking about, and it helps quite a bit. You'll notice much better low end torque. Yes, the RT carb I got came from ThatsDAX.
  8. roughrider

    roughrider Member

    I had a look at the pic on his site. They look identical. Off to Home Depot for some copper tubing and then to the auto parts store for the right diameter hose. Cool beans. I decided to order a spare engine from him, btw.
  9. geebt48cc

    geebt48cc Member

    Yeah, the HT carb gets job done, but the Del cone carb that you've got, will really impress even more!~