BT forum pretty quiet for a couple of weeks so checking in on what's up in my world. Tornado last evening missed us by 8 miles, long track mezzo cyclone style which though it lasted about 8 hours did little damage to cities in it's path thank God.
Rode the hybrid Grubee this morning, really nice out. The stock muffler broke off at the can just leaving the pipe. This was a first for me. I had taken the Thrust expansion pipe off and replaced with the old kit muffler in order to run saddle bags to hold my batteries on the rear rack. The Thrust pipe interfered with that configuration thus the pipe switch. The change was noticable on the low to midrange performance which was expected. Not a huge deal but noticable.
When the muffler fell off I decided to just keep riding and see what change, if any, could be felt. I had the GPS mounted, but not the tach. First test was a 10 degree hill, it being the steepest incline inside the city limits. Dead stop at the bottom pulled straight up, not a problem even with the tiny 36t sprocket; no pedal or electric assist. Then off to a flat just outside the city limits for a quarter mile run up to 40mph. I again was surprised at the ease it came up on power band, which I was struggling to get to with the stock muffler just a couple of days prior. I shut it down at 40mph but it was just getting started. This bike with the Thrust expansion chamber has seen mid 50's and with a Mx 80 chamber low 60's. This motor comes on pipe at 5,500rpm to 6,800 rpm depending on which expansion pipe is used and runs out to around 12,000 rpm from a dead stop more than a half mile is required. I'll mount the tach and wear some safety gear to see what he short pipe can reach. I'd be shocked if it actually performs well, but it felt and sounded really good in the cool air this morning.
This 66cc motor is a reed valve, Delloto carb induction with my own window piston and extra port, jug design. Head is a 6cc after market with copper head gasket and a single base gasket. Though I've never dyno test this motor I feel it must be at least 5hp. I base this on how it feels compared to another motor I tested in this frame which dyno test over 8 hp. It was one serious port timed China girl that one day I might rebuild, the jug is all that it needs, but the case needs to be cracked open to remove the debris from the ring that broke.
The current motor has a ton of hours on it and still runs fresh, way past 10,000 miles for certain. GT5 balanced at Bicycle Motor Works seven years ago and shipped as a port timed motor. I'm convinced balancing is a key factor in motor longevity with the CG motors, regardless of the brand. Running an aftermarket aluminum head and avoiding high compression ratio ensures good cooling which is also critical to these motors. Finally running a reed setup with piston window lubricates the wrist pin with a cool charge of fuel extending the motors life as well as helping with power, if set up properly and carefully tuned. Reed systems typically are not just bolt on power; you have to work for it through tuning and testing and this depends on the motor. I have two identical motors set up the same with reed valves one runs really well the other not a lot better than stock. I never went the extra mile to tune the second engine just copied the exact setup of the first. Shame on me that didn't work! It's setting on a shelf as a backup, but if ever need I will tune it properly.
I like all types of motors 4 stroke, 2 cycle or electric and have a lot of good things to say about all of them yet the typical kit China girl requires some real patience and experience to get right on your own. Using a quality vendor like Norm at Venice bikes, for example, is a good place to start.
Rick C.