I think a lot of factors go into how fast you can go. -
The manufacturer of the engine - mine - Powerking
The tuning you have - performance vs. economy.
The overall weight of the bike and it's rider. - bike- Lbs? - me 155lbs
tire pressure - more makes the ride rougher - but much faster - less surface contact.
gas to oil ratio you use - 20 to 1 seems to work great for me.
I read a very comprehensive survey about this, and it seems that once the bike is properly broken in - 32:1 was the best overall ratio for the best speed. After that the horsepower was reduced.
Physical location - I live in a location that is 4,549 feet high in altitude. Like any other engine, I needed to compensate for the thinner air.
Vibration factors - I think more bikes could probably go faster if the vibration was minimized.
did the builder use rubber in-between the clamps? - on mine -absolutely.
How many engine mount points did the builder use to hold the engine in place? - on mine -3
For me, I created a front shock engine mount - which evidently seems to be working for me better than the average HT rider based upon what I have read in this post.
My top speed was 37mph on flat land before I got a little too freaked out.
only once though - you know - just had to see what it could really do.
Don't recommend making it a daily activity.
Another factor might be I have a springer front end that may also reduce some of the vibration on a high speed run.
I have posted articles on the front engine dampener engine mount I made if you are interested in it.
I had been asked if it made a difference - at this point I would have to say _ an ABSOLUTE YES.
If interested just do a search on my name for posts. _ I don't have that many.
Cool to know how other bike are performing.
Couple pic's included to show what I did: - real easy for the cost and benefit.
Troy Fitz.