Would that be this setup here?
http://www.czhfmtransmitter.com/product ... a-kit/2184(This page seems intermittent-- it was working the first time I looked at it..)
I presume you're using the antenna it shows as included with that....?
Just make darn sure you don't turn on that amplifier without the antenna hooked up to it,
or you'll blow the power transistors. Same could happen with the transmitter.
The smaller transmitter is used to drive the power amplifier, with coax from the output of the transmitter to the input of the amplifier.... then the antenna should be hooked up with coax to the antenna output of the amplifier. Both the transmitter and amplifier are going to have separate power supplies. How were you planning on powering these from a bike?
The antenna needs to be outside and in the clear as much as possible, and as high as you can get it. (obviously that may not be much on a bike.) If the antenna is mounted vertically, the transmitted signal will be Omni-directional. (probably the best way to do it for mobile use). If mounted horizontally, the signal will be perpendicular to the antenna, mostly in just two directions.
If you have the antenna inside a dwelling and trying to hear in a car in the parking lot, that could be part of the problem...
I see that the antenna pictured there has markings for frequencies on it-- have you made the adjustments on it to the frequency you are trying to use? Otherwise the SWR will be high, resulting in less signal and could possibly cause damage to the equipment if it is too high. Having an SWR meter for VHF frequencies would be helpful, but I presume you don't have anything like that yet.
If you explain exactly what it is you ARE doing, I might be able to help you figure it out.
Frankly, with so few bikes I presume you won't be spread out too much-- for short distances you really shouldn't need the amplifier, if the transmitter is .2-.4 watts as the web page says...
Are you getting any transmitted signal at all, anywhere?