Here are some mods from ghetto to greatness for adding more tension in case you a broke bitch n got more time than money (we've all looked at that stupid doppler spring thinking meh)
The rubber hose and bolt trick:
Basically get you some 3/8th rubber hose and a bolt then jam in the the spring (be sure to cut the hose so a few mm both top n bottom stick out). I have also used rubber weather stripping wrapped many many times around a bolt for this.
The rubber hose/bolt trick WITH a kickstart spring from shitty scooter:
Same thing as above but get yourself a kickstart spring from some shitty 50cc chinese scooter. Now you are going to remove the metal hook piece and place one end of the spring above the bolt at the bottom then jam the other hook into the bars going to case.
[I am running av7, stock modded head to match bore and decomp sealed, 45mm 74cc parmakit with large base gasket to truely open ports milled down to raise compression, vm18 mikuni carb no filter, streetcup pipe, no head gasket, doppler variator]
With this mod I could lower the weight on the variator and make take-off increased like a mother fucker. Hands down, the rubber hose with this mod is fucking amazing. No more bouncing motor, amazing takeoff and power up huge hills and if your setup is pulling more power than mine then I assume you can get one of the 90cc springs versus the 50cc ones.
Jbots incredible contra spring mod:
This is just a great mod if you have spare shit laying around and can weld. Hell this could def be done in a janky way without welding and is super interesting.
Shock eye welded to bolt, white nylon from a revival shock, Adjustable tension. Welded Pipe guide to stop spring from moving around on frame.
Tested it today, I find that the gy6 springs I had were too stiff, And progressed much too fast to the point of being way too stiff.So I'm using a contra meant for a jog/zuma. They're a lil long, and are a bit less in diameter, with more windings per inch than the gy6 ones. So far so good.
how fucking cool is that shit!!!!!!!!