What's your poison? Mine is 40:1
If you are looking to mod an engine like the first picture in this post.
Of course if you have a 43cc youll want 49cc but this is just to show the basic mods to giving the reeded engine a lil more kick in all powerbands.
Theres many-many threads about BigBore Kits and what happens if you dont blueprint and rework alot of stuff to get them to work as intended but here's what a basically modded reed inducted cag engine looks like.
MODS & UPGRADES.
Remove Fueltank and Fuellines aswell as Fuelfilter.
Throw old lines and fuelfilter away. Wash out fueltank with hot soapy water and dry out thoroughly. Upgrade the fuellines and fuelfilter to 1/4".
Cost of upgrade, $6-$8
Do The Petcock Mod.
Do a search for this mod. The basics of this mod is to gut the petcock, fill the cavity with JB Weld then when the JB cures drill straight through the fuel inlet through the bottom to eliminate that problem. If you do the mod youll have to buy an in-line 1/4" fuel shutoff valve and install it in-line. Cost of mod, $8-$10.
Velocity stack and HP airfilter.
These items are designed to improve airflow therefore rejetting or adjustment of the c-clip on the needle will be needed to be done afterwards. If a jetkit is needed you can get one between $10 and $20, ebay.
Disassemble Carb and Clean it Out Thoroughly. Make sure the needle tip and seat lip are free of foreign trash and the float height is of optimal height.
1/8" shy of the bowl seal lip is considered optimal float level height.
Replace Tin Reeds to Composite or Fiberglass. Better reeds will enhance flow and offer alot of lowend power. Cost of upgrade is between $10 and $20.
Perform the Reedstopper Mod.
This mod can be done with a grinding wheel and some sandpaper. All you want to do is mod the reedstopper so the reeds open up a lil bit farther but not so far they hit the flywheel.
Cost of this mod. 20 mins time.
JUST AS A NOTE>>>>>>>>>>>>>>>>>>>>
When you do the reedstopper/reedpetal mod replace the gaskets.
DONT REUSE THEM and DONT USE RTV!!!!
You can make new gaskets if your handy by buying a roll of .025": rolled rubber fiber gasket material and with an exacto blade and hole puncher make new gaskets to save time.
Cost of roll
$8 at your local autoparts store.
Aluminum Pullstarter Mod.
An aluminum pullstarter offers alot of pulling resilience better that the stock plastic one. It also helps absorb engine heat aswell.
Cost of this upgrade is between $19 and $25 shipped
HP Sparkwire Mod.
Most coils the sparkwire just unscrews from the coil and one from an automotive set substituted to enhance spark delivery to the sparkplug to give more power and keep the plug cleaner and the throttle crispy.
Cost of mod about $5-8 for a replacement wire if you don't have an extra laying around.
NGK sparkplug BMR6A is the best. BM6A is the normal sparkplug. Plug should be gapped between .030" - .035".
Cost of sparkplug is between $3- $9.
If your no good at rejetting and fiddling around with floater carbs I suggest a Walbro WT series retrofit hp pumper carb kit (or clone). Cost of upgrade is between $49 and $60 depending where you buy from. I suggest this mod 100% because the ease of tuning is so nice. You will need to mod the fuellines a bit but theres threads on how by a member named Jaloos.
Modding ,Lightening of Clutchpads. Crossdrilling the pads to lighten them and adding hp clutchsprings will raise the rpms the clutch grabs at to enhance bottomend takeoff as well as midrange punch coming off a corner.
JUST A NOTE>>>>>>>>>>>>>>>>>
When you reassemble the clutches make sure you deglaze the pad faces and clutchbell with 100 grit sandpaper. A lot ask what clutch is better to buy. Buy a stock type 3 shoe that has aluminum shoes and simply mod them. Keep the stock clutchsprings somewhere safe. Check our vendor supplier section for good places to buy or I use ebay and Amazon.
Lighten the Flywheel.
This can be done as a 12 fin, 9 fin, or even a finger ripping 6 fin design. Cost of mod 20-40 mins labor time with a dremel. I usually use a 12 fin design.
Adding A Rocket Key.
A lot ask if this key actually works and worth doing? The answer is YES!!! The 10 degree advance it gives the ignition timing enhances power alot in every powerband. Cost of upgrade is $10 Theres a thread on how to install it here. How to install a rocket key the easy way
Exhaust System Upgrade.
You can port the exhaust port hole in the exhaust flange and mod the stock exhaust by adding 4-6" to the center section of the expansion chamber using a 2" Id piece of muffler pipe.
The extra length makes a big difference and does it low budget. I have personally done it and it definately has worked great. Cost of upgrade varies on whether or not the mod can or cant be done by you. Here's a thread on the subject. Stock pipe mod
There are upgrade exhausts like IP2, JetPro, Chrome hp style and 1 or 2 others. Cost of upgrade is between $80 to $160.00. Check the vendor supplier section of PBP aswell as the parts for sale section. I use ebay but not a lot available anymore in the way of after market direct bolt in's.
To get better topend speeds you can go 1-2 teeth bigger on the clutch pinion and as low as 13 teeth smaller than the stock rear gear depending how powerful the engine is upgraded to.
Its easier to get a new clutch bellhousing complete with bigger pinion and swap it out.
Cost of upgrade is $20-$25
I Also Suggest if you buy a clutch bell housing complete that you buy a clutch housing with 3rd bearing support.
After basic upgrades your bike will feel like it has more than double its current power. There is ways to get even further powerwise with a dremel set with bit assortment in the way of blueprinting and porting.