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What's your poison? Mine is 40:1
1,439 Posts
Discussion Starter · #1 ·
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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.
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.
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.
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.

Gearing Upgrades.
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.

What's your poison? Mine is 40:1
1,439 Posts
Discussion Starter · #2 · (Edited)
Automotive lighting Toy Motor vehicle Machine Automotive tire

So you have a cheap 2 stroker bike thats in need of some more power.
Theres no real mystery to it and its quite general for most pocketbike engines like cags and x1's where both have different types of two stroker engines.
This Thread outlines JUST the D.I.Y mods aswell as Basic mods you can do to enhance power. This thread does not cover porting or blueprinting.Theres threads that outline the blueprinting and porting process and requires an attention to detail aswell as a dremel set fully loaded with assorted cutters/grinders.

Change the Fuellines and In-Tank Fuel Clunker.
If the fuel in the tank is old , remove the tank and wash it out with hot water ans dish soap then dry it out thoroughly.
Get rid of stock airfilter and get a velocity stack w/ built-in chokeand a HP airfilter.
Now youre gonna ask where?? Check out the PBP vendor supplier section for more info or ebay and Amazon. Usual cost for a setup is around $20 shipped. I like to use ebay.

There is also a DIY mod utilizing a laundry detergent bottle cap and some pantyhose. You use the palm of your hand as the choke or if your handy can add a choke flap by removing the one from the stock airbox and rigging it to work.
Cost of this Mod, maybe $2 and 30 mins time.

Just know that when you improve airflow intake youll be leaning out the engine severely so therefore some carb tuning may be required. If you have a Walbro carb you have Lowspeed and Highspeed needles screws on the side of the carb that do almost the same thing the same way.
Heres a video for tuning the stock 15mm WYK carb.
.photobucket.com/albums/ww99/CAM2_photo/4 stroke stock carb/?action=view¤t=004-3.mp4

Walbro WT813 HP Pumper Carb Upgrade.
Using this carb will require you use an adapter plate or you mod the stock intake with JB Weld...Cost of this upgrade varies from $32.99-$50.

JUST AS A NOTE>>>>>>>>>>>>
I suggest you using new gaskets between the insulator block and engine aswell as between the carb too. Never trust old gaskets in this area and NEVER use RTV sealants! If you're handy you can buy a rolled sheet or rubber fibre material thats .025" thick to make new gaskets with.

Lighten the flywheel by clipping the fins 3/8" shorter to reduce fin drag and reduce reciprocating weight . Cost of this mod, 30 mins of your time with a hacksaw, sandpaper and a file

Add a rocket key.
Alot ask does it work and is it worth the effort and the money. The answer is YES. Cost of this mod is $10. Ebay is a great plave to buy. You want the LARGE rocket key. For more info about the way to install it heres a thread. How to install a rocket key the easy way

Modify the Clutch.
This is done by crossdrilling the pads, adding hp clutchsprings, deglazing the clutchpads and clutchbell with 100 grit sandpaper and deoxidize/de-rust clutch mount bolt shoulders and mount holes on the pads. When you reinstall the clutchpads make sure you use loctite on the screws.
Cost of this mod, 30 mins labor with a handdrill, some sandpaper, metal polish and of course threadlocker.

Get a quality brand sparkplug.
NGK BPMR7A plug gap is between .030" to .035"
After you reinstall the coil after modding the flywheel/adding a rocket key and modding the clutches it will have to be gapped properly. This is done using a business card that a true .020" thick.
Most use index card shreds but it has to be atleast .020" thick to maximum .024" thick....

DIY Boostbottle Setup.
A lot ask if boost bottles work and worth the effort? The answer is YES.
Theres many-many threads on what boost bottles do and how to make them. Do a search for past threads on the subject. I personally use them and get great results from the ones I've built myself.

Get a Performance Exhaust.
Theres JetPro pipes, rev pipes and fatty pipes for these kind of engines. The JetPro and Fatty pipes offer the best performance gains. Cost of this mod varies by model of bike and is between $50-$100 sometimes ebay has the best deals on exhausts.

Remove the Electric Starter/Generator Battery Wiring Switches.
Removing them has alot of benefits. Here's a thread on the subject. HOW TO: Removing Zenoah engine electric-start w/photos

Change the Gearing.
To gain more topend speeds you can either get a front sprocket thats 1-2 teeth larger or a rear sprocket between 6 and 10 teeth smaller.
Seeings its easier to change the front sprocket I'd go with that.
JUST an ENDNOTE>>>>>>>>>>
Speeds and performance given will vary but will definately give you a noticeable improvement over being bone stock if done right.
If more power is desired I suggest you break out your dremel and learn how to use it well as blueprinting and porting go a long way.

To give credit where credit is due, this was originally a write by CAM2.
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