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Discussion Starter · #1 · (Edited)
How-To's: MM64 tips and tricks - Part I

Here's a list of stuff I copied and saved into a word doc. a looooong time ago. See the benefits of searching and saving old writeups from previous cag
tuners? These mod's are still being used by pretty much all the cag tuners.

These tips were done by minimoto64/Scott.

All cag mods
Since some people think there's no info for modifying Cag motors, here's all the mods I've done to my bike, as posted prior on PBP.


Carb porting and indexing- 17 mm velocity stack tapered in to venturi pick up tube. True up 14 mm on the outlet, or 15 mm if you're matching everything. IF you're brave, drill thru with a 9/16 bit. Will leave a little gap either side of the slide, but won't affect operation. Turn idle screw all the way out before re-installing. Index needle, first by shimming. I use a #6 ss machine nut underneath the needle clip, then adjust clip on needle so needleit doesn't come all the way out of the tube @ WOT, otherwise possible stuck needle and you just endoed. Also, sand the needle taper down to more of a toothpick taper. Smooths out acceleration and helps eliminate flat spots. GUT THE CARB BEFORE YOU DO ANY DRILLING/ MACHINING!!!

Intake- match to carb porting and reed block porting with dremel and necessary bits

Reed block- order polini 2 finger reeds, wider but need to be sanded a little around the edges to prevent fouling on the case and screw holes edged in a mm to use on plate. Dremel out reed plate edges to within 1.5 mm of petal edges and 2-3 mm on the Bottom. Sand down reed stopper block from the inside top to the middle, to allow more red travel and maximum opening. IF you can find one piece reeds, cut out middle support and install.

Barrel- With Dremel and tungsten carbide bits, open transfer ports 1.5 mm all the way around. Raise exhaust port 2-3 mm and open 2mm either side. Carry, as best you can, the increased port size throughout the port.

PIston- index by grinding on either side above wrist pin holes, from the top, at an angle, to within 1 mm of top ring groove.

Pipe- cut out header with grinder and remove excess header protruding into diffuser cone and reweld.

Bonus- Take your barrel to any machine shop and have them shave .015-.020 off the bottom of the flange. Compression boost, helps with low-mid range. Raise transfer and exhaust ports to compensate for lower deck height. Check for piston to combustion chamber clearance before starting by rolling the motor by hand. If you get piston strike on the top, add barrel gaskets until the piston clears the combustion chamber.

Disclaimer: If you don't have any idea what I'm talking about, don't even try these engine modifications. I suggest you buy a couple cylinders, as the tolerances from mold to mold don't seem to be consistent. You can do two with no problems and start a third and bust through @ 1.5 mm.

If you perform these mods, you do so at your own risk, and any damage or pretty aluminium ashtrays are your responsibility. I've got a box full, if you need one.

Cag Starter Fix!

Well kinda, Once and if your starter breaks, drill a 3/4 inch hole in the center of the starter housing, then..........you're gonna love this........ put a 1/4 inch socket drive and extension with a 10 mm socket in your cordless drill, shove it in the hole and engage the flywheel nut. Make sure your drill rotation is clockwise, two strokes can run either way, and hit the trigger! You may want to duct tape the socket assembly together so nothing goes flying. I use my drill when I'm bench testing motors and doing compression checks, alot easier than standing on a chair and pull starting.



Cut out the center and open the plate 1 mm all the way around. Leave 1 mm of rubber seal around edge for positive closure and sealing. Buy a set of polini carbon reeds. A little sanding and, BLAMMO! 45% more intake area. Might as well match the intake while you're there!

I used a 8 hp DM. About 2 inches too long but getting ready to cut downand reweld header tomorrow. The above will be my #3 mods you can do yourself thread, in a couple days. I'll try to post pics.


Carb theory
All the throttle in the world.......

won't let the Cag exhale any better. If you look at the port area ratio, transfer to exhaust, you'll see that there's no way the motor can do any better than what you're getting.

Hot gasses take up more room than cool gasses, so you bring in 39 cc of cool gasses heat them to 2000 degrees and they start taking up quite a bit more space, but again port timing and size creates a traffic jam for the burnt gasses to escape, so shiny, new fresh mix starts honking its horn, flipping birds and cussing because it can't go any faster than ole beater, hooptie, black burnt gasses. Freeway is 4 lanes wide at the carb, but theres a 20 car pile up at the barrel, only one lane open. Wait your turn!

Since the carb works on the Venturi principle, whereby a fast moving gas or liquid creates a low pressure area, as it travels across the surface of an object, fuel delivery from the jet to the plenum relies solely on the velocity of the air moving through the carb. You can catually have a higher velocity half to three quarters open than full throttle, since at full throttle you are moving the same volume of air( remember the traffic jam). Given that tidbit, velocity of a gas or liquid is calculated on volume and diameter of the object it is passing through. High volume, small diameter=high velocity. High volume, large diameter=low velocity. High velocity creates a greater pressure differential between the venturi and atmospheric so more fuel is introduced into the air intake stream. Low velocity creates a smaller pressure differential so less fuel is introduced into the air intake stream.

Theoretically, carb design should optimize engine air flow through all rpm's and max rpm's should be reached @ full throtttle, not before. But hey, who said anyone engineered these motors?



IF you're here, you've probably ported your carb and now you're cussing me because your bike is running like crap. Can't keep a low idle, etc. Well , here's your answer. Your bike's too lean. You're getting all that extra air but no extra fuel. Let's take care of that, shall we?

As with #1, your in open class if you perform this mod,so... we're gonna machine our Cag carb to take Dellorto SHA 14-14 jets, so you're not running so lean. Trust me, as we go along you're gonna want larger jets! They come in all sizes and allow you to tune the carb for weather conditions. Here's how we do it.

ITems needed: 10-32 or 6mm-32 drill/tap set, drill bit stop, Hand drill, cresent wrenchs and/ tap T-handle, Dellorto SHA 14-14 jet set. PM me to discuss jetting questions and who has the best prices. I've shopped everybody, I know! Got everything? Good! Lets get started and make some HP!

You will need a drill/tap set, which is a single tap with a cooresponding drill bit, in a shrink pack. You can buy them @ Home Depot. Also buy a drill stop so you don't OVERDRILL! 5-6 mm is as deep as you need to go. I used a 10-32 bottoming tap and cooresponding bit, because that's what I had here. I believe the Dellorto jet threads are 6mm-32. Preorder your jets and take one with you to make sure.

Remove the Carb bowl, don't tear the bowl gasket. If you mess yours, make a new one with a cereal box and a razor knife, x-acto knives work best.

Remove stock jet (brass thing hanging down), venturi pickup tube, (brass thing that other brass thing was screwed into).

Set drill stop on bit for about 5-6 mm. Put bit in drill and drill out stock jet threads in jet hole tube end to drill stop.

With one cresent wrench, hold the end flats of the tube and put tap w/handle in jet port hole you just drilled out. Slowly and smoothly, run in tap with t-handle in hole, one turn at a time, backing off a quarter turn each time, to loosen cutting chips. Not too deep, just like the drill bit! Once you're in 5-6 mm, back it out easily. Blow out tube with compressed air and wash with parts cleaner or similar solvent.

Re-install tube and screw in your BRAND NEW DELLORTO JETS!!!

YEah, you did it!! Congradulations!

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