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There is no place for auxiliary ports on these cylinders, you can only wide the port for a view mm on the left and right side.
 

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Mostly if your raceing a CAG it's going to be a stock beginner class so you won't really be able to do internal mods and running a 2 peace cylinder is defentley not going to fly unless they have a CAG modified class.

Most people raceing are going to be running BZM polini balta stuff or other various euro brands

On a side note CAGs are still fun I run mine doing speed runs and parking lot bashing raceing sit down scooters and minibikes and stuff
 

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Discussion Starter #23
When you think about these engines remember that it is just a robin 411 weed eater clone. Robin/Subaru modeled the engine off of a chainsaw.

Almost all of the porting modding flowing and boosting techniques you find here are taken from what's called a hotsaw aka a chainsaw modified and used for chainsaw competition

I have found that by just doing some mild porting and flowing and raising the compression by either dropping the stock head down or shaving the top of a two-piece cylinder will give the engine decent all around performance.

I have found that if you take it too far and go aggressive with porting it will either make a lot of power at low RPM or a lot of power at high RPM with no power in between depending upon how you build the engine.

so you have to really think about things are you building it to run it on a track where you need power coming in and out of turns power for taking off and power on a straight if you are then you're going to need an all-around engine.

Or do you just need low end torque for small parking lot tracks.

Or you just don't care and all you can think about is doing speed runs.

Anyway it sounds like to me you you're into speed runs and if that is the truth then you don't want any boost ports you're going for all out engine RPM big wide transfer ports and widen out the exhaust Port as wide as you can but keep it narrow so that it builds compression fast.

If you're going for a low-end torque you want a boost port you don't want to open up the transfer ports too far when you have a boost Port because you want the boost port to work if you widen out the transfer ports too big then you won't have enough velocity for the boost port to function and you're wasting your time.

for the most part all people need to do to get a good all-around engine is just case match everything and raise the compression and balance everything. For the most part nothing is balanced from the factory and they are shakers stock
HI! Yes speedrun it is. Building and modify the engine is the most fun part for me.
So no boost port you say.
Can you explain why or you found out by trial and error that's the case?

You can get other crankcase to fit a 50 or 70cc malossi cylinder on it.
For now stock cylinder will be used.
What crankcases fit or almost fit?
I don't know of anybody who did auxiliary exhaust ports on a pocket bike engine but hey Im all for the experimentation. These cylinders are cheap. Try the auxiliary exhaust ports and see what happens, let us know.
But yes mild is the best and cost effective way to go. Swapping to a water cooled cylinder is IMO a waste of time and money. Unless you are racing hardcore, but at that point you probably are not using a tool based bottom end.
You will be pleased with blueprinting the case and mild porting to the head. Plus all the supporting mods.
I have a bad 44mm cylinder I think I might try this on. The piston on bdc is visible in exhaust port 3-4mm.
There is no place for auxiliary ports on these cylinders, you can only wide the port for a view mm on the left and right side.
I'm thinking of not widen the main port and get 2 tiny auxiliary ports.
Mostly if your raceing a CAG it's going to be a stock beginner class so you won't really be able to do internal mods and running a 2 peace cylinder is defentley not going to fly unless they have a CAG modified class.

Most people raceing are going to be running BZM polini balta stuff or other various euro brands

On a side note CAGs are still fun I run mine doing speed runs and parking lot bashing raceing sit down scooters and minibikes and stuff
I'm not going to race. Just speed runs and see how fast it can be done

So I've got a bad 44mm cylinder.
I'm thinking of maybe leave the main exhaust port alone for now.
Add 2 small auxiliary ports.
Maybe just raise the main port.
 

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I still say try the auxiliary exhaust ports. Experimentation is where it's at. Definitely try it on that bad cylinder.
I only have one cylinder with one boost port and another cylinder with to boost ports. And the single boost Port cylinder head has a widened exhaust port. The other one is untouched. I mean if you just want to go all out, single boost port widened correctly can be one of the best mods you do and make sure you do a little work to the transfer ports. You can try just doing cylinder head by itself but you should blueprint the case as well. But you should still see an increase in power.
 

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For a higher rpm engine your going to want to cross drill the piston into the transfer ports this does two things it helps re atomiz and spray fuel up into the transfer ports (like a boost port) when the Piston is going down it also helps the Piston anti parachute so It can go down faster then take off some of the Piston skirt which helps lighten the piston and make less friction against the cylinder wall and then knife-edge the rest of the skirt.

the other thing you can do is called a turbo crank modification they do the same on RC boats ( the big ones ) that's where you grind the crank counterbalance and to make them a little bit pointy to help them cut through the air fuel mix resistance.

when building these things I've heard of people knife edging the connecting rod I don't recommend this.

You should replace the stock crank bearings with SKF but if you don't want to spend the money you can use mother's metal polish and stuff the Polish inside the stock bearings and spin them up with compressed air then rinse them out with brake cleaner effectively polishing the insides of the bearings

With these modifications you can get about 12K rpm out of an engine without spending any money if you grind your own rocket key 🙂

I'll get you some pictures out of my other phone later today so you can see what I'm talking about and think about it.

I'll also get you my recipe so you can make your own racing fuel so you can run the thing 😉
 

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Discussion Starter #26
I still say try the auxiliary exhaust ports. Experimentation is where it's at. Definitely try it on that bad cylinder.
I only have one cylinder with one boost port and another cylinder with to boost ports. And the single boost Port cylinder head has a widened exhaust port. The other one is untouched. I mean if you just want to go all out, single boost port widened correctly can be one of the best mods you do and make sure you do a little work to the transfer ports. You can try just doing cylinder head by itself but you should blueprint the case as well. But you should still see an increase in power.
Yes I must try. It may fail but will never know if not trying.
For a higher rpm engine your going to want to cross drill the piston into the transfer ports this does two things it helps re atomiz and spray fuel up into the transfer ports (like a boost port) when the Piston is going down it also helps the Piston anti parachute so It can go down faster then take off some of the Piston skirt which helps lighten the piston and make less friction against the cylinder wall and then knife-edge the rest of the skirt.

the other thing you can do is called a turbo crank modification they do the same on RC boats ( the big ones ) that's where you grind the crank counterbalance and to make them a little bit pointy to help them cut through the air fuel mix resistance.

when building these things I've heard of people knife edging the connecting rod I don't recommend this.

You should replace the stock crank bearings with SKF but if you don't want to spend the money you can use mother's metal polish and stuff the Polish inside the stock bearings and spin them up with compressed air then rinse them out with brake cleaner effectively polishing the insides of the bearings

With these modifications you can get about 12K rpm out of an engine without spending any money if you grind your own rocket key 🙂

I'll get you some pictures out of my other phone later today so you can see what I'm talking about and think about it.

I'll also get you my recipe so you can make your own racing fuel so you can run the thing 😉
Thank you very much.
Pictures would be great 🙂
 

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Discussion Starter #27
Beginning of cag auxiliary ports!
Just drilled a bit. My porting tools are at another location so it will take some days before I can continue with it.
This is the bad 44mm cylinder.
156771
 

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For a higher rpm engine your going to want to cross drill the piston into the transfer ports this does two things it helps re atomiz and spray fuel up into the transfer ports (like a boost port) when the Piston is going down it also helps the Piston anti parachute so It can go down faster then take off some of the Piston skirt which helps lighten the piston and make less friction against the cylinder wall and then knife-edge the rest of the skirt.

the other thing you can do is called a turbo crank modification they do the same on RC boats ( the big ones ) that's where you grind the crank counterbalance and to make them a little bit pointy to help them cut through the air fuel mix resistance.

when building these things I've heard of people knife edging the connecting rod I don't recommend this.

You should replace the stock crank bearings with SKF but if you don't want to spend the money you can use mother's metal polish and stuff the Polish inside the stock bearings and spin them up with compressed air then rinse them out with brake cleaner effectively polishing the insides of the bearings

With these modifications you can get about 12K rpm out of an engine without spending any money if you grind your own rocket key 🙂

I'll get you some pictures out of my other phone later today so you can see what I'm talking about and think about it.

I'll also get you my recipe so you can make your own racing fuel so you can run the thing 😉
Piston anti parachute??? Please explain this, and yes pictures.
How do you make your own rocket key??
 

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That's it just drill ports through the sides of the piston so it lines up with the transfer ports so when the piston is going down it sprays the fuel up into the transfer ports trim off a few mm of skirt then knife edge the inside of the skirt then raise up next to the pin about 1 or 2 mm I also taper grind out the ends of the wrist pin to lighten it a bit

There was a head kit called the killer bee back in the day it had these modifications and the cylinder jug was even powder coated yellow now to get these modifications you have to make them yourself...

Remember when building these engines it's a bunch of small mods that add up doing one big mod is not going to change much of anything
 

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Yeah, its called windowed. Never heard parachute.
To each is own I guess.
I understand how the engines work. I have been taught well. Everything works together. All balanced, lots of little changes for one big ending. POWER
 

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Discussion Starter #34
That's it just drill ports through the sides of the piston so it lines up with the transfer ports so when the piston is going down it sprays the fuel up into the transfer ports trim off a few mm of skirt then knife edge the inside of the skirt then raise up next to the pin about 1 or 2 mm I also taper grind out the ends of the wrist pin to lighten it a bit

There was a head kit called the killer bee back in the day it had these modifications and the cylinder jug was even powder coated yellow now to get these modifications you have to make them yourself...

Remember when building these engines it's a bunch of small mods that add up doing one big mod is not going to change much of anything
Thank you! And thanks for the picture.
I did try the 40mm cylinder yesterday.
Exhaust duration 160°, should have widen the exhaust more I think. And modify the clutch.
It did rev a lot. My tachometer is on the way. But I did not get to the powerband. Clutch engages too soon.
I did install the rocket key and drilled the clutch today so it might help a bit too.
It did rev all the way when doing burnouts.


What about single reed petal? Carbon fiber 0.4mm one piece so the center can be removed from stock reed cage.
Is that a mod worth doing?

Oh and I did crash yesterday, no broken bones 👍 and no damages to the pocket bike. I've got two pocket bikes. One without suspension and that's the one I crashed with. Holes in ground are dangerous without suspension

Sincerely
 

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Thank you! And thanks for the picture.
I did try the 40mm cylinder yesterday.
Exhaust duration 160°, should have widen the exhaust more I think. And modify the clutch.
It did rev a lot. My tachometer is on the way. But I did not get to the powerband. Clutch engages too soon.
I did install the rocket key and drilled the clutch today so it might help a bit too.
It did rev all the way when doing burnouts.


What about single reed petal? Carbon fiber 0.4mm one piece so the center can be removed from stock reed cage.
Is that a mod worth doing?

Oh and I did crash yesterday, no broken bones 👍 and no damages to the pocket bike. I've got two pocket bikes. One without suspension and that's the one I crashed with. Holes in ground are dangerous without suspension

Sincerely
Well, glad you're all right. I remember reading about people trying the one piece some I remember reading about people trying the one piece reed. Some people like the idea but I don't know whatever happened to it there's a threat in here somewhere. If your motor isn't too extreme, carbon fiber or fiberglass will be great. The tin reeds are great for a motor that has been all modded out. Less chance of flutter. I have personally only been using the tin reeds almost all of my engines. Only one has a fiberglass Reed.
CAM2 is who explained to me about using the stock reed for the highly modded Motors. He has been there, done that.
 

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Discussion Starter #36
Well, glad you're all right. I remember reading about people trying the one piece some I remember reading about people trying the one piece reed. Some people like the idea but I don't know whatever happened to it there's a threat in here somewhere. If your motor isn't too extreme, carbon fiber or fiberglass will be great. The tin reeds are great for a motor that has been all modded out. Less chance of flutter. I have personally only been using the tin reeds almost all of my engines. Only one has a fiberglass Reed.
CAM2 is who explained to me about using the stock reed for the highly modded Motors. He has been there, done that.
Yeah I read that too.
I wonder if it's possible to find a single tin reed.
If I found one I will try
 

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I agree the stock engine should of come with a fiberglass reed the tin reed should be a performance part.

There is not enough vaccume to open a single stiff reed all the way and those two stage black widow reeds are junk because stage 1 starts to flutter after about 8k rpm
 

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Discussion Starter #39
I have started to mod the exhaust. This exhaust is not the stock for this bike.
Header will be very short. Approx 10cm/3.95". Don't know if that will be good but that's what's fits the bike.
Don't know about stinger length yet or what diameter.
Pumper carb should arrive in 2 weeks.
156798
 
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