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Discussion Starter #1
Hi! I'm new to pocket bikes and cag engines.
But not to 2 strokes and tuning.

I don't know what the goals is really more than try to get the engine as fast as my knowledge and wallet can make it. And having fun making the engine as good as I can. Some riding too I suppose

I've got 2 engine's right now.
1. 44mm
2. 40mm.

I will go for the 40mm first because the 44mm cylinder are bad. Very much of the top of the piston is visible at bdc.

So 40mm it is.
I have raised and widened the exhaust port a bit. But the exhaust duration is still just 160°
So will make some more work on that.
Transfer ports are really low too so that's need to be raised a bit too.
Don't wanna mess the transfer ports though.


IMG_20200806_210720.jpg
And here is the pocket bike.
It was cheap and not in great condition.
But it's the engine I'm going to do the most work on.

Started porting sorry for the messy shot.
Will make it a bit wider and deeper.
IMG_20200815_174729.jpg

I removed some of the top of the piston to make the exhaust port open fully.
Still using stock carb with petcock mod.


Plan is to continue the porting of the 40mm cylinder.
Lighten the piston a bit.
Make the reed plate a bit smoother.
New bearings and seals.
Pumper carb for easy tuning.
Blue printing of engine cases and cylinder.
Port the crankshaft and crankcase for better flow.
Carbon fiber reed.
Modify exhaust expansion chamber.
Making a 9 fin flywheel.
Lighten the clutch.

What port durations are you guys using?
Is it some basic or advance mod that's missing?
Someone used E85 as fuel?
I've ordered a rocket key, but for a high reeving engine I think I will mount it so it retards the ignition instead of advance the timing, for better overrev capabilities.



Sincerely FutureWorld from Sweden
 

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You can go to ~175° exhaust duration, all more you will loos your exhaust flange.
125-130° should be a good timing for the main ports.
I always stay 1-3° under the main ports with the boost port.
You can wide the boost port to 16-17mm and it should aim into the direction of the spark plug. For the wide of the exhaust port I always take 60% of the bore.
 

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With the e85 I don't think that the cylinder will last for long.
Here is some work that I did.
156700
156701
156702
156703
156704
 

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Discussion Starter #4
Thank you for the information.

Changed the ignition wire to a 8mm silicon.
Did the mod to a stock spark plug connector too.
IMG_20200819_175529.jpg
 

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Discussion Starter #5
@Chrisi I think I will need to buy a new cylinder.
I want to make it a high reeving machine.
Which cylinder and crankshaft would be best of these for power and high revs?
40mm 10mm wrist pin stock crank
44mm 12mm wrist pin crank
44mm 10mm wrist pin crank

Sincerely
 

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I always run the 44mm because the higher torque, so you can use a longer transmission setting.
If got them always near 10-12000rpm, higher then 12k I think you can't run these cylinder. The Hohn structure is worn after 2 running hours, it does not matter if you rehohne them or not.
 

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Discussion Starter #7
Okay. I will try the cylinder when the engine is ready.
Then if needed buy a 40 or 44mm cylinder.
So they can reach equally rpm both 40 and 44mm cylinder? But 44 have more torque?
 

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Yea about 2 or 3 hrs of run time is about what I get but then they seam to run forever in stock configuration just depends upon how far you take them like a race car engine
 

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You need to build an engine like this, Billet Wing Head Cyld Kit & 70 or $80. If you building a 49cc kit, loose the FC crank or buy one without if you can. Get a 47cc/40mm crank and get a 44mm piston w/ a 10mm pin to fit a piston port engine, and put them together. The piston. pin and crank are lighter on 47cc engine. Then modify everything. Most kits come with 3 upper ports and not much cyld for for the piston to ride on. CAM2 held me finish a billet alum cased engine and used a 40mm cyld & teflon piston, with a FC crank cause it has Polini style intake and reeds, with 19mm Walbro 223B purge carb.
 

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Discussion Starter #11
You need to build an engine like this, Billet Wing Head Cyld Kit & 70 or $80. If you building a 49cc kit, loose the FC crank or buy one without if you can. Get a 47cc/40mm crank and get a 44mm piston w/ a 10mm pin to fit a piston port engine, and put them together. The piston. pin and crank are lighter on 47cc engine. Then modify everything. Most kits come with 3 upper ports and not much cyld for for the piston to ride on. CAM2 held me finish a billet alum cased engine and used a 40mm cyld & teflon piston, with a FC crank cause it has Polini style intake and reeds, with 19mm Walbro 223B purge carb.
Hi! I can get a 2/3 piece head for 45 euros.
With 44mm 10mm wrist pin piston.
And using stock crankshaft.

156724


Or a 1 piece cylinder/head 44mm with 44mm 10mm wrist pin piston. For 30 euros.

156725



Or a 40mm cylinder for 14 pounds

156726


None of these kits have a boost port.
But I can add that myself with airpowered dremel tool.


Sincerely FutureWorld
 

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No Billet Winged Kits?? There round head is good but the billet compression caps is better. The cap on the billet head fits over the top ring of the cyld and around so the cap can't move. The round head it just sits on top of the cyld. I many of both. CAM2 was the guy here till his was Banned, most of what I learned about 2 strokes is from him. Him and MrKitty got into a fight over him bad mouthing CAM2 on another site, CAM2 was supposed to, share the Moderator spot will him but got stab in the back. Want nothing to do with him now, you should see his police record, lol.
 

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I bought just the Billet head & cap for $30, then found a cyld with 2 upper ports and ground out the center rib to make one wide upper port, with that you do not need to port the piston. Look at the wide port in the cyld photos from Boosted306.
 

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Got my new 40mm piston. It's a bit lighter than the old one.

New
View attachment 156760

Old
View attachment 156761
All I have to say is it's looking good and you're on track. You were doing exactly what I was taught from CAM2 and EPR. Just keep following what has been already posted on here. I can try to help you along. As I am in contact with both of them still. I am still building a couple engines with their recommendations.
 

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Discussion Starter #16
All I have to say is it's looking good and you're on track. You were doing exactly what I was taught from CAM2 and EPR. Just keep following what has been already posted on here. I can try to help you along. As I am in contact with both of them still. I am still building a couple engines with their recommendations.
Thank you 🙂
 

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Discussion Starter #17
I have thought about adding auxiliary exhaust ports.
Have someone tried that with these engines/cylinders?
 

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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
 

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You can get other crankcase to fit a 50 or 70cc malossi cylinder on it.
 

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I have thought about adding auxiliary exhaust ports.
Have someone tried that with these engines/cylinders?
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.
 
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