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Discussion Starter #61
Tested it again today. I cut and shortened the pipe and made some other adjustments and this was the result...

159478


The purple curve is the one with the long 820mm exhaust. Promising rev capability but little power.
Then blue curve with the original 725mm(ish) exhaust length, finally 4HP and pulls a lot harder. Sounds crazy as h*ll :D
And the red curve after I modified the combustion chamber, 4.2 peak hp and even more high rpm power. It reved to almost 14800 in the curve, and it sounded like it still would have got more.
I can imagine how the bike feels to ride now. Right from takeoff there is 0.5 horses more than previously :sneaky:

Regarding max rpm, still 1200 to go to break CAM2's rumoured 16000rpm (presumably with nitrous/alcohol and no proof of it). And yes the bike is running pump gas, 98 octane.

The combustion chamber modification was to machine it a bit larger because the plug was shrouded in the hole. After machining looks like this

159479


Apparently less compression ratio can give better power. It can be due to the exhaust pipe getting more heat (smaller compression ratio leaves more heat that didn't convert as pressure on the piston) . Other possibility is that the combustion chamber shape was simply bad before, as the plug was about 2mm inside the hole.

The mad bike, removed the head for machining and checked inside cylinder that all is ok

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Cylinder looks perfect now and no detonation marks but we will see how long...

159481



The bike has now a problem with the carburetor. It only pulls with the choke on. I tried to put a 98 main jet but that's still too lean. I think it is caused by my stupid idea to drill the air jet hole previously, trying to fix the problem. I need to somehow resize the hole with a plug.
Then my CDI fried again. Apparently the RPM is a bit too much and need to revise some part of the schematics...
I think there is still significantly more power to be had by fixing the carburetor issue and fine tuning the ignition.
 

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Great numbers.
That's a high reeving weed eater engine 馃槈
Too bad the cdi broke.
Look forward to hear it run when cdi is fixed. 馃檪
 

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Any thing mutch over 14K and you risk the flywheel grenading 16K is very unrealistic even with racing fuel or nitrous...
 

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Discussion Starter #64
Does someone know examples where the flywheel has exploded? I have thought about balancing the flywheel separately of the crank, and also sanding smooth the flywheel surfaces. That should help prevent it from cracking. I made an extra metal shield over the top of the cover but still it's scary to sit close to the bike when doing dyno pulls :D
 

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I have never seen it happened to a pocket bike engine personally. I did see it happen on a go-kart and a Jeep the Jeep flywheel grenade was really dangerous cuz there was a lot of spectators it could have killed people...

anyway a lot of weed eater and small two-stroke engine manufacturers actually print a burst warning onto the flywheel.
 

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According to the seller's website it's possible to install 33mm or 35mm stroke crankshaft without modifying.


Im a bit late on this one but i actually ordered some fcc's from avotecnica together with my 70cc cag engine that is sitting in my dirtbike,

But those fcc's are no better then the chinese ones, they are not very precise, you should try to find the fcc from bidalot which is a very good european tuning brand like malossi and polini. I measured both and the bidalot ones are very good when looking at the build quality and precision.

If you want i still have 2 bidalot cranks laying around and im willing to sell them for a fair price if they are discontiniued.

You do need to put them back together as i pulled them out eachother because i wanted to give it more stroke but then realized that it isnt possible (facepalm!)



Verstuurd vanaf mijn SM-G960F met Tapatalk
 
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