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I actually had high hopes of this thread in the beginning. An easy to follow build. I would have thought a budget build would be on a used engine because if I bought a new engine I think my budget would have been blown.
Considering these engines seem fine and balanced already, I think that should have been skipped and the whole bottom end. I probably would have just did the original flywheel mod, clutch mod, reed stopper mod, the base gasket delete. Maybe the carb and cylinder boost port, those two I have never done but would try on a used motor. Still would have made a nice motor IMO.
I did like the quick follow thread with little in between conversation.
Hope you get it fixed. I would love to see a finished product.
 

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Discussion Starter #62
It's a beast man a miner setback and everyone thinks it's bad lol I just rebalanced the flywheel and that's all I had to do !!!!


I used a new engine you can do a used engine if you want I just wanted it to be new so now that it's all finished it's going to last a while you can get them for 40$ to 70$ on ebay if you keep an eye on the price if that blow's your budget that sucks.
 

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It seems that what could have been just a good running engine with a couple early modifications like blueprinting the case and cylinder head like CAM2 always showed us to do. Turned into a repair thread.
New or used engine.

After the CAM2 blueprinting and porting you could possibly base gasket delete, remove six fins off the flywheel, reed stopper mod, clutch arm balance. All "free mods"
After the engine, do the exhaust modification.
All that has been said multiple times on different threads here.
Check out camp345, he has been on a roll with good engine building.

Then if a budget allows Rocket Key, HP clutch springs, spark plug wire mod, NGK spark plug, walbro carburetor or Chinese knockoff.
Then you have one heck of a good Chinese motor, proven time and time again on this forum.
I do hope a new flywheel will fix the problem and see the longevity of this motor especially those polished crank bearings.
 

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Discussion Starter #64 (Edited)
We'll see how long she can last
It seems that what could have been just a good running engine with a couple early modifications like blueprinting the case and cylinder head like CAM2 always showed us to do. Turned into a repair thread.
New or used engine.

After the CAM2 blueprinting and porting you could possibly base gasket delete, remove six fins off the flywheel, reed stopper mod, clutch arm balance. All "free mods"
After the engine, do the exhaust modification.
All that has been said multiple times on different threads here.
Check out camp345, he has been on a roll with good engine building.

Then if a budget allows Rocket Key, HP clutch springs, spark plug wire mod, NGK spark plug, walbro carburetor or Chinese knockoff.
Then you have one heck of a good Chinese motor, proven time and time again on this forum.
I do hope a new flywheel will fix the problem and see the longevity of this motor especially those polished crank bearings.
just remember if you're following Cams build threads that he is building for alcohol-based racing fuels NOT 91 octane boosted pump fuel.

Most of the time I will make my own rocket key I just go to Ace hardware and get a double-wide woodruff key from the Hillman section and use a pair of Dollar store vice grips and use my bench grinder to carve one out.

the plug wire is just stuff that I have laying around I got the Accel racing ignition for my Mazda b2200 drift truck the universal make your own plug wire kit is actually for a V8 all I needed was the shortest wires for my four-cylinder leaving me with the long wires for a Chevy 350 that's basically a lifetime supply of plug wire for pocket bikes lol and on a plus note the boots for the distributor actually work perfect as spark plug boots...

The engine I purchased off of eBay for the project is actually the engine for the mini quad they come with the heavy duty clutch and thicker higher stall clutch springs stock one thing to keep in mind when your engine shopping.

So I have experimented with all three carburetors and here are my findings...

The Dellorto reproduction carburetor is a piece of junk mine cracked and fell off before I could finish testing and tuning it... ( Other members reporting the same problems )

The Walbro reproduction carburetor is definitely a good carburetor the retrofit kit works stellar super easy to tune as long as you get the non-epa version they are definitely not easily rebuildable and once the little diaphragm starts to go bad from either drying out on its own or gets a little help from ethanol blended fuels you basically just throw it away and buy a new one.

Now for the stock carburetor... In stock form it sucks 😜 after modifications it definitely can feed the beast yes a little harder to tune you have to change the jet and raise or lower the needle but on the plus side you can forget you left gas in your pocket bike for two or three years open it up and clean it out and it's as good as new you can basically clean it out indefinitely whereas the pumper carb goes bad with age 😓

One quick note a genuine Walbro will last longer then a reproduction the problem is a genuine one costs more than the entire engine!!!

I did end up rebalancing the flywheel (using a 3D printed RC prop balancing stand that I use for balancing the props for my racing drone) and all is well I might take off the flywheel from the other new engine that I have and modify it in the conventional way but I probably won't...

Ill try to keep track of how many gallons of fuel I run through it get a new RPM/HR meter specifically for this engine and only run it at 50:1 I'm going to try to see how long it can last like you're saying with the polished China stock bearings vs SKF or Timkin that we know easily outlast the bearing in the connecting rod times three!!!
 

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Discussion Starter #65
We'll see how long she can last
This has been a fun thread to follow. I need to try some of this stuff sometime. Hey MrKitty what part of Northern Idaho are you? I'm from Boise currently living in the seattle area, But I have family over by Kellog
I currently live in Coeur d'Alene if you ever find yourself passing through let me know I'll buy lunch.
 

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Discussion Starter #66
Okay understandable. But now you just added more weight to the crankshaft after you just lightened the piston.
Well I guess you'll let us know how it goes.
I have another new engine... I think I'm going to go completely experimental with it.

I'll probably wait until after Christmas but I plan on going more in depth with reciprocating mass, rotational mass and balance factor and why these Robin/Subaru NB411 clone engines are balanced in the way they are to limit their maximum rpm to keep them from blowing up when held at wide open throttle for seven straight hours by an operator doing lawn maintenance.
 

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Discussion Starter #67 (Edited)
I fixed it 😊
what did wrong was I simply got to greedy and tried to increase my balance factor too much on the flywheel !!!

I took the flywheel back off for a third time I tried to drill out the other side and add weight to it to balance it out but I can't because the magnets are in the way.

So I drilled it the other way down into the magnet from the front side then melted some lead into the hole.

Then I drilled out the epoxy on the other side and added re added one of my steel slugs

After careful balancing I jammed a fidget spinner bearing into the hole and sled a screwdriver shaft onto it then spun it up with the air compressor as fast as I could possibly get it spinning holding the screwdriver in my hand just to verify that there is absolutely no vibrations coming from the flywheel!!!!!!

Problem solved and reclaimed the 600 revs that I lost 💪🤯

yes I know it's not all beautiful but you know these flywheels don't last very long anyway because the corners chewed off from starting COG
 

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Discussion Starter #68
Lol this engine is a fighter my clutch started staying lightly engaged opened it up to have a look and found this

this is what it looks like right before the clutch pad delaminates and falls apart
 

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