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Discussion Starter #21
I may try my angle or bench grinder out on my crank when I get home, every bit helps.

Mr Kitty-What about the small windows in the sides of the piston you used in one of your builds, would that help in my case?

I'll clean up my piston and do the knife edge cuts and such before this one goes back together, I did all this to the blown piston a couple years ago, but never started the bike after the new top end until this month (petcock/carb problem) so we start again years later. I'm getting back up to speed on these bikes, things were a little rusty...

The only real mystery on these builds are the exhaust pipes and tuning, I understand the concepts, don't have the software/experience to make my own. I imagine that's the weakest link of my "sum of many modifications together as a whole = power gains".

I'm getting close... thanks for the advise.
 

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It's all about getting it to run lean without blowing up tbh
 

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Discussion Starter #23

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That is looking really good she's going to fly....

After heavy internal modification the stock tin reads work the best.

Fiberglass and carbon fiber reeds work good in a stock engine but after modification there is so much velocity the softer reeds want to flutter out.
 

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Discussion Starter #25
We took the little dirt bike to the trails this weekend! My youngest rode it all day Saturday (5 hrs +). It took someone holding the bike while I pulled gloved to get it started after this build and one last hard pull we split the metal housing. We managed to hold it together and start it one last time.
He got one more ride before returning and stalling, and it maybe giving up the ghost. Looks like the air filter loosened up and sucked up dust for a bit, would that have possibly wore out the cylinder or rings to the point of death?
I'll be able to test compression when our new pull start comes in, hopefully I'll get it up again without having to build it again so soon. Would the typical modified engine not last more then hours of life, I seem to remember reading such, but seems a little low for run time?
The bike was some good fun, my youngster had more fun then he can remember so was worth the time we put into it.
Thanks y'all!
(DR49 in the middle)
 

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Glove puller's destroy wrist pin bearings!

On the CAG 2 strokes they feed throw the crank case that means if they suck dirt it passes throw the crank case bottom end if you think it sucked dirt definitely pull it apart clean and check everything replace the wrist pin bearing (as long as the pin is not starting to turn blue) and slap it back together.

5 hrs is a lot of time for a hoped up CAG engine that's about = to 3 track days I would definitely run it 40:1 to try to extend the life
 

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Discussion Starter #27
Glad to hear we got better then usual life out of it the first good run. I hit the yard hills after break in and the thing pulled me up inclines like a big blke, though the top end only hit 22mph. My son got his first taste of dirt bike fun, it'll only get worse from here, lol.
I'll have anther go at it and hope for the best, maybe I'll luck out and save it. Thanks.
 

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Discussion Starter #28




I think my top end is toast! Sucked a large quantity of dirt and grit into the case when the air filter loosened.



On a stroke of good luck, I did dig up a cylinder and piston kit that I forgot about a few years ago!! Got the exhaust opened up a bit and cleaned up the piston. The bottom end cleaned up nice and the bearings are for the most part salvageable..I'll have it back in business this weekend as the third build on this thing.
 

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that's to bad about the dirt :-( but wow look at the carnage looking at the plug looks like the tune was good :) keep it cant weight to see ver 3.0
 

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Always use high octane fuel and at least 40:1 mix. I always run 95 octane with no less than 40:1. Sometimes 35:1. But also depends on Dino oil or full synthetic.
 

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Discussion Starter #32
I've got a F/C crank for a build, I couldn't figure if that would have been better then the half circle crank that I did the
turbo mod to.. would that have helped the low end?? I'll look up the winged head for next time, here's another I was thinking about

I like the exhaust setup there, is that custom? How about those sliders, is that what I'm seeing? I though about giving our x7 that treatment to save the fairings.
 

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Yes, that's a good choice, looks like the 40mm bore/ 47cc cyld, which is good it has no exhaust relief channel to loose compression, the cyld is thick which so the cyld runs cooler & makes a deeper third port. I would use the stock 47cc stock crank too. Light is the ticket, lighter moving parts go faster, lol. Porting, timing and compression.
 

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Brand new, want to by it, $165 shipped, lol. Very high compression, a rope breaker for sure, lol. It has the new polini lever style flywheel, thats $35 alone. $35 carb, etc, here is the cyld.
 
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