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307 big bore or go with 290

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What big bore kit is the best for MX and a little SX and a little Moutian riding.

45 year old vet B rider and race open B sometimes.

Thanks

2003 YZF250

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how much is the 307 it as im looking for a bit more power in my own bike and who sells/distributes them.

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Reliability can be a factor when you go too big. If the kit doesn't come with a new rod then that's a lot of weight to add the stock rod.

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I'm not sure which kit the 307 is, but it is probably stroked. If you can afford the stroked big bore (like a 302 or 315 Ice Cube) they will have the most power and be the most fun to ride. If money is an object, I believe the 290 from Athena or Thumper Racing is the biggest you can get.

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I'm not sure which kit the 307 is, but it is probably stroked. If you can afford the stroked big bore (like a 302 or 315 Ice Cube) they will have the most power and be the most fun to ride. If money is an object, I believe the 290 from Athena or Thumper Racing is the biggest you can get.

You're the one running the 290 kit from Thumper Racing. I read through some of your other posts about it but didn't find the answer to this question: I I wanted to get the kit w/ the sleeve (having them sleeve it) do they send you a new cylinder already sleeved, and then you send yours in as an exchange? Or do you have to send yours in first for them to sleeve? Do they charge more to do the whole job if you send in your whole motor? LOL, I guess I should just call them and ask all these questions. :applause:

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I called about 290 kit and if you send the motor to them it was like arround 800.00.

New chains were 20.00 or so extra. and it comes with a jeting kit.

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I called about 290 kit and if you send the motor to them it was like arround 800.00.

New chains were 20.00 or so extra. and it comes with a jeting kit.

Don't they sell the kit with the sleeve installed into your cylinder for around $485? That is what it said in their catalogue and that is what they did for me. I don't think you have to send them your whole motor, just your cylinder. They would charge more if you send the whole motor because then they have to do a lot more work than just sleeving the cylinder.

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Don't they sell the kit with the sleeve installed into your cylinder for around $485? That is what it said in their catalogue and that is what they did for me. I don't think you have to send them your whole motor, just your cylinder. They would charge more if you send the whole motor because then they have to do a lot more work than just sleeving the cylinder.

That's what I'm planning on doing. Do they install the piston onto the cylinder for you also?

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That's what I'm planning on doing. Do they install the piston onto the cylinder for you also?

I'm not sure. Are you going to do all the disassembly work and rebuild work yourself?

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I'm not sure. Are you going to do all the disassembly work and rebuild work yourself?

Yep. I'm sure I can manage getting the piston in the cylinder but I've heard it's a pain and I know Eric Gorr usually sends it already installed. I'll probably do a valve job while I've got the top end apart.

One a side note something I thought was weird is that Eric Gorr charges the same if you order the kit and install it yourself or you send your motor in and have him install it. :applause: I figured it would be a little cheaper if you installed it yourself.

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Installing the piston isn't that tough. You just have to take your time and ease it in so you don't bind up the oil ring. When installing the piston, I found it works best to install the piston into the cylinder on the bench, with one snap ring in the pin bore, and then put the wrist pin and other snap ring on the rod with the piston already in the cylinder. This is easier than putting the piston on the rod and then fishing the cylinder down over top of the piston. Good luck.

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