Big bore kits

[motodude1958]

Does anyone have much experience with Yamaha 250F big bore kits? I'd like to know what would be a good kit like 276 or Athena 290, I'm concerned with reliability and losing all my top end power, but don't want to spend a fortune.

Any suggestions?
Thanks,
Jim

 

[woodward_259]

I heard really good news on the Athena 290 kits. I havn't actually had 1 before, but I heard they make good horespower and are suposed to be the most reliable kit out there. If I was going to get a big bore, that's what I would go with.

 

[Sawblade]

Do a search for Athena 290 kits and you will find a good thread or two about this subject. ;)

 

[Patman]

Why do you want a big bore? That might be the most important question to answer forst. Next what do you want out of it? More bottom/mid/top/everywhere? What kind of maintenance habits do you have? Another REALLY good option would be Eric Gorr. Rich has built several 262's that people rave about and they also did a 284 for my XR that rocks :aj:

It's not all about big names or displacement a lot has to do with the total package which might not be part of any "kit".

 

[Rich Rohrich]

The Athena makes great low-mid power for a really good price. When you look at what some companies are charging for the incredibly overpriced 302 kits the 290 Athena is a real bargain.

The downsides to the Athena are, the engines run out of air at high rpm so they flatten out really early compared to a stocker unless extensive head work and cam changes are done. Even with work they just can't rev like a 262 or a stock bore engine. The other problem is that big 290 piston is really HEAVY compared to the OEM piston or a 2mm oversize (262 cc) . This puts a lot of extra load on the crank, rod and main bearings.

You can't put a 290 kit on an engine with tired crank without risky putting the rod through the cases at some point. Even with a new crank and rod, their life span will be significantly shorter with the 290 kit.

Even with those considerations the 290 has proven to be a great kit for a lot of riders.