wondering if you guys can enlighten me if there are any drawbacks to the big bore (considering 351) for trail riding. I am 6 foot 210 lbs, relatively new owner to a 07 250s. I don't know what its like to experience front end lift on this bike , but found that for tough rocky trails the stock power felt good to me, however it would be nice to get a little umph to get the front end up when needed. My plan in to make the 351 the first upgrade (along with the free mods) and jetting.

I hope its not laughable with my size and wt, but is the increase in torque going to make it harder to control in trails or more difficult to keep the bike under control? my thought is no, but was reading an article about a klx 450 with the reviewers complaining about not being able to keep the front wheel down when they needed to. I dont want to ruin a good thing. I love my bike. I just have no frame of reference to go by when looking at upgrading...

Any thoughts would be great!

 

Yes, the added HP and TQ is a huge problem.. More power is never a good thing!!

 

I think this question has been answered about 4 times in the last so many days. I will however give you my opinion again. Keep in mind I never had the 351 so it is just my opinion.

There are 3 different big bore kits-

The 300 which is just a direct replacement of kawasaki parts from a klx300- You use the klx300 piston, rings, and jug. It is an instant 50cc upgrade.
IMO, this is your safest big bore because it uses manufacturer parts that are not modified, and if installed at a dealer should be covered under warruanty.

There are 2 different 331cc kits. IMO, this is the kit that I think most people should use because you get a little more power than the 300 and the cylinder is not carved so deep into the water jackets. If I still had my bike this would have been the way I would have went instead of doing the 300cc.

The 351 IMO is leaning on the edge. There are many guys that have the 351 which will disagree as they have not had any issues yet. The cylinder has to be bored out so far that it almost seems as if the water jacket is almost gone by the pictures which could cause potential issues to those that flogg their bikes or run in high heat areas. You get the most power obviously this way and it is not much more money than the 331 kit. Only time will tell if a 351 will last 5k or 10k miles and how much abuse it can take as it is fairly new.

I had an 07 and I can say this, the pumper carb is a waste of your money in my opinion. All it does is gives you faster throttle responce. There are other things that you should spend your money on first.

Once you start modding your bike, it will be hard to stop. It will start with the big bore, and a jet kit or carb. Then it will lead to better exhaust and air filters, then tuning the suspension and adding better springs which you should do because of your weight. It will help with the front fork dive when braking!

Eventually, it will lead to a **** eating grin on your face, so i say go for it! Either way you have nothing to lose but money!

 

Thanks Buffalony. Think i was a bit wordy last night when i asked. What i was trying to ask was how the power feels on the trails. Would you say that its much harder to control now in certain situations or is it just better all around. Is it possible to have too much power or is that not likely with my size/wt combo. is there enough power to get the front end up with just throttle or is it like that all the time with the big bore? sorry i wrote so much before.

 

To much power??

There is never to much power especially if your over 200lbs riding a 250

The 300cc will loft the tire in first if you pull back a little, in 2nd if you pull back alot or use the clutch to your advantage.

I have never rode the 331 or 351 so i cant say about them.

 

Its better to have enough power when you need it than to not have enough when you really need it. That sounded like a "Deep Thoughts" by Jack Handy....LOL

 

My bike is so powerful now with the 351 that it's not even fun to ride. It's just so fast and torquey!

In the woods I can lift the front wheel over logs and rocks with ease - crap!

It feels so light and nimble, yet it screams like a raped ape - I hate it!

 

If you think the stock power feels good, I would suggest that you experiment with different sprockets which would be a much cheaper route.

After I installed the 300 (292), I didn't notice a "huge" increase in power but I did notice that I was downshifting a lot less. I don't have any trouble keeping the front end down.

You can drop down to a 13 tooth on the front for $25 or less without changing the chain length, and see if that's the "little extra" you need. You can go up on the back too until you get the torque curve where you want it for climbing. I have a 50 tooth for the rear for when I feel like it. I run 14/42 (stock) around town, and 14/50 for the hills. I really don't go anywhere that requires me to go above 55mph, so any gearing is good for me. Getting a 13 tooth front would have been much cheaper than the 50 tooth rear w/longer chain, but it really looks cool with that big sprocket in the rear! The KLX300 comes stock with 14/50 gearing, and when I made mine into a 300, the sprocket and chain were an impulse buy.

 

There are NO drawbacks to the 351 (from my standpoint anyway). A lot of my riding lately has been on rough, rocky, tight trails...uphill and down. Regarding uphill climbing, it is absolutely NIGHT AND DAY compared to the stock 250!! Before the 351 I felt out of control, partially because of not having INSTANT power to increase speed to carry me over the rough rocks, etc. and partially because I had to get enough speed at the bottom of the hill to get me to the top....God forbid I loose momentum half way up, I was screwed. NOW, anytime I need power, whether it be to increase speed on a rocky hill, gun it to shoot me out of a "getting out of control" situation, or to pull my front end up to get over a log, rock, etc., it isn't an issue. I don't know how to express how much EASIER it actually is to ride now!! My girlfriend still has the 250 and she follows behind me. Every now and again, when it gets too difficult for her, I have to go back and ride her's through the rough stretches. Every time I get on her bike to ride it through, "how did I EVER ride with this setup" goes through my head the whole time (no offense stock guys).

The gearing is an option, as I dropped my 14t to a 13t before the 351. That entertained me for about 5 minutes. It was nice that it provided some low-end response where you need it for slow, 1st gear trail maneuvering, but not much else. You just can't compare the gearing to 100cc additional displacement.

As far as longevity, I guess we'll see. As far as I know, I believe CousinLarry is way out ahead of everybody as far as mileage on the 351 goes. But so far, with as many people that have done the 351, you sure don't see a lot of griping about it here (if any, come to think of it). Anyway, for riding the rough stuff and your size (I'm pretty much the same as you by the way), I think you'd be ecstatic with the 351. Good luck....I'm literally off to order my girlfriend a BB 351 kit today for her bike since she got a taste of mine this weekend!

 

Yah, hill climbing with the 351 is one of my favorite things to do

There's an old landfill near me that they don't use anymore so it's just a nice tall grass covered plateau in the middle of a field. You can hit the bottom of the hill in the bottom of third gear, and just twist the throttle and it's instant brutal power screaming up the hill.. It's pretty fantastic