I have been researching big bore kits for about 3 months now and have learned alot from this forum. I know the 351 questions may have all been asked by now, but I have one I cannot seem to find the answer to.

First off, I have 1900 miles on my bike, and 1700 miles are on road. There is almost no off road riding in southern wisconsin. So, if I go with a big bore kit like the 351 can I ride at 60-65 mph for an hour or hour and a half at one time. Last fall I rode 140 miles in one day between 45-65mph. Would the 351 be able to handle this or is the 351 mainly for off road use at lower speeds.

Most of my rides are about 40 miles in about 1 hour. I like to ride the country roads. I know the klx250sf is street use only and is geared differently so it may not be a problem. My bike is stock gearing.

 

If you keep the KLX mainly on the asphalt and are going to put a 350 on it you should bump also the chain sprocket from 14 to 15 . Either way I would change at least the air filter snorkel .
As my KLX 250 is now ( cam mod , air filter lid removed , changed the exhaust "butt plug" ) it does a cruising speed of arround 100 KPH ( 60 MPH ) at 1/4 throtle and it can quickly accelerate to 130-140 KPH ( 80 - 85 ) for quick overtaking . My gearing is stock ( 14/42 ) and I´m not going to change it because I use the bike more like 50 - 50 on and off road .

 

Why wouldn't it?

 

I ride an SF with the 351. I do indicated 65 all the time. I went up on the front sprocket to a 15. It turns 6,000 rpm at 60 mph give or take. No problems. The bike is right in its torque curve so when I crank the throttle it wants to take off.

David

 

HI! The 351 would actually be better for long distance cruising, as it produces more power in midrange and you dont have to rev to higher rpms to sustain highway speeds.. the 351 also doesnt really operate at high rpms so it turns the klx into a tractor..

 

If you leave the gearing alone it will turn the exact rpms at whatever speeds you are at as it does now. That will only change with a gearing change. And you can still run the bike just like you do now, it will just have a little more pep.

 

Exactly. My stock-geared 2009 turns 6000 rpm at 60 mph indicated. It's actually how I know I'm in 6th gear...the rpms are 100 times greater than my speed. 4500 = 45 mph, etc. My bike will run 70 mph indicated up the steepest of hills around here.

It just depends upon what you are looking for, but, the 331 or 351, etc., will run faster than the 250, unless you are redlining the 250...at any given rpm, the speed will be exactly the same no matter the displacement.

 

Thanks for the info, but why go to a 15 tooth sprocket on the front. I know it will lower rpm's but I'm not looking to go fast.

 

I don't know, that's why I'm asking. It seems like most people do more off roading then on road. Therefore the speeds would be way down.

 

Thanks