331 would probably remain cooler in the hottest desert months in Southern Nevada. I see the 351 sleeve encroaches ever so slightly on the water jacket openings...but, as someone that has worked with fluid dynamics most of my professional life, I don't see this as a signifcant obstruction that it would actually decrease flow rate of the coolant.

Be safe and stick with the 331? Maybe go 340 (partly for the novelty of it...I know of no one that has the 340!). Or, "Go Big or Go Home" and trust the 351?

I do have a Thermo-Bob already on my bike, so, the coolant temp will at least warm up more quickly, and stay more stable. With a coolant change to the "water-wetter-type", maybe the 351 is no concern. I just want to make sure I don't compromise reliability, as I sometimes venture out in the desert alone...and that can kill you if enough bad things happen all at the same time!

Going to stay stock carb for now...I'm not a racer, just a desert explorer that likes to go quickly from time to time....OK, most of the time!

 

If you are going to do it, go big! There are some additional means of coolant if that is a concern for you. You can always add water wetter to a 50/50 coolant mix that should also help in keeping temps down.

 

If there were going to be head gasket problems, I think they would be showing up by now. Also, if I were going to be holding it pinned wide open a lot, there might be a different consideration. In reality, the extra torque of the 351 at lower rpms would simply be nice to have, and I wouldn't be wringing it's neck very often anyway.

Still have to do Suspension upgrades first...if that comes out really nice, and if my new seat comes in and works out really nice, it would be more compelling to go 351....because I'd use the bike for more of my rides. As it is now, I ride a KLR650 when I must tool down the road a bit, or, if I'm going on a LONG ride...as it's just a lot more comfortable than the KLX....the KLR is just more work to get through the tougher spots.

Who knows...a re-suspended, re-seated, 351 KLX might make the KLR a "mostly road ride" kind of bike, which would probably be more appropriate for it's size....but, I've been squeezing that big piano through all sorts of trails. The KLR can do it, just not with aplomb. The KLX in stock form already out-performs the KLR on those goat trails I find myself on out in the desert on the side of a mountain!

 

Bigger = more power anyway you look at it. Im wondering if they are going to come out with something bigger cause Ill get that one.

 

B58, the cooling system on the KLX is darned good...seems to have some overkill built into it. I have a Vapor instrument panel and get to see the exact water temp under all conditions. Compared to my KLR600/650's over the years, the KLX runs stupid cool. Remember, our later generation 250's really started life as 300's, and 300's don't even have a fan. So you're really only adding about 50 or so cc's. I kept mine as a 300 only because I got a really cheap price on the Kawasaki kit. I wouldn't hesitate to go 351 otherwise.

 

Logically, I think the 351 will be OK. My gut tells me not to get greedy...and stop at 331. If I didn't ride when it's stupid-hot, and if I didn't go far out in the desert like I do, I'd go 351 without blinking.

I'm also sure the cooling system is "overdone", and added a Thermo-Bob for that reason. I have it on my KLR650, and it really helps to get the water temp up much more quickly, holds it at a higher temp when it's cool/cold out, and never has any trouble keeping the temp low enough on the hottest of days on the slowest of hard climbs. The KLX doesn't have the temp gauge, but, judging by the fan only coming on RARELY, I surmised that it is somewhat "overbuilt".

I don't think they'll be making a bigger kit than 351, unless they upgrade the cylinder and water jacket design...the 351 sleeve appears to be encroaching on the coolant passageways already...although, not enough to slow the flow (my GUESS...I haven't done any experiments on it, I'm only going by what I know about fluid dynamics). Therefore, I THINK the 351 is on the edge of feasibility due to the current water jacket design constraints. I'd be happy to be proven incorrect...then I'd get the 351 in spite of the desert and long distances out in the middle of no-where!

 

Why not just buy a bike with more displacement?

 

Blackheart, you think too much. It's not that complicated. The 351 works. If it didn't, we'd all know about it by now.

 

Total cost. I nearly stole this bike, and "it works" in stock form, so, I hope to make it shine by upgrading it.

 

Perhaps, but, it was Bill Blue himself that cautioned me about getting the 351, due to the riding conditions I find myself in. After he found out I have a Thermo-Bob on my bike, he THEN said it might work OK if I used Water Wetter. Don't know if I want to push the envelope THAT much....