i have a stock 2006 KLX 250s. I am thinking of putting a pipe and exhaust.
for the same price I could bet a big bore kit from Bill Blue.

does anybody have the 331/351 kit and kept the stock exhaust and carb?
would love to keep very quiet and not do much other mods and have about 5 h.p. more...........that would make the klx a "dream" bike.

waiting for replies!!

 

You need exhaust modification and proper jetting to truly benefit, but the big bore will be an improvement no doubt. You can get exhaust for $150.

Do what floats your boat, but the point of the larger exhaust is to let gases flow freely, the stock system is restrictive to say the least. Bigger motor doesn't add much improvement while still breathing through a straw.

 

I have the 351 kit, rejet the carb and removed smog only. Every thing else is stock. Big difference. I knew what I was getting into when I bought it as a 250. I was only riding back country roads when I bought it. Then I wanted to do some highway riding and the 250 had a hard time keeping up in traffic with out down shifting a lot. I didn't want to buy a new bike so I took a chance with the 351 based on all of the postives I found here. Now with the 351, I put the bike in 6th gear and just go. I can slow down to 35mph without down shifting, then just turn the throttle and it pulls right back up to 60mph in no time. You could buy a header, pipe, snorkel and all of the other stuff, but for me, it would have been a big waste of money. I could not be happier with the bike.

Adding a bigger motor with no other mods makes a big improvement! Never had the front end come off the ground as a 250 with just turning the throttle. Now with the 351 it picks up the front end with out even trying.

 

FW:

2007 GM above is a rarity is going big bore without chasing the other mods first. My '06 is modded as most have done with pipe and jetting first, then big bore. I now think your best bang for the buck is the big bore first with a re-jet. An exhaust will add more on top, but overall I think you're on the right path.

 

Bills' chart on cylinder mod alone is 24.6 hp. Researching the forum seems to indicate that exhaust, airbox, and carb mods gets you into the upper 20's. Kicking in porting/larger intake valves gets you into the 30's. Regardless, apparently, you'll have to add in the cost of stiffer clutch springs with the 351BB either sooner or later.
A DG pipe, DynoJet kit, airbox lid off, and cam mod is about $200 and got me about 20hp (about a 20% increase) and a 27% increase in torque over the stock chart from Kustom Kraft - making me very happy with the performance of the bike. Look up my thread on this. Those were my dyno results but more than a few in here say these mods make more than 20hp. Oh, btw, your 06 will not need the cam mod according to information on the MCM thread.

 

I would never hesitate to put a big bore in a stock engine.

We did a big bore on a stock KLX650 using a Vulcan piston. I had the counterpart in my 650, but I had a pipe, Dial-A-Jet (fuel adder in place of jetting - it works), and some air box lid cutting. The stock pulled really strong, in fact it would slightly jump my bike at the start of a roll on at about 3000 rpm, but then the modified bike started to drive on past. Both would stomp the stock 650 - all for a 25cc gain and not sure about compression, but I think it was actually the same or lower. Might be a better burn pattern due to the piston crown design.

In addition I saw a big bore put on a stock CB900 Honda, no other changes. Way stronger.

If it wasn't a hassle to tear down a top end the first mod I would do is a big bore. The peripheral bolt-ons are just easier to do. I may consider the big bore in short order though.

 

I've got a 292cc kit (OEM Kawa cylinder) on mine with a stock exhaust. It runs fine, gave good boost in accelleration. I recently bought a pipe and have not had the chance to test it with a pipe as well as its winter here.

Pretty sure the big bore kit is the best bang for buck that you can add. It will give way more power than a pipe will give you. That being said, I would still add a pipe to make sure you get the most out of your big bore kit.

If you get a pipe and you are worried about the sound, get the FMF Q4, its the most quiet of all. Adding a powerbomb makes it more quiet (But is expensive) and you can also install a quiet insert with some modifications to make it even more quiet.

 

Thanks for the replies!

Rockabill.....i wish i could get a pipe for $150.00! never have seen that.

2007GM and Idridr:

thanks, you have confirmed what i was thinking, why go get pipe and other things, when a big bore is about the same price and not much more to do.

think i will give bill blue a call

 

Not sure I agree with the "not much more to do" assessment, but the BB kit coupled with proper jetting on the carb should garner a decent power increase. I say that because you're probably going to have to rejet whether you do a pipe plus BB or just the BB, so no work effort saved there. To do the BB install, you'll have to remove and reinstall the stock pipe, so no work effort saved their either. Your reasoning for keeping the bike as quiet as possible and to save money are actually your best elements for going the route you appear to be going. However, I'd suggest one additional upgrade as you do the BB kit...add a Dynojet kit. I don't care what those claim about the ability to use the stock needle. The OEM needle may be one of the weakest links in the whole performance scheme of the OEM bike and carb. Yes, the OEM needle works, but that's like saying the OEM bore works too. When you're struggling to get up a loose, scrabbly trail while riding off road, you'll appreciate every advantage that you can get. The DJ kit needle allows you to have better throttle response that comes on smoothly but with much impoved authority. The OEM needle has a priority to meet emission standards...not to provide good throttle response. The DJ kit might even be worth doing before you decide you need/want the BB kit.

 

I have a used, loud, freshly re-packed, slightly dinged and scratched, loud HMF pipe I'll sell you for $100. Let's make a deal!