Didn't know if there was a classifieds section but wanted to see if anyone had a big bore kit they wanted to get rid of for an 07. Since I will be rebuilding anyway, I figured i might as well ask. Although a new set up would be nice but a little out of the priec range at the moment.

Also, has anyone done a big bore without changing the carb? Is it still effective or pointless. Thanks.

 

The OEM CV carb works fine as long as you jet it properly. You'll get a very noticeable increase with a big bore kit. The displacement almost always benefits an engine's performance, and especially in the KLX's case. My suggestion would be to install a big bore kit and jet the OEM carb accordingly using the many examples that are already present on this forum. Don't open up another can of worms while you're addressing the installation of a different cylinder and such. Keep it simple. After you get the bike running and get everything sorted out, ride it for a bit and see how you like the power. You can always install an aftermarket carb later if you so desire. The OEM carb works. Keep it on there until you get the new kit up and running, and then decide.

 

I've heard the stock carb is useable with up to 331 if jetted properly. It works great with the 300cc jug.

 

He (BB) has a dyno chart on his page showing the 351 kit with the stock carb on.



Mikuni carb results

 

those results are a little low. I had my bike dyno'd on a dynojet and it put up 25hp and 16ftlb's. and i have a slip-on jet kit and open airbox. i would think a 351 with proper jetting would be in the low 30's. Ill let you guys know here in a couple of months. good luck finding a kit guy.

 

Kobra and work, I have heard this from many experts and engine builders. Different dynos can produce some notable differences in power readings, and they warn about making exact power-to-power comparisons from different dynos. I don't know how much stake to put in this, but I read and hear it all the time. They always seem to say that you have to use the same dyno facilities to track finite changes that modifications bring to the engine. Take that for what it's worth.

Kobra, I believe those charts are the one's used by Bake and Bill from the huge thread over on ADV when they were developing the kit. The carbed chart was Bake's bike and the pumper was Bill's. They were not exact in their other modifications for each bike, so you might not be tracking exact influence from the 2 different carbs. I'm not trying to trash their results, but perhaps an exact comparison of the pumper carb's influence isn't 4 horsepower. If I'm wrong here, please clarify.

 

Yeah I see what your saying now. It would be nice to see some updated 351 dyno results with all the free and aftermarket mods done.

 

To REALLY know, it would have to be the same bike, at the same temp and barometric pressure, with the same tire temp, same operator on the same Dyno, freshly calibrated prior to each run, etc. The data can be obtained, but, at what cost? What are the benefits to the person that paid the money? From a business perspective, unless that person were to be selling a product, there is little to no value to doing this...well, if they were racing...but, why would anyone be racing a KLX250s?

 

The benefit is what the dyno exists for. Tuning. It's a tuning tool, used to set up a particular bike/car, etc. Comparisons of different bikes, on different dyno machines is a complete waste of time.

 

Exactly!