Hi I'm new here. I just purchased a 2012 KLX250s and want to know more from the guys who have done the Bill Blue 351 big bore kit. I'm a little more used to riding the motorcross bikes (I have a RMZ450 & YZ250F) and would like for this KLX to have a little more power. I absolutely love riding this bike, its very smooth and very easy to handle. So far the only thing I have done right off the bat was remove the snorkel which gave it a little more breath-ability and a better sound.

Anyways, I would like to know things like:
1. Does the 351 kit decrease the reliability?
2. Does the 351 kit increase vibration (throughout the bike) at idle and higher RPM's?)
3. What other mods need to be done with this big bore kit? (Carb, exhaust, etc.)

Any help is greatly appreciated! Thanks!

 

Anyways, I would like to know things like:
1. Does the 351 kit decrease the reliability?
slightly debatable. There have been very few problems, but it seems that any power increasing modification could result in reliability issues. If there's no power, it shouldn't break. Lots of power, more break. But all in all most of us with 351 kits have been very satisfied.

2. Does the 351 kit increase vibration (throughout the bike) at idle and higher RPM's?)
I didn't notice anything significant. Others reported a minor increase in vibration.

3. What other mods need to be done with this big bore kit? (Carb, exhaust, etc.)
You'll want a better flowing exhaust. The FMF Q4 is popular. Some go with a KDX snorkel. Others say the stock snorkel provides better performance. I pulled my lid altogether, but that's cause my jetting is still a little on the rich side and putting the lid on, without snorkel or with a KDX one, makes it worse. Add a jet kit to the list. Lots of us are happy with the DynoJet kit (I'll suggest the #2206, listed for KLX300, if you're doing the 351 kit).


Welcome to the forum!

 

Hey thanks for the quick response.

Is changing out the cylinder and piston difficult to do or do you recommend having that done by a professional bike shop? I ask because bikes like these aren't very popular around my neck of the woods nor or is a reputable shop..

 

IDRIDR wrote a nice write-up on his install. You might want to check it out and see if it is within your means.

https://www.kawasakiforums.com/forum...351-0-a-36944/

 

I thought it was a very bad idea to run the bike with the lid off without rejetting as it made the bike way to lean? maybe I'm out to lunch so set me straight .
Thanks,
Hunterman.

 

You're correct.
If you open up the air box and/or exhaust, you'll likely need to re-jet. Although some here have said they've added aftermarket silencer (no air box mod) without the need to re-jet.

 

IDRIDR,

Nice photo documentary on the 351 install, it looks very detailed and helpful. I passed the link along to a good bike mechanic here in town so he can look determine what kind of job this will be. Anyway, do you think running mine right now with no lid is a bad idea?

 

I'd never been into a motor before doing the 351 kit. My mechanic skills are admittedly mediocre but I have patience and better mechanics to turn to for questions and help. If you're generally successful with turning wrenches, get a shop manual for the KLX and torque wrenches, and you can probably do it on your own. Have patience and ask questions.

I really don't know. Tribal knowledge says it may be a bad idea to run without lid w/o re-jetting.

 

Yeah I think I'm decent on a wrench, I've been around and helped work enough heavy equipment and machinery over the years that our company mechanic sometimes asks me for my opinion when diagnosing or repairing breakdowns. My only issue is the patience, with this bike I just want it done! When I get to the house I'm going to pull the plug and see what it looks like. I hoping that I'm alright since the factory probably has the carb set on the rich side plus all of this South Louisiana humitidy..

 

So I am a little late in posting this but I wanted to post the 351 kit install with the new carburetor, FMF Powerbomb and Q4. I also changed the rear sprocket to a 39 tooth. I couldn't be more happy with the results and wanted to post a few pics from the install and my ride in West Texas this past November. Hope you will enjoy.