NUMBER 1. WASH YOU BIKE!!!! never open an motor with a dirty bike. I know it may sound dumb but I have seen may pictures of bike apart and the frame is dirty.
2. I agree big time with taking pictures of the cams before you take the out. (that saved my butt)
3. The new piston will have a front and a back. check it twice!

I have about 700 miles on a BB 331 kit - It was one of the best improvements to power I made. I which the 350 kit was around last year- more cubes= more fun.

 

hahahaa.. I hear you on washing the bike.. I had a 99 YZ125 that I didn't wash before doing a clutch job... Added an extra hour onto the job wiping out dirt chunks from the case.. Good times!!!

I will never take apart a dirty bike again

This is going to be fun. I hope. haha

 

Look at that torque curve. What curve? she hits hard right from the start, guys.
Stock carb and stock pipe. The free mods. And that's all.

This is a tractor motor. She hits early and signs off early.




For street work, I use about 6500 rpm as my shift point, sometimes 7000. On the trails, I rarely get above 5000. When you're popping along at low speed in the low gears, and need that quick power, the 351 delivers.

Here's the other dyno run, with Bill's bike. The more drastic variances in the curves are because it had a knobbie tire on the back. I use the Kenda 50/50 DS in 4.50 x 18, and the curve on my run is smoother .



His carb definitely adds some power to the 351 kit. I'm real happy the way mine performs, also.
I have a little bit of tinkering yet to do, a couple of more jetting set-ups I haven't tried. I keep switching one thing at a time, record them in my little book, and move on to the next setting. It's running good right now, but it is just a touch rich across the rev range is what the "sniffer" at the dyno told us.

Because as you can see, the engines both sign off at about 7000 rpm, our feeling is with the big engine pushing so much more air, the head is now at it's limits.

 

So how much did the fun-factor improve?

 

The finished version will have red and orange flames on top of the black.

 

It's like you sold your 250 and bought a KLX351.

 

hahaha, nice.. And I *love* the graphic - let me know when they're available!!

For the mean time I was thinking something like this:



hahaa

 

Would a modified CDI make any difference as to where the engines stop producing or "sign off?"

 

Thats what I did until putting the cylinder back on, then I found it better to zip tie the chain to the guide

can't find the photo but I'm sure you get the idea

 

I'd say the biggest factor separating your power from Bill's is not the carb, but the His supertrap exhaust and higher flow snorkel. The CVK is very capable of producing those figures if you give it enough air flow. In fact, I know of a 315cc CVK34 equipped KLX here in Japan that is producing almost 32hp...although that is with aftermarket cams, and anything but stock exhaust. My point is that your CVK is not the limiting factor.

As far as the drop-off at 7000 goes, the head is just part of what's limiting that. The crankshaft has too much windage, the CDI curve is optimzed for emissions and drivability, the valves and retainers are too heavy and the stock cams are a compromise between street and trail.

I have seen where going with a earlier model CDI, 315cc large bore kit (optimal size for stock head if you're think purley HP), aftermarket cams, and removal of 1.6mm of material from the outside of the flywheel will produce a fairly linear acceleration from zero to about 9,000 rpm. If you want anything beyond that, you are talking about pretty exotic work like re-shaping the combustion chamber and ports, getting lighter valves and retainers (Ti), playing with the valve seat pressure (reducing it), knife-edging the crankshaft (gawd I said 'camshaft' earier. I feel like such a tool!), which includes a lot of balancing work.

One of our board members has been through the entire gamut, and I don't even want to think about how much $$ that required.

Anyway, to turn this bike into high reving beast requires almost a complete transformation of the engine internals. It would be fun if you had the money to throw away and the time to burn, but the ol 'Buy a Husky or KTM' suggestion starts to gain a lot of momentum when you come to that bridge.