Why should they? It would be less costly to dual sport a KX250F!

Really with all honesty, if I wanted that kind of power I'd sell the KLX and buy a KTM350 or the like. I realize what it would take and realize it is not worth trying to do that with this engine.

Some hot rodding makes sense, but going to the extreme is like trying to get a 650 Kaw Ninja to run like a 636 Ninja. They may be near the same size, but to get the 650 to run like the mechanically superior 636 will cost far more than it is worth and make the engine far harder to ride.

Even the Yamaha 250 has higher performance design, using titanium valves and requires more revs and harder riding to perform. Performance will come at a cost, it is a case of is it worth it.

Then there is the whole flow thing... go find the writings of MotoMan and read about what he's learned about keeping intake velocity higher versus sheer flow rate. If it was just getting high flow, the problem would be simple - huge round openings as straight as possible. But if you understand fluid flow you would realize the larger it is for the volume required the slower the flow, but part of the efficiency of a modern four stroke is the ram effect of high velocity flow into the cylinder.

Here is one Car Craft article that hits on the big port theory, proving big flow isn't necessarily the best thing. Here is the one article where I saw the term "Sewer port", it was in Hot Rod. Demonstrated flow isn't everything, velocity is all important.

Unfortunately motorcycle publications no longer do any true high performance build stuff so we get none of this information. I've subscribed to a number of street rod and hot rod magazines and the four stroke performance information to be had is incredible and vast compared to the best offered by current motorcycle publications. I am relearning stuff I remember from the 1970s, which still ring true in today's works.

Check them out and learn a lot.

 

Do you guys even know what a roller cam is?

 

Yeah, it might put out as much as a stock KX250F!

But be harder to ride...

 

yes, it doesn't use tappets like a tappet cam hydraulic roller, flat tappet, mechanical or solid tappet, hydraulic tappet (my favorite),

 

Ahem, very few moto's use tappets. Most certainly Kawa doesn't, get into this century please.

 

No on car engines hahaha!!!! And they still use solid tappets in drag applications for a reason....

I know we use buckets and shims...Which you could theoretically say that the bucket acts like a tappet *edit: "LIFTER"*...

 

My car has no tappets, it is designed like the Kawa.

A lifter is not a tappet. Tappet is slang for 'rocker arm'. If fuelies couldn't use nitro or superchargers, they would not have tappets either. Just say'in.

 

I bet to differ...a lifter is a tappet. A roller cam is designed to be used with roller lifters.



With a flat tappet cam you have flat lifters that touch the cam and inside that you have the push rod that comes up and sits inside the rocket arm. A roller is similiar however the lifters are rollers, not flat.

We could simply be discussing two different engine designs here. I suppose it's hard without specifying. I've only had experience with v8 motors. I can assure you a tappet is not a rocker arm, unless the tappet is eliminated and the rocker is doing the job directly off the cam instead of via pushrod.




To be fair here's a pic of an overhead cam engine, you are correct in this that there is not tappet or lifter, because the rocker arm is acting as the roller tappet against the cam.



Here's a link on tappets and flat tappet vs roller tappet.

https://www.lunatipower.com/Tech/Cam...tOrRoller.aspx

 

My car still don't have any tappets!
Why do they call it adjusting your tappets? There is nothing on the part you are describing to adj. The adj is on the rocker arm like in the bottom diagram. Another dumb word if you ask me.
Why don't they call it a roller tappet, why, cause it sounds questionable!

 

They do call them roller tappets..? Didn't you see the lunati link? You adjust your rocker arms because the pushrod is what is pushing down on the tappet. If you have a loose rocker arm then the tappet is going to float on the cam and that's when you get that tap tap tap tap noise you get with out of spec rocker arms.

Just because shade tree mechanics throw slang terms around for stuff doesn't make it right. They call it adjusting your tappets because by adjusting your rocker arms you are adjusting the clearance between the camshaft and the lifter AKA the tappet.

You don't need to get cranky